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first of the hydrocarbon giisee, and subsequently of the chlorine fraa, are even more disa£n4;able to the tuialyttt than the nitrous fumes evolved during the nitrohydrochloric acid process. 3rd. it is not co rapid as the nltrohydrochlorio aci4 process. 4th. The results do not exhibit a greater accuracy than is obtainable by solution «f the Iron in uttrohydrochloric acid

Mr. Ilmnilton, in h!s article, says: "I have analysed several specimens of pie-iron according' to the solution ia the nkrochlorlc acid method, with all due precautions, which, although exceedingly important, are often omitted in explanations of the process." As M r. Hamilton has also omitted to mention the precautions necessary to observe in carrying out the nitrohydrochloric acid process, I will describe in detail the manner fn whieh I estimate sulphur In Iron and steel by that method, having always found the results trustworthy and accurate.

A weighed quantity (about 3 grammes) of iron is placed in a beaker of about 8001nihilfl— Umiiiii* capacity, and hiving a clock-glass cover. 20 cubic centimetres of strong hydrochloric acid are mixed with 1<> ruble centimetres of strong nitric acid In a small ■ '.-'il;ir. and gently heated until theacid liquid assume* a slightly yellowish tint. The acid is then poured, little at a time, into the beaker containing the iron, the ^lass cover being moved just sufficient to allow of the acid being poured into the beaker. A very strong reaction takes place, aud great heat is generated; but the capacity of the beaker, and the lar^e cooling surface presented by it prevents any loss by effervescence. The solution of the iron is thus effected in two or three minutes, and the whole of the sulphuris oxidised to sulphuric acid. The sides of the beaker and the clock-glass cover are now rinsed by means of the wash-bottle, and the liquid is evaporated nearly to dryness over the water-bath, or on the steam-chest, to remove excess of acid. A few drops of hydrochloric acid are poured on to the residue when nearly dry, and water is added, a gentle heat being applied to hasten the solution. The liquid is then filtered in the ordinary way, the filter paper washed with cold water, and the nitrate diluted to about 100 or 1M cubic centimetres. A solution of chloride of barium is added In excess to the filtrate, which is allowed to stand in a warm place for several hours. The precipitate soon makes its appearance, and settles down at the bottom of the beaker, leaving the liquid above it quite clear. The liquid is now filtered, ana) the precipitated sulphate of barium collected on the filter paper; but it Is important to note that the filter paper must not be washed with hot water until the whole of the yellow solution of Iron has been removed from it by washing with cold water. I mention this particularly, as Mr. Hamilton in hi-; paper says:—M Alter filtering and washing it well with boilioe water, it Is seldom. If ever, possible to render It white, which is objectionable to a careful chemist." This statement and the context would lead one to infer that washing with bailing water is necessary to render the precipitate white, whereas the reverse is the case. After the liquid has passed through the filter paper, the latter should be washed with cold water, amljf a trace of yellow colour remains In any part of the paper, a lew drops of hydrochloric acid added, aod further washing with cold water, will entirely.remove it; the washing may then be continued with hot water. With proper core, and the observance of those precautions, the precipitate, when dried, ignited, and weighed, will be obtained perfectly white. On the other baud, if the paper be washed at first with boiling water, it will a-sumea brown coloration, owing to the precipitation of oxide of Iron, the complete removal of which from the paper is very difficult.

In estimating the sulphur in steel and wrought iron. It is advisable to use a larger quantity, say 0 grammes of the metal and 5) cubic centimetres of the mixed acids. The weighings must be mode on a balance capable of weighing accurately to the tenth part of a milligramme. I use one of Ladd and Oertllug's balances, furnished witli supports for the scale pans, and having agate plane and knife edges.

The acids sometimes contain a trace of sulphurous acid, wVich during the solution of the iron becomes oxidised to sulphuric acid. Before making any estimation of sulphate In iron, it Is therefore necessary to estimate tho weight of sulphate of barium obtaiued from a given volume of the mixed acids. Thus, If (H> cubic centimetres be the volume experimented on, and four milligrammes of Milphato of barium be obtained. then In a determination of sulphur in iron, using 3 grammes of iron and :\0 cubic centimetres of acid, a deduction of two milligrammes from the sulphate of barium obtained will be necessary on account of the impurity in the acid. The following are some of the results which I have obtained by solution in nttrohydrochlonc acid. In my opfniou they are sufficient evidence of the accuracy of the method, and the difference betweeu tho results of the first and second analyses is in each case less than the differences ubtalned by Mr. Hamilton in his experi tnents :—

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THE SOrER RIFLE.

Sin,—Some readers may recollect a description of a riHe invented by Mr. Soper, in Vol. VII., p. 330. Certainly our inventor must be credited with no small amount of Ingenuity and perseverance in being able to produce to the world another and a far superior arm than tho previous one. The former was rejected by the Small-Arms Committee for its /teeming—I say iMtalug Intentionally — complication The one I am about t> describe is simplicity itself. By a very uufortunate decision, however, of the Government, the gun of which 1 give diagram*, has not been considered in the competition, as It could no* by any ftossib'e means be gut ready by the *'.ay stated as the ajt when new inventions would be received. Therefore, for the moment, it has the cold shoulder, but if rival Inventors, experienced mechanicians, the most eminent engineers of England, France, Germany, and tho United States, vivo, as they have given, their opinion that this rew gun is the best in the world, how long will it be before Governments compelled to admit it in competition with others? The requirements of a breech-loader are simplicity, strength, and certainty of action, We will consider for a moment how far the gun we are discussing answers to these requirements. Its constituent parts arc reduced to a minimum, and therefore, of necessity we get simplicity. "The cockiug of the piece, the opening of the breech, and the extracting of the empty cartridge shells are simultaneously effected by one movement of tho hand without changing the nositton of the p lee a. Tho breach is closed bv a block which is hingi d ot pivotted at one* silo of the rear of the barrel, and which Is raised aud tunic4 laterally on its pivot to opeu the breech" (specification^. Fig 1, A, tho breechblock is perforated to allow the insertion of the striker,

her. and still when tried, of course before being cleaned, its action was perfect.

The whole mechanism will however be understood much better by reference to the following diagrams. I have given references to the peculiar parts only; the others, as the barrel, cock, &c.. are similar to tho ordinary rifle.

Fig. 1 represents a side view; Fig. 2 a longitudinal section ; Ftgs. 3 and 4 are end views, with the breechblock raised and closed respectively ; Fig. o shows ihe breechblock.

It may be necessary to say a few words regardiu the extractor, K, Fig. 2. "By the diagram it will h" seen the cud of the extractor is raised, and it is thin part which catches the rim of the cartridge. The ex tractor U moved by means of a lever, and by a peculiar formation of the hammer it is started back with a slow motlon,which is gradually accelerated, and finished with a jerk. By this peculiar motion great force mav be exerted upon the cartridge shell In starting it from the barrel, which Is necessary when the explosion of the cartrldfre, or some other means, has caused to stick tightly iu tho barrel. One screw secures the whole The stock of the gun is in one, aud, ttierefore very "trong. c. H. W. B

PS.—Just at themomentof writing I hear another trial Is to be made as regards rapidity of firing, which I hope to witness, and if more than flo rounds per minute are fired, the Editor shall be duly iuformed.

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Fig. 1. B, by means of which tho blow ot the hamrn'-r Is transmitted to the cartridge. The movements above-mentioned are caused by the motive power being applied to a lever, Fig. 1. D. mounted on the rlzht side, moving in a circular direction, but only to the extent ot 55°. The case of the operation will explain the marvellous rapidity with which this gun has been tired. At the late Basingstoke Exhibition no less than CO rounds were lired by Mr. Warwick In tw minute, work which has never yet been equalled. The only springs used In the mechanism are the ordinary

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INGREDIENTS FOR GOUD FAINT. Sin,—In answer to " Surveyor," (qy. 2500t, I may tell hldi the Ingredients necessary to form airood paint anas follows:— 1st. A genuine well g-nnnd material or paint ocoi«r for the body.

iud. slcealiue or boiled linseed •ii, as a vehicle lor the convenient retention of the paint itself.

3rd. " Patent " orother dryers, to assist the paint in hardening and drying.

Kh. Turpentine or petiolcim. spirit, to give Mtfficiont fluidity to the above mixture, so that it will work readily under the brush. It also nets as a dryer.

The proportions of the above vary, (1) according to the nature of i he paint, (tj according to the kind of surf see to be covered, and [i) according to the weather.

Speaking generally, and taking best ground white lead as an example, lewt. lead, Ogal. boiled oil, 2ilb. patent dryers, and l)gsl turpentine, would makes painl n itable for second coat woik. Fur prim lug or fust coat, say Igal. oil less, lgal. turpentine more; this would cause tlie work to dry " dead *' or flat, as is required. Pale oak varnish is the best lor grained woodwork. If the work is exposed to the weather, ask for ontikte in varn'8u- Unless you buy from a good house you will get varnish made with softer and cheaper gums: this is only tit for inside work.

1 ou cannot well detect adulterated pnints nulessthe adulteration! is uumistaknblv apparent, or you have pure paint by you to serveas'a standard. In this latter case, aBd taking ground white lead again as an example, you may detect adulteration iu this way i Take, say, 50 pnrts lead to 1 part gtoui d Prussian blue or vegetable black, mix together with a given quantity ol'oil and turpentine, and observe the shade Bf blue or grey. Proceed la the same manner with the sample to be tested. I £ this latter lest gives you a darker blue or grey than the former, you may be sure that the latter is the most adulterated. By repnttiif the tests aud diminishing the quantities of lead in the lirst sample, you may make both shades coincide. Note then the difference in the uuniLer of parts of lead to the one part of blue or black, and that will be your estimate as to the superiority of ouo sample over the other. This metliod may be adopted with most colours. Th ■ writer makes au oxide ol iron paint that will stan i this lest favourably against any other he moots with. It is the method he adopts with every sample thai comes wilhiu his reach, and by It he can test each maker's assertions with tolerable accuracy.

As to the last clause of the inquiry, I should think petroleum or other oils would certainly spoil any paint. Petroleum spirit, or mineral turpentine, as It is sometimes called, will answer very well for common outdoor purposes, but at the present price of good turpentine there is very little saving in the u.-e of petroleum spirit. Consumers usually buy paiut In the ground or stiff stale, and thin it themselves. If bought ready for use (a mode the writer would rot generally recommend), the smell ol it would determine whether petroleum spirit, or spirits of turpentine, had been used. If " Surveyor" will insert his address In the advertise ment columns, I shall he happy to forward bim further details. Being iu the trade I do not wish further to speak of this subject, as it would make an advertisement of thfs reply.

Llah

EnttABD Richards, Analytical Chemist to the Barrow Uiematite Iron and Steel Co., Barrow-in-Furness.

mainspring taken from an Enfield rifle, and a flat trigger Bpring. Regarding strength, which is properly of the utmost importance, the gun has many times been fired with a charge of 200 grains of powder and 530 grains of lead. I Lastly, respecting certainty of action, so simple and so certain is it that misfires are unknown iu the vocabulary of its inventor. The ordinary sand clogging has been tried without effect, the base of the cartridge has been sawn asunder, but still no failure, it has bceu left for a fortnight muter water, and during the next two weeks left out in the open air, recollect this was doae during foggy Novem

T11E ORGAN.-SOUNDBOARD, OR BELLOWS

Sm,—Having made the acquaintance of the English Mkchanic some three months ago, being introduced to him by a friend who referred me to one of his articles in elucidation of some mechanical contrivances iu which we were mutually lnteiested, I need scarcely say that I have derived much pleasure in availlug parseif of a copy of his weekly visits ever since. 1 have felt much gratified in the perusal of his pages generally, and more particularly ol late by an stltfcM OB or£*n pipe construction, by/' An Adept," whoce very simple, clear, and minute instructions jjave me encouragement to proceed at once in the construction of m instrument which, for a long- period, I have been rery anxious to commence, I have followed his instrucuoiti in m-iking several experimental pipes (and rery «atUfactorily, as open ones), but, unfortunately, like another of your inquirers, am totally at a loss how to construct stopped pipes; and. taking a hint from •■ Adept's" reply to "Inquirer." cm pas;cG09. No.258. I had. made up my mind to shelve the pipo operations for the present, and proceed with soundboard, or bellows. But here again I timl myself in a fix; for, not tuowini: the scale or relative sizes of the pipes, Iconuot set out my soundboard: and again, as I wish the bellows (,« be just as large as my soundboard and windcheM will conveniently admit, I am consequently brought to a stand. I am desirous that the instrument should comprise—1, stopped diapason, CC to F in alt. or irfmedlara scale), wood; 2, principal; 3, fifteenth; and 4, trumpet metal. And to this end 1 should esteem us a particular favour, answers to the following «4aerie* :— 1. In what number of the English Mecdamc can I find "Adept's" wind-chest and soundboard instructions? 2. Would soundboard 4ft. Gin. by 2ft be sufficiently large (placing the largest 'Octave of pipes in front and at sides) ? 3. What should be the sizes of blocks and thickness of stuff Tor the diapason CC to F or G 7 Simplex.

WOOD PIPES VERSUS ORGAN METAL PIPES

Dear "Itaumonious B.,"—Glad to find the "gout" has not suppressed your defiant crow. 1 always hoped wood pipes would conic to the fore. *' Adept" inun be convinced by this time that metal is not a sine qua rton foranorgau. IIU communications, as original experiments, are of the highest value, nnd I hope he will arrive at speedv convalescence, and be allowed to complete them. There must be men capable of doing this work, and some don't care much for the trammels of the "practical organ builders." I even think the tones of the American org.-in may be rivalled in tkltciotu wood, and 1 like to hear the tone and smell the fragrance of the'goodly cedar. We can jndgeof good tone without the aid of the organ builders, jost as we may pronounce upou a vintage of the "real thing" without the intervention of the licensed victualler. After all " Adept " has done and said, the difficulty ought to vanish.

Henry Usmier, B.A., M.B., Surgeon.

EXTRACTS FROM CORRESPONDENCE.

AMATEUE FARMING. — "A Country Vet" writes -.—" Seeing ft paragraph in your valuable journal ■whether it would cot be advisable to give a column to quotations aud answer, respecting the breediug, keeping, and rearing of horses, Ac. I think myself it would l>e a good idea; but would it not be advisable to add to the abovemeutioned list that! of dogs and poultry, especially as dog aud poultry shows are becoming- so extremely fashionable; and a few hints occasionally on the different diseases in the said animals would not be amiss. I shall be ouly too happy at any time in my humble position to render anything towards its advancement."

BLUE MAHOE WOOD—"Joe "says:-" I enclose you a splint of the so-much-pralscd wood for our humorous friend, 'The U. Blacksmith.' It looks to me very like mahogany in textnre. The price 1 wis asked for a rod of It was about 75 per cent, over what I can procure first-class flehiog-rode for In hickory, lance, or greeuheart. Will the 'H. B." kindly favour me with length and weight of his rods without reel or bag? I might be of service to him if he t» in the market for fly reds. I have given up bait fishing."

ELECTRICAL PSYCHOLOGY.-" B. Q." writes:"T. D. Workiugton says that a positive person can control the will of one who is nogative. Now, Sir, I once proposed to a young lady, and was very positive, and found ber equally negative; and, notwithstanding-, utterly lailed to control her will1 'T. D.' also cays that l>r. Dods 'showed the sighing lover how to choose a congenial partner for life.' The 'sig-hlna lover,-1 suppose, was like the Irishman of the Irish talcs, who first fell in love, and then began to consider who he should be in love with.' On re-reading'T. D.V letter, I find I Lave made a slight mistake. He says that the positive person either ' paralyses ' or ' causes motion ' in the negative individual. I did both in my own affectiug case. The young lady was first

paralysed wilh astonishment, and then vanished

with truly electrical rapidity!"

THE SPHERICAL FORM OF THEEARTn.—2. M. T. Tydcruau says :—" There is one argument in snpport ot the spherical form of the earth, of an eminently practical character that I have never yet jeeu insisted ou, but have repeatedly put to the teat Irom the ciills and shores. If looking towards the sea on a clear day, a perfectly straight edge be held some distance from the eye, amf then be gently lowered down so as just to graze the horizon (where the tea and sky appear to meetl.it will be readily perceived that the woterline Is not straight, but convex, and that the rulo aud the sea, if the former is held perfectly level and steady, first touch j n the centre of the straight edge. This, I think, is occular demonstration, and is almost as good a proof of the earth a rotundity as 1U shadow on the moon.

USEFUL WORK.—" Bemardln" writes : " To my brother readers who may understand German, I tccommend the following work (printed in Latin type) , i"TM"TM*"1''" Jtrpertarium, hurauagegeben von Ur. Kmil Jtcohnt, Berlin, U. Gaertner, 150 p., in Svo. It tssuesevery 0 months, and contains extracts, recipes, *c, from 105 foreign reviews, on bleaching, building materials, dyeing, oils, varnishes, loxtile fubrics, leather preparing, metallurgy, photography, chemicals, Ac., aud. moreover, a bibliographical index of all that baa been published on these matters in those reviews ; io be obtained, I think, at every German bookaeUer'u In Loudon.

REPLLES TO QUERIES.

[103.-1.]—EQUATION.—

x + jr + »= a + * + e #* + cy + az = or + ay \mj 4- Ac = a!* + b- + e5 this problem bus been duly solved. I beg to add a few observations which might extend its utility: I remark that these equations Boivo the problem -. a circle being inscribed lu a triangle, the Bides of which are 2«, 26, 2r, to find the segments x, y, z. formed on the aides by the circle, the relations between these segments are expresjed by the given equatlous.— Gregory.

[2007.]—TEMPERING DRILLS.—" S. T." Is obliged for the loop hole * J. B." has so conflderately left him to leap through, but is not disposed to take the leap, or make use ot the printer's shoulders, as his way out of the suggested difficulty. Tempering, be it that of a drill, or anything else, is the ort of bringing the metal to a certain condition by the application of heat, and by sudden cooling causing It to retain such characteristics aa are thus developod. The condition of the metal is known by a superficial oxidation producing the colours before named; this may be effected in two ways, by hardening 2nd letting down tho temper, or by softening, and then raising it. Tho both systems are adopted, the preference being given to the latter, especially for new tools, as all the finish of surface can be better obtained in tho soft condition of the metal, which finish is uninterfered with by the process advocated, that of laving it on a lump of Iron heated to a sufficiently strong heat in the forge or other fire. The desired temper may be thus secured with tho greatest facility aud exactitude, aa the clean bright metal shows tho degrees of oxidation from the blue upwards most distinctly, which oxidation can be arrested at will. Cleauliness—i.e., brightness of surface, is a nine qua non. Smoke, scale, or other oblitcrative media, prevent the manipulator sati.sfiiclorily judging of the stages of the process, and failure U frequently the result. The criticism of "J. B." had escaped my notice, or I should have replied in the noxt issue.—S. T.

P222.-i.]-WATER rOWER. — In my reply to "G. P.," 2323, there is an error in the number of cubtefcet. "G. P." stated 200antl not" 2-3 "cubic feet, aud at the former I calculated his available power for a turbine. I am the more desirous to be accurate, because the "astounding machine" (I can cnll It no other! of Mr. J. C. Shewnu (which immediately follows my own reply), upsets all practico of hydrauli: engineering. All 1 can say Is, that If Mr. Shewan can produce a "machine" as given ia his replv, I, as an engineer lu good practice, can make his fortune. His statement that "pressure is no object," I do not understand; but let that pass.— Sen Ex.

[2234.]-COLOURED OBJECT GLASS.—SOLOMON'S TELESCOPE.—Whether this is your printer's error or mine, I certainly did not Intend to write such nonsense; of course it is the cye-ylass I refer to. I may here meution, that to each of the day eye-pieces I have pancratic tubes made, which vastly iucrcases their power, both for earth and sky. By merely pulling out this tube, a change can at ouce be made, from viewing tho sun or moon in their entirety, to an iuspectiou of a highly-maguuied portion of their surf aces.—A M Ateu R.

(227.10—MOTION OF WATER. — I refer to "Q. Q. R.'s " answer, April 15th, who states that U-'i) cubic feet per hour, or nearly 15*5 cubio feet per minute, would pass the orifice; but *■ Mltabile Dictu," "Anthony " (April 22) states that25*7 cubio feet would be discharged! (The latter's calculation by his own figures is wrong also).—Senex.

[2280.J-CHINA GRASS SEED.—The seed of I'rtka mrra, of which China grass is a variety, is quoted 5 francs a loth, in the catalogue of MM. Haage and Schmitz, seedsmen, at Erfurth, Prussia, correspondents, I think, of the great London seedsmen.—BerNardin.

[22S6]—GENEVA CYLINDER.— This Is bought, as shown in Fig. 1. In selectiug, the measurement is taken from the height of the lip or pallet E (I, Fig. 1). If there is a very slight difference It is of no importance, as It will only make the part A a little thicker or thinner. Further on will be shown how to get the height when there are no broken pieces to guide. The diameter Is taken by placing a tooth of the 'scape wheel Inside the cylinder, aud then the cylinder between two of the teeth; when the play the tooth has inside tho cylinder, and the cylinder between the two teeth, ought to be equal, taking care not to put them too far Into each other, or else the measurement will be false, but just inside the roundings of the lips. It is best tried (and a second measurement is usual) in a depthlng tool, increasing the depth till the tooth falls fairly outside aud inside, and fails to turn the cylinderProceeding to turn it in, the broken piece is placed at 2, Fig. 1, so that the end of its pivot is level with the lower edge of the Up K, when the corresponding part of the old piece will show how much to shorten the arbor D. Remember always in shortening the arbors to allow for tbe point to be flattened lu finishing the pivots, and a slight weariu the process of turning in; aud taking as much into account in every measurement, riace the part A (3 Fig. 1) on the point of the shortened arbor, and tbe en 4 of tho pivot will show how much to turn away for the shoulder the balance is to rest on. 4, Fig. 1 shows how to proceed with the lower position. Before rivet ting on the balance, the point marked on its rim ought to be in a position to correspond with the ceutre one of the three marked on the plate, when tho wheel is acting in tbe cylinder;. which can be effected by turning the balance round on thecylinder till it does so. Fig. 2 shows how to proceed in "new work." The balance cock, centre wheel and cock, aud 'scape wheel and cock being screwed on tho plate, invert the cylinder to be turned in; placing the surfaee of the lower plug on the surface G of the balance cock, shorten the arbor till the point comes just, below the'scape wheel. (The cylinder turned In complete is shown merely to facilitate.) Since the bottom of '.lie 'scape wheel occupies exactly

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the middle of the notch lu the cylinder, by placing the shortened point on one of the spokes (allowing for flattening and the thickness of the spoke), it can be seen if the surface G opmes exactly In the middle of the notch. Here the adjustments for tho balance aud hairspring collet may be safely turned away (but after the other arbor is shortened and before Its pivot is turned in), roughly taking the height by placing the point ol the shortened arbor In the middle of the space between the 'scape cock S and the centre wheel E, and seeing where the surface G comos on tho collet. With a callipers P P, the npper an* lower endstones F F being off, take the height from hole to hole; shorten the other arbor and Divot it in. Placing the pivot in Its hole, the lower endstone belngscrewed on again, and the balance cock Bllpped on to keep the cylinder upright, seo if the notch Is too high for the 'scape iwheel; in which cose shorten the pivot wtth piece of oilstone or very smooth file to nearly the proper height. Finish fitting on the balance, letting it down till it occupies exactly the middle of the space between the centre wheel E and tbe 'scape cock S; taking care that it fits pretty t'ghtly in its hole, as this is essential to its turning true when rivetted on. Pross it well down all round on the shoulder beforo trying for the height. Fit on the hairspring-collet D D also pretty tightly, and turn in the top pivet. Screw on the balance cock without the endstone. and If the pivot projects through the hole, shorten It flush with the top. Then try again with the index and endstone screwed on, and if the cyliuder Is bound, just free it. Sec that the balance clears the curb-key or pins and stud for the hairspring. Round up aud polish the ende of the pivots, which will give the proper eudshake, and rivet on tho balance.—Nobody. [23381—SAW TEETH.-IU answer to "R. T. S." I scud him a sketch of my favourite form of circular and deal frame saw teeth, tho segment of C aaw tooth are drawn half slie far SO* C saw. the deal saw teeth are the proper size and depth for A speed saw table of

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l.jOorKO, loth are sharpened with tho flat file, boih top and gullet, with about aa much lead as is shown iu the drawing. If" R. T. S." baa a less speed than 7U0 or 750 he must not carry so much hook on C, saw teeth. The way 1 get so much hook on my saw teeth Is by means of thin grindstones, which I put on the saw spiudle. I grind on the back of the stone, the saw being latd flat on the table, having n small jet of water running on the point of contact. Tho operation requires tact and care, as the stones are easily broken.— IIIll Sawteb.

[2370.]-PEl»PER MOTH.—The following answer will perhaps satisfy *' Pupa." The caterpillar of the l'halana Bitulmria Is of a pale colour, and has at the back two black spots. It feedB and is found on the eluia. birch, rose, and the willow—A. Tolhausen,

[2*26]—PIG IRON.—"Ironworker"will find that pig irou, alter having been stocked for tbe length of lime he mentions, hoe little or no sand ou it, whereas new iron is generally well covered with this substance. 1 scarcely need tell him tbat that the sand (silica) excites a scouring action in the furnace, and that it causes the iron to melt thin; no doubt he has observed, that after putting clay on the bridge, In the jambs, or elsewhere, in the furnace, if it (the clay) ha* got on the bottom, or into the iron in any way, the heat has been harder to work than usual. This >i rises from the presence of too much silica, as in the case of the new iron, and, as in the process subsequent to puddling, it cannot be eliminated; the result is, a bard and brittle finished iron.—Cinder.

[2375.]—LIFTING SACKS. — I think the following arrangement of pulleys will suit "Rustlcus. A power of 12.Mb. applied at P will keep2501b. at Win equilibrio, and if the power be Increased it will lift it.—W. II. Tuoarr, Heading.

[2.174.] — BREWING. — " A Reader of Old Books" elves '■ New Subscriber," Incorrect information respecting works on Brewing. "Levesque on Brewing," is published at 'Jl«„ aud Donovan's work can be had in one vol. for 3s. (id. If New Subscriber is in London, and will call at No. 20, Hop Exchange, Southwark-street, he can see copies of all the works In print on the subject.—W. L.

[2382.]—STARTING VALVE-I think the following form of starting valve will suit "A. W. T." It was designed by myself some time ago. It combine* a reversing apparatus and starting valve in one. When

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the slide A is in the position shown in the engraving, the steam tlows from the steam-pipe, through the hole In the slide, and through the hole B in the block to the cylinder. Now if the slide be brought forward so that the other hole iu It is opposite the hole 0, the engine will be reversed. But if the slide is put in the middle the steam will be sbiit off. D is a plan of the face of slide, next the steam-pipe. I have made two holes in it, so that It shall not have to slide far either way, and consequently take up less room. If "A. W. T." adopts this plan, 1 should like to know if he makes it answer.—W. H. Thorpe, Reading.

[24S0.]-FROM MB. G. BATES.—It would hardly become me, as Messrs. Hopkinson and Cos agent, to answer your Leamside correspondent's questions In the manner suggested by him. The best answer I can give Is, that several of the valves are now in working operation at Leamside, which place I pass through weekly, and if he will be good enough to send me his address I shall be glad to explain the working of the valve personally to him, and also fix him one on approval free of cost, which is our usual way of doing business.—George Bates, Engineer, Eastbourne, Darlington.

[24:».]-PROJECTION.-Procecd as in No. 2376, up to finding the line a N; then on any line take m k and n k, equal to A N and a M, and draw it / perpendicular to m k and equal to a a'; join m I and n (, and set off lo.pl, and a' ,•', equal to 1, the side of the cube. Draw

0 q and p r parallel to ( *, and set off b a = g k and rf o equal to v k; then a projector from c' will mark off a e on the plan, and projectors from c and d on the plan, will mark off d and a" on the elevation. A few parallel lines will then. In the usual manner,complete the plan and elevation of the cube. I have given this solution and that to Ne. 8378, because it contains all the lines of construction necessary, and they are simpler, and I have always found them more readily understood than the more general form given by "Bernardln;" indeed

1 believe these are about the shortest and simplest solutions that can be given to these problems.—T. Brown.

[2442.]—MOUNTING 'LARGE CYLINDER,—Mr. Woodleigh can mount his electrical cylinder in the following manner. The caps should be made of metal, as they are neater and stronger than wood, and they should fitotier the necks of the cylinder, which should be slightly roughened with an old file and a little emery and water. The caps should fit loosely, and the easiest way to make them is out of brass tube, with the axis soldered Into it. The cement which 1 have found to answer best for fixing the caps on to a cylinder is made of a mixture of about lib. of resin, .'ioz. beeswax, and a small quantity of rod ochre.— Henrv Chapman.

[2412]-MOUNTING LARGE CYLINDERS. Cylinders for electrical machlnesare generally mounted on wood axles, never metal ones, and as the bole In the centre is generally truer than the rim round the same, the wooden axis Is inserted in the hole, and secured by an electrical cement, made of 4 parts rosin, 4 parts beeswax, and 1 part red ochre, all melted together and applied hot. Care must be taken thar. the mixture is not so hot as to crack the cylinder, and for this purpose it would be as well to warm the latter before applying the former.—T. 8. Comsbee.

[2446.]—MEAT PRESERVING.-The simplest way of preserving meat in tins for a long voyage, consists iu placing the required commodity In a tin case, soldering on the lid, leaving merely a small orifice unsoldered. When a sufficient number of tins have

been thus prepared (a small quantity of water Is sometimes added), they are placed In a tray or vessel, contalog water which is gradually raised to a temperature of 212v, which converts all, or 1 should say, a portion of the water Into steam, which displaces the air previously contained in the case and In the pores of the meat; when this Is done, the hole is closed witb solder, and the meat will keep for a very lengthened period.— T. S. Conisbee.

[2450.J-FASTENING PIN TO BROOCH.—I find that shellac answers very well. The way that I fasten pine on brooches is to melt the shellac on the brooch with a small rod of irou made red-hot, then heat the pin in the flame of a candle or gas-light, then stick the pin when hot In the melted shellac on the brooch. Care to be taken not to handle it until the shellac sets—J. O.

[2*51] — DIAMETERS-TO "AMATEUR." 'Amateur" is not right in the way In which he set about finding tbe size of the sun. The proper way would be to estimate its site as seen by the naked eye, and then to multiply It by the power be has applied, bay the sun appears as 1ft. in diameter to the naked eye, then with a power of oi) It will appear to be 60ft. in diameter.—Scorpio.

[2465.]-COIL— "Induction" asks, is an Inch spark from a coll containing 2lb. of wire as much as he can expect .' Thisfis not near a proportionate result; he ought to get about double that length, aud as the faults of colls generally lie in the bad insulation of the secondary, I should advise him instead of adding more wire, to make perfect what he has done by winding tbe wire again, and taking greater care with the Insulation. In such a >*oll the wire ought not to be brought nearer the vulcauiie ends than Jin. Also tbe farther he works out from the centre the more Insulating material he must use between each layer of wire. He can overcome the second grievance by using a solution of bichromate of potash as a substitute for his enemy, filling both the porous and earthenware pots with it, thus converting a Grove's into a bichromate battery ; it will not be quite so'energetlc lu action, but at tne same time there will not be the least smell.—A. K. Tucker.

[2165.]—COIL—The length of primary coil—viz.. two layers No. 16, Is rather vague, as given by "Induction," as he dues not give cither the length or the diameter. If the primary wire bears tie proper proportion to the secondary coil, he ought to obtain at least a 2in. spark, or supposing a slight fault to have been made in the insulation of two or three of the layers, ljin. It is a'point often lost sight of in making coils, that their action (as their name denotes) depends on the principle of induction, aud when this is taken into account, it is evident that the ultimato result of the secondary coil must be In exact ratio to the cause, —i.e , the primary coll and core. If the proportions are right, I do not think it would be of the slightest use to >dd more wire, but I should be better able to judge If I bad the length of the primary wire given. I have recently been favoured by M. Faurr, with one of his newly invented batteries, which I hear has been tested In competition with one of Grovcs's. In the former case, the galvanometer needle wasdeflected 311°, and iu the latter 40-1, while the permanency was in favour of the former by somejhours. Its construction is as follows:—In place of a platinum plate, we have a vessel made like an ordinary ginger beer bottle, but instead of earthenware, it is made of some plumbago composition, this is filled with nitric acid, and the mouth is stopped with a carbon plug, Into which is screwed a binding screw of ordinary construction; the bottle Is placed inside a zinc plate, bent to encircle It, and the whole is placed In an ordinary round battery jar. The fluid used in tbe outer cell Is common salt and water. In use,this battery gives oft" little it any fumes, is cheap to work, and may be obtained at Elliott, Brothers, Charing-cross. I do not find the fumes from Groves' battery at all Inconvenient, as it can generally be easily placed outside a window, and the connecting wires covered with gutta percha, carried through a small crack left between It and the sill Into the room to the coll. Tho bichromate battery gives a very powerful current, no fumes, and lasts a very short time. It Is practically useless, at least I have found It so, for lectures, or where it Is required for any lengthened period.—F. S. Comsbee.

[246fl.}-SIIBATHlNG IRON SHIPS WITH COPPER.—I think our friend, "The Harmonious Blacksmith," Is misinformed about the Admiralty having adopted permanently, any plan of sheathing iron ships with wood, and afterwards coppering or zinclug them. Many patents have been takeu out with this view, but, so far, none have come Into use, from the difficulty of making complete adherence, also perfect insulation, aud cost of working. Muutz's Metal Con>

fiany brought before the Society of Civil Engineers, ii June 186t, the following plan—viz., a large number of holes, of small diameter, are drilled iu the plates of the ship's sides, a sheet of india-rubber is then so applied, that it not only covers the holes, but completely fills them up, the sheathing is then applied and fixed with suitable nails, ebonised. The cost of working the above would be a bar to its general adoption. Another patent leaves out bolts at certain distances, to be afterwards lilted up with the bolts fastening the wooden sheathing; here the difficulty, as In many others, Is so to cover the heads of the Iron bolts with some composition as to prevent galvanic action. Zinc sheathing is not a good detergent from fouling, and was introduced some years since to cover tbe bottom of colonial built vessels, iron fastened; were it efficacious in preventing fouling, It would be easy to galvanise the iron ot vessels; but galvanised iron rapidly fouls, and vessels using It require constant clearing. Copper and Muntz metal seem to be the only preventives so far known, and many compositions having copper, &c. for their base, have been tried with varying success; tbe latest, and I believe the most successful is a thick coating of some adhesive material, painted on hot, and copper in miuute particles, dredged on and rolled to make a smooth surface. Arsenious acid has also been tried, but itsoou destroys the plates; so does the red lead paints, and so far the right thiug has yet to be discovered. Several patents have also been advertised to clean the bottoms of vessels by brushes, &c,

while afloat, but the tenacious adherence of barnacles seaweed, and slime, render* all such efforts futHe.— Patience And Perseverance.

[247I.]-SUMMER BEVERAGE—LEMONADE — Pour one pint of boiling water on JHb. loaf Suitsj»oz. citric acid, two pennyworth essence of lenuor/ dissolve the acid ia a little of tbe liquor in a teruup drop the essence of lemon on a piece or two of the loaf sugar, and drop them in the liquor, stir it well when all dissolved, strain through apiece of muslin or a wire strainer Into a decanter; it will keep for a long time ; mix it as you would greg. If a little more water is used it will not matter; lc will not be quite so strong. Tried and approved. Some think a dash ol wine or brandy is an improvement.—Grocer.

[24740-APPOLD PC.UP.-Tbe makers publish the sizesof the pumps, and the particulars of the quantity of water thrown : sizes of pipes required &e but they do not give the number of revolutions the p limp requires to make, whieh I believe they keep to themselves, for what reason I do net know • I hava> adduced the following formula from experience. For instance: class 1, 6' diameter,class2,8'dia. class3 V diameter, and so on:

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The useful effect is said to average about 75 per <mnt Molesworth's formula is very incomplete and requires the divisional number as above to tint he ^liferent sizes or diameters of the pumps.—a^scx.

[2479.] - MUSIC.-" Clerk " having ent,r ed music plates, had better send them to somo l.tho musie printer, who would transfer copy of same on to stone. fills process ia much cheaper than printing from the plate, and far better in appearance.— Zetis.

[2482.J-FUEL FOR PORTABLE ENGINE-I have never found that coke of ordinary quality injured the fire-box of a portable engine more than coal in fact, from the relative cheapness of the two fuels" coke is more economical, even supposing that the fire' box were more rapidly deteriorated by its use. '■ Subscriber" will, however, find his tubes require cleaningout more frequently when using coke, owln^r to tho quantity of fine dust caused by its combustion. With the worst samples of coke (those containing the most sulphur), the wear and tear is very slight indeed, mid the difference between coal and coke would be so e.'uall, as hardly to admit of being described as a percentage. —T. S. Comsbee.

[2485]-GALVANIC ENGINE.-I beg to inform "Old Salt" that the electro magnetic engine which he wishes for information about was Invented by Professor Jacob!, of St. Petersburg. That engine is said to have propelled a boat carrying 12 persons against the stream on the river Neva. The construction was as follows :—There were 8 electro magnets fixed on to 2 discs of wood ; the one disc stationary', and tbe other movable. Tho faces of the poles of the magnets were made to pass almost, but not quite, in contact with each other. The commutators of the engine were so arranged that as the moveable disc revolved, and its magnets were approaching those on the fixed discs, the poles were of the opposite kind, therefore they were attracted towards each other; but as soon as the momentum of the machine had carried it so far that the ceutres of the magnets bad passed each other, the current was changed, so that the poles became of the same kind; and therefore the-v repelled each other, and thus rotation was produced. 1 never saw a detailed account of the above invention, and this account which I send Is mainly taken from Lardner's "Electrlcity{aud Magnetism." My own opinion Is that In such an engine, there would be very little power, as of course you only get the effect of the lateral pull of the magnet. I have had some experience in electro magnetic engines, and the more I know of the matter, the less probability I see of any practicable application of electro motive po^er as a substitute lor steam.—Henry Chapman.

[2497.J-FROM " A THINKER/— In answer to Vor.stant Subscriber," the width ef frame at seat is 20in.. the width between the centres of tiers of grinding wheels, 2ft 7}in.; length of cranks, 7iin. ; distaoce of bar (on which the front levers work) from the seat, 16in. ; height of said bar from the ground, 2fL ; length of levers below fulcrum to centre of working joint, ltsjin.; length above fulcrum, 22in.; length ol connecting rods from centre to centre, 3ft. Oin.; distance between centres of levers, 131a.; distance of axle cf driving wheel from axle of guiding ditto. 2ft. Sin.; height of top of seat board, above axle of guidinir wheels, 9.J in. ; a vertical line from front edge of seat board would be 2{ln. from axle of guiding wheels; the lower board Hiu. less; the box lid slopes and turns downwards; extreme width of seat board, 19in.; extreme breadth of ditto, llftin.; foot treadle from fulcrum of levers, 16I».; length of guiding levers, 2ft.; distance of their connecting rods frTu fulcrum, 71n. The connecting rods run in an horizontal line from the axle, and their working joints are rather large, so as to give some play room when in use; the guiding levers arc enclosed at each end of the lower board, in a light iron rail to support them ; the above dimensions are for an average-sized mac The form and composition of the frame may be judged objectionable, but with the addition of only about 51b. to the weight, I have at once firmness ana steadiness, also durability and lightness in appearance. — A Tbinker.

12409.J-APPARENT ANOMALY. - My inquiries friend is quite correct in stating that the avoirdupois weight coutains 7000 grains troy, but the 24 grains to the dwt. does not belong to avoirdupois, but to troy weight, which contains 5760 grains, the ounce trov being quite different to the ounce avoirdupois.—H. Stephenson.

[2505.J-WEIGHT OF WATER—A cubic foot of rain water, when the barometer stands at 29-5 metres, weighs lOOOoz., or 6251b. Sea water = 64 Ulb.— Senex.

iPBiL 29, 1870.]

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.iiiro-msts that we (your readers) should bring our •■bricks "and I therefore venture to contribute mine. I hive always considered the study of galvanic batteries with a view to economy and constancy to

('riiiMiaiik's. which consists of plates of copper and rinc cemented into a wooden troughami exceed by a weak solution of sulphuric acid and water. This bat tVry althouglii most important Improvementat the Jfm..' it was invented, is now entirely superseded. Smte-sbTtttryis a very usefuParrangement for exnerimental use it ia not wanted to be very constant, Kr to he kept in action for a long time. The con"ruction of it is as follows: There is »«'*«•«» vessel to contain the exciting rotut Ion, which.oonsiss of one part sulphuric acid to about 7 of water. The

„ cgrtiw"plate is made of P»««»,^J»lOTii£llS tie held in a wooden orgutta percha frame between the two Dosltlve plates, which are made of zinc. W?« the most Dowerful battery that I have seen or used Is one^nveJted"bout1852 V Mr. Martyn. J. Roberts, ooth^re'glrdB constancy, intensity anquan £

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iiitl-LONGITCDE.—Difference in time between Belfast and Glasgow, 6 mln. 40 see—D. B.

[2528.J-SUBMARINE LAMP.-No lamp could be «ed"Srlth air by a single tube. Every miner knows thst to obtain a proper supply, a current must be established by means of a "down cast" and "up cast "shaft. This could be effected without much dfficulty inthecase of Mr. W. A. Hackett's lamp which may be taken to represent a mine on a small .cite. But common india-rubber tubing will not do, as it would be throttled by the pressure of the water H must get some tubing kept disturbed by a coll of wire inside, such as the divers use This is enough on the general question; but if Mr. Hnckett has any practical T.bject in view, I shall be happy to supply him with further detalls.-Tuici,ORirs.

[2534.1—SOLUTION WANTED—If "Minnehaha" will draw the figure of his problem, using the same letters as in his query, and join D E, he will And that, since A C = 2 E C, and B C = 2 C D, and the angle A C B Is common to the two triangle. AB C, D C E, A B = 2 E D, and the angles C E D. C D E = C A B, C B A, respectively; therefore D E is parallel to A IS; therefore the angles BEjD, ADE = ABE, B A Drespectively; therefore the triangles similar; and A G : D G :: that A G = 2 D G — Hoao.

[2534,1-SOLUTION WANTED.-Join D with E, then by similar triangles ABGandEDGwe have AG:DG = AB:DE = AC:CE = 2:1

(by construction) therefore

A G = 2 D G.
Ois the centre of gravity of the plane ABC.

A. Tolhausen. [2534.J-SOLUTION WANTED.—The straight lines A D, B E bisecting the sides of B C, A O of a triangle.

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Sro?nega lve SaWs, which are made of pure platinum. I haveusedla oatteryof thutklndlconiinunlly for many consecutive hourB?for the electric light without being aWett) detect the slightest variation in the current The d?sadv°nt»Ses are the cost of construction and working and the large quantity of fumes evolved from he n Hro'usacid1 Tnere are several other kind, of .ingle fluid bSteries but those I have mentioned I think It, ttemos Tmportantof them, and I now pass on to h' doubl'flu id kind. Daniels constant battery consists ofa copper vessel, which at one and the same tm'holds one of the fluids (a.atmated solution of InTnhate of copper), and forms the negative p ate Within the coppe? vessel Is placed the porous celt and in that ii nlnced the positive plate, made of a thick rodof zinc and the other fluid, 1 of sulphuric acid tToof water This battery Is a very convenience KTM?thi. er?n.tnncv of its action and the absence of furnV The M^nooi" battery, invented by FrofrsXcallan is a very powerful, but a very unninnJmt oneto workwlfli.on account of the nitrous f^mes given off from it. I. is arranged as follows :There is ail outer vessel made of est iron, which Erms the negative plate, and hold, the one fluid (undUuted nitrous acid., in other respect, the arrangement «»the^ame a^ the preceding one Grove.'. bsttery 18 one of the most useful, I think the most. It

P ,.L V. Miom An outer eel of earthenware

iidSn6innerpo?o^scel" the negative plttf.i.made of pUtlium and the two positive, are zinc, the fluid, used are "for the negative plate In the. porous cell pure nitric ilid although I think nltro-sulphuric isbetter The fluid for the positive plate is 1 of sulphuric acid to 6 or 7 of water. Bunsen's battery Is similar to Grove.', excepting that the negative plate is made of carbon cut from the graphite deposited in gas retorts Some years since (with a view to economy) I tried aliniinlum instead of platinum for a negative olate but although I got a fair current from it, I did Sot consider it atfnll equal to Groves', an^ one Adog fatal to it wa. that the aluminium was slowly dlssoKed by the nitric acid, and I therefore d.scont nued to use it In all the above arrangements tbezluc Is amalgamated with mcrcury.-H.N8Y Chapman.

[2547.J-PRINTING NAMES ON PLANS.-A very pretty and easy method of printing the names on j

plans, &c, pi by drawing out I M Iff

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[2.141 ]—GALVANIC BATTERIES. — Mr. V. M. Beecliey a»k. for information on the above subject, and

iug. If "Laud Surveyor

will try he will not And much difficulty to conten d

against.—A. Tolhausen.

[25491-SCREW STEAMER—I consider that an engine of one horse power would be ample for such a boat as Mr. Douglass M'Carthy mentions, but a vertical direct acting engine would be better than a horizontal one.—Henry Chapman.

[2555.1—ECHO.—An Ayrshire amateur can produce an echo on the cornet by simply putting a .Ilk handkerchief up the bell, but it is usually dona by putting a mute (to be had at any music warehouse) iuto the bell Some cornets have a special arrangement for producing the above effect.-henry Chapman.

[2557.]-COI'P ER COIN.-A German counter. I believe, I have several varieties of it, all thin and with badly engraved inscriptions. No value.-B£R

NARDIN. ,

T25611-BOOKS.—The following dimensions are, 1 believe correct :-Imperial 8vo 11 by 7j; super, royal 8vo.,10, by 6J;royal 8vo., 10 by 6|; demy 8vo. 8} by 51 i post 8vo!?7, by 21 crown 8vo 71 by 5 ; demy l5mo 74 bv « royal 18mo., «J by 44.; foolscap 8vo., Iflyti?i2p2alsImo.. 54 by 3); deuiy Wmo.,5,by '14-foolactD 12ma, 54 by 3J; royal 32mo., 5 by 3, demy 32moP; i, by'2, ? demy W, 31 by 2tin.; edges uncut.—Busy Bee.

[2S61.1-SIZES OF BOOKS.-It I. almost impossible to give " F. F." the exact size, of book., because paper. a?e not made " true ; " but I will endeavour^o explnln the matter to him. When a book Uewrftol as belnjj crown 8vo, or fcap 8vo, it i; meant that the "sheet " is folded so as to print, on the two sides, 10 pages. In the same way 12mo means that the sheet is bo folded as to contain 12 pages on each side,.«, 24 pages. ISino would therefore be 36 pages to the sheet • 32mo. 64 pnajes. When no description of the naper is given, demv is usually tho size meant; but In this partTcular the wording of advertisements s verv_ aibitrary. The size of the last volume of. pur Mechanic wa. demy 4to, though to suit the exigencies of printing the 32 page. .were printed oaoM sheet equal to four sheets of demy. As F. *. is doubtlesa aware, there are various names given to

different sized sheet, of paper, tho dimension, of which I give, and he has merely to fold a sheet to take in either8, 16, 24. .T2, .16, or 04 pages to get at the measurement of any sized book he is likely to meet in the ordinary course of life. If I had a rule and tho books handy I would t-ive the dimensions he ask« for; but I think I have made it sufficiently plain. A slight reduction should of course be made for "trimming edge., but that again is compensated for by the covers of the book. Size, of sheet, of paper ^Imperial, 30 by 22; super-royal, 28 by 20: royal, 844. by lOj; medium. 33, by 181 demy. 22 by 174; large post •i\ by 16: post. 19 by 15; foolscap, 17 by LMn. With these dimensions given it will be easy to fold up a sheet to any required size of page and the measurement will tlien be plain enough. But If "F. F.' cannot understand, and will let me know, I will " try again. —saul, Rymea.

[2563.1 - SMALL COPPER COIN. - The great scarcity of halfpennies and farthings, coined by government, led to the Issue, about 1648, of the small^ copper and brass pieces failed "tradesmen's tokens. They were struck, as their name indicates, by private tradesmen, for the use of their customers; and also. but more rarely, for the use of a whole village, borough, town, or city. These latter wore usually called*" town pieces," and your correspondent's coin is one of them. It 1. engraved in Soiling's "Copper Coinage," plate 1, No. 32, and Is most Ilk ly ahalf penny stwick by the corporation of Dover.—Henry \V. Herfrey, M.N.S., &c, Ac, Markhnm-house, Brighton. [256.-11-SM ALL COPPER COIN.-Thls copper coin wis probably issued by the;town authorities of Dover, such coins, or tokens as they are more correctly termed, being very numerous at that period. Hie design on the rev. is described by Boyne In his list of the Trth century tokens, p.130, No. 160. " St. Martin on horseback, dividing his cloak with a beggar wto Is following hlin." To which is appended the following note —St. Martin in Roman Catholic times was patron, Sarute of Dover, and the Church of St Martln-leGrand the mother-church. AmongBt its other privilege, was thnt of beginning service before all the other churches and chapel, in the district. The church was destroyed at the time of the Reformation, Dover Fair Is still called St. Martin's Fair. The Bame device is on the token, on the Borough Counter-seal which dates as far back as the year 1305. This has been described by Browne Willis a. "11 highwayman robbing a man on foot."—D. r Batty.

[2564 1—LEADEN COIN.—Uprobably a token of the time of Elizabeth. I possess similar ones reputed to be of that period, but cannot bring any authority to bear. 1 shall be equally obliged wiih "Old Coin for any aufaorifcifMK information upon It. — D. 1. Batty, 9, Fennell-street, Manchester.

[2566 j—TOOTH-POWDER— Camphoratedjchalk is very good, and economical as well. The following is also recommended :-Orris root, 1 ounce; gum myrrh 1 ounce ; nutmeg, finely powdered, 1 scruple ; chalk 1 ounce ; mix. Proved.—Busy Bee.

['560 1-TOOTH POWDER.—Prepared chalk jib, camphor ldr. The camphor must bo finely powdered by moistening it with a little spirits of wine, aud then intimately mixed with the chalk. Kxtrocted.—Minnehaha.

[2577.]-BORING GLASS.-" C. H." oan bore a hole inhis glass sheet, in the following way: Let himmark or scratch a ring, of the size .and In the pli ce lequired on each elde of the sheet. These rings will, ol course exactly correspond. Then let bun mark out a aeries of uoiuts pretty near each other, round the circumlerence of the rings, taking care that these points shall also, in every respect, exactly correspond with each other. He should then fix uprightly in a vice a smooth pointed steel punch, and arming himself with a similar punch and small hammer, get some assistant to hold the fcbiss sheet horizontally with one of the circumferential noints, .teadily resting upon the upright punch. Apnlvin" hi. own punch to the same point on the um.er surface of the glasB, and using gentle blows of tic hammer, he will soon work hi. way down through tie Bheet until the two punche* meet, leaving a small perforation without causing the slightest >»• Oinless he is clumsy). Repeating the process at other points, all round the circle, he will find at last that th.

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ncluded dlso can be readily kuocked out by a slight tap leaving the required hole: where rough edge, cau be amoothed off by a file.—Mechanicub.

FILES SHARPENED BY GALVANIC CURRENT.-A very Interesting and economical Proce»» for re-sharpening tiles has been exhibited before the SoehHe " Encouragement of Paris by M. WerdcrmanB. Well-worn Tiles are first carefully cleaned by means of hot water and soda; thev are then placedIt, connection with the positive pole 0/a battery, ins, bath comoosed of 40 part, of sulphuric acid, SO parts ol nitric-acid,and 1060 parts of water. The negative pole U formed of a copper spiral surrounding the files, >ut not torching them; the coll terminate, in a wire which SAwards the surface. This arrangement is the result of pract oal experience. When the files havotecn ten minute, in the bath toMstaM washed and dried, when the wholeof the hollows will be found to have been attacked in a very sensible manner ; but should the effect not be sufficient, they are replaced for the same perio 1 as before.

RESTORING LIFE.-In consequence of the experiment, of M. Labordette, tho National Lifeboat Institution ha. decided on omittiug from it. new instructions tho statement thatamong the appearances which generally accompany death the 'jaws are clenched and the fingers seml-contrnctcd." Dr. Laborde.tL s cxperimentsVn animals, have clearly proved that In nine of twelve cases, after clenching of the jaws Sr., had been observed, life had been re stored; and has given several instances ot human beings having btou resuscitated under similar circumstances Be has also in the strongest manner expressed his opinion, founded on these facts, that the clenching of the jaws and contraction of the fingers, after short '""ers'on. indicated remaining vitality, and that the same should enconrage perseverance in the efforts to restore inc.

KOTES AID QUERIES.

[2580.] — LARGE TKLK8COPES. —I would ask some correspondent who can give a reply, if lie know* where it la poaaible for a working man like mrwlf, who cannot afford to purchase a large telescope, to obtain the privilege of occasionally looking at some of the wonders of the heavens with a powerful instrument. I have a small, but beautiful defining telescope, of ljin. aperture, which will divide double stars as'close a» 3}'; for instance, it and J Bootis, K Aqnaril> t Pegasl, but when I read the accounts of astronomers, and what they have seen with their gigantic telescopes, T long to see some of the wonders they describe. Some years ago, I believe, Mr. Slater, the optician, nsed to exhibit a large Kqnatorenl at his house In the Euston-road, but It has now disappeared. Two or three street telescopes, of 4ln. or Sin. aperture, I have looked through, but not one of them was of any account?—G. F.

[258l.]-GUTTA PERCHA SHOES.—'Will some of the obliging'correspondents of our journal, favour me with information on the following queries? 1. Are gutta pcrcha shoes injurious for the cyosight, if so. why? 2. Which wav shall I proceed to^ro-sole an old pair of gutta percha' shoe»? If possible, state price of the material (gutta percha), and how sold ?—Li. E. William B.

[2582.J-WEIGHT OF FRUSTRTJM. Ac—A frdstrum of an iron cone has a height *f 12ft., the diameter at the smaller end is 2ft., and at the larger end 4ft. A cubic foot of iron = 4t01b.; what will the weight of the frustrum be, and supposing that 4 tons weight be cut off the lesser end of the frustrum, what will be the diameter at the p.ane of section, and tho height of the frustrum left ?-0. H. S.

[2583.]—THE '• ENGLISH" VELOCIPEDE.—Will "A Thinker" oblige me. with a further description of the steerage of the " English " velocipede, (a description of which occurs in the English Mechanic of April 8th), as I think of making one on his principle, but cannot quite understand how he guides it, whether from the front or hind wheels? Likewise, will some reader Infbjm me if it is beat, previous to drtvlpg In the spokes, to soak the wooden nave of a wheel in hot water, or not?—C. T. W.

[2584.}—SULPHATE OF LEAD BATTERY.—I should feel obliged if "A Good Boy" will send full directions for charging the battery, also if the zinc should be amalgamated, and how much lead should be put into a On. porous pot; by so^dolng, he will much oblige, as I havo the materials ready, according to directions given in Query 218* 1—Carfax.

[2585.]—FLOCK PAPERHANGINGS.—I should be obliged by any one practically acquainted with tho manufacture of paperhanglngs, to inform me how "flock" paper is made; also, if the gold patterns on same are printed on the paper tefore or aftsr the flock is laid on? Information in detail Is sought.—Zbtus. [2586.]—WHEEL MAKING.-Will some brother mechanic give mo information relative to the best kind of machinery for forming carriage or cart wheel spokes, and any other part of wheels?—Inquirer.

[2587.1-CHINA GRASS.—Can any of my fellow subscribers Inform me where I can got a small quantity of China grass ?—C. Katk \.

[25RS1 — EQUATOREAL MOTJNTTNG.-I should feel obliged if ''Hyperion " would answer my querv respecting his mounting, No. 1792, in No. 258, Vol. X. —Neptune, No. 1.

P&m}— RAISING WATER.—With respect to my forsier query, respecting raising water, as "Machinator" did not seem to nnderstand me, I will try to explain myself more fully. I do not want the water rarsed to the dam above, as he seems to think, but to supply a cistern with fresh water. It Is not needful to bf a continuous stream. I want It from a mill tall, so a« not In any way to Interfere with the working of trie water-wneel. It will require to be raised 8 or 10ft. rich, but no particular quantity.—Neptune, No. 1.

[2590.)—BOOKS WANTED.—Can any of my fellow-caders tell mo the names and prices of any works now published, on the construction and details of small engines, fiom 1 to 3 horse power, either vertleal or horizontal ?—E. B.

[2591.1-FLYING MACHINE.-I wish to make n model of a flying machine; could somo kind brother reader give me the following information? How much gas In a bladder would It require to raise 3oz.? What kind of bladder would be tho best to contain the gas, also size of same, and also what kind of gas? Would the common coal gas do ?—Casual Observer.

[2592.]-DEW-CAPS TO TELESCOPES.—Would Jlr. Illacklock or Mr. Pnrkiss, be so kind as to say whethor it Is necessary to nse a dew-cap with a reflecting telescope (api-rturc din.). In order to prevent the condensation of moisture on the plane mirror ; if so, what length should it be, or if there be any other method of protecting the plane ?—Hugo.

[2593.]—DEFECTIVE'BATTERY—For n number of yean I have been unable to labour through HI health. For several months? I have been using one of Smee's electric machines, and feel slightly better. It went well for a time, but of late has been going very feebly, the vibrating often stopping. Occasionally it would go a few minutes or seconds, if the linger were gently pressed on the screw above the vibrator. Recently, when trying to discover what Wrb wrong with it, two of the zinc plates got loose when In the acid, and In trying to tighten the screw, the Bllver plate bent and touched one of the former, producing a hissing BOund,"wkitenlng and thickeniog the acid. I removed It as quickly as possible, and straightened and fastened it properly. Since then I can get no vibratory action, whether from the above caaee or not. I cannot say. The zinc plates were amalgamated immediately before it stopped. I put in Iresh acid (1 to 8 of water), but this brought no Improvement. Perliapa the silver plates require platinising. May I ask it [hey are done with the same material (mercury), and iu the same way, as the zinc plates? I would be truly

obliged to any reader of tho Mechanic, who may have the Knowledge and experience, for any hints which would enable me to get the machine into working' order?—G. F. L.

[2594.] — BORING WOODEN HANDLES IN LATHE.—Will some reader tell m<? how to bore wooden handles in the lathe, after they are turned ready for driving the tool In. There was a query on this subject December 17th, ;but 1 . have seen no answer. .Perhaps "J.-K. P." will oblige by recommending a method of doing it ?—A. B.

[2595.J-PRO.JECTION.-TO "BERNARDIN."— Your able reply on this subject on page 93. induces me to ask If you would Inform me of any work that explains the whole subject thoroughly. I have gone nearly through Davidson's book In CasseU's series, but there is evidently mnch beyond what that book teaches ?—J. H. Yewdall.

[2.m]-BUSY BEE.-Could some »f my fellow subscribers kindly reply to a few queries contained in the last dozen back numbers, bearing the above signature? One answer to 12 or 14 queries !—Bear Bf.e.

[2597.]—BEESWAX.-I shall feel much obliged If some contributor will kindly give a recipe tor maklog beeswax, common, only sold iu th eoll and colour shops, the principal Ingredient of which Is yellow nuin, or could any one name a book, where I could find a recipe for making it?—Homo.

[2598.]—ELECTRIC—Will "Sigma," or somo other electrical correspondent, kindly state If aLeydenJar may be charged by a glass tube, oxelted by being rubbed with flannel, sufficiently to give shocks, Jcc. and if so, what ought to be the length aud diameter of the tube ?—Slasher.

- [2599.1 — HANDRAILING. — Can any brother reader inform me of a cheap work on handralling and staircasing, or whether there is an American work out, and the price of It?—Patelet Iiriuok.

[2000.]-CLEANING OF DIATOMS.—Will any of your readers have the kindness to give a little information how to overcome the following difficulty? I havo tried two or three times to prepare diatoms for the microscope, but with only partial success—not those found in guano and other earths, but the living diatoms. I can succeed, by tho aid of muriatic and nitric acids, in getting the diatoms quite clean, and to show the markings very well; but I cannot get rid of a fine filamentous sort of network, which appears to be some sort of vegetable remains. I have boiled them In nitric acid till the diatoms have been injured or destroyed, but the result has been the same. I should feel truly obliged to any one who will tell me how to vanquish this enemy to a neat and perfect slide. I have read several books on the subject, but can get no information on this particular point. What I now seek for is, some brother reader's practical experience.— Beaten.

fBtj01.]-VENU8.—On the 1st of November, 1871, Veuus will be at her greatest brilliancy; will " Omlcroa," or some other clever astronomer, please to show how the computation is to be made, according to the formula given at page 509, Vol. X., viz. :—

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r* A3 Where

R — radius vector of the earth = -9919. Its log. = 9-9965.

A = log. dist. of Venus from the earth = 9 62.11.

r = radius vector of Venus = 7215, Ita log. 9 8583.

G. Firtu.

[26D2.J—LOSS OF TASTE.—Can any reader Inform me of a preparation, medical or other, for restoring suiell and taste, lost for some months, from a bad cold?-W. P.

[2603.]—BOOK WANTED.-I am In want of a practical work upon the duties of a rail mill manager, with instructions as to the various calculations which enter into that business. If such a •■ ork is in existance, will some fellow subscriber give publisher's name and address, and title of book ?—J. Jonei.

[2604.]—PROBLEM.—I beg to thank Mr. Tolhausen and Mr. Biggs for their replies to my query (2180). In last week's and this week's Mechanic. Would some of your mathematical correspondents kindly give me a few hints as to the solution of the following, which I extract from the Science and Art Department Examination papers a year or two ago? "Two points are 2 and25ln. from the centre of a circle of lln. radius, and 3in. from each other. Draw the circle which, passing through these two points, shall touch tho given circle."—Y. P. W.

[2605.]-TRISECTION OF AN ANGLE.—I have tried the method recommended by " Vibrator," in this week's English Mechanic, and have found it to act as described in the case of the obtuse angle, but iu the ease of the acute angle, does not the polut O (page 8'Jj, fall on the outside of B A? 1 make it so. In that case

1 suppose the distance F P would be added to B D, and the arc described from It with It D + D 2 as radius. Would not the same principle apply to the division of angles Into any number of equal parts, with this difference—viz., Suppose the angle A B C (page 89), to be divided into five equal pirts; on B O mark off five equal distances, proceed us before; mark off the distance H L on the fifth arc, join the fifth point with B, and where this straight line cuts the arc E II (say in the point x), mark off E i from tho fifth point on is C, and proceed as in the other case. Again, suppose the angle A B C la to bo divided into seven equal parts; on B C mark off any seven equal distances, BD,I)E I K. draw the arcs L I), M K, N F, O G, P H,

2 I, and R K, bisect the angle A B (J by the line B X, cutting M E in S, mark off the distance S E on the arc R K from the point K—viz , the points 1, S, 3, 4,5, fl, and 7; join 7 B. cutting the arc N F In the point T, from the pclnt K mark off K V, eqaial to N T, and from B with B V as radius, describe the arc V U, and the distance s E will divide the aro U V into seven equal parte, whence the angle ABC Is divided into seven equal part" as reqnlred. On seeing the article on the "Trisectlon of an Angle," in this number of the MeChanic, it struck me that by a somewhat similar method, an angle might be divided iuto any number of equal parts, and I have thus attempted It in the

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trisecting the angle, L a Is marked oil from Fociiu In dividing the angle into live equal part*, M J w marked off from II on B 11, and In dividing the angle Into seven equal parts, N T is marked off from K on B h, At. Ac, whilst the distance 8 E. marked on tholast arc, rem.niuB the same for all divisions of the angle.—Y. P. W.

[2606.] — DAWN, &c—What countries have furlongest dawn and twilight, and why .'—david K. Williams.

[2«07.]-HEATlNG GREENHOUSES. -W any reader give me some practical instructions for r».:.stlnp a small greenhouse, say 10x4? I have read all tinnotes recently inserted, but they do not contain anything sufficiently detailed. I want particulars of rost of the various methods. The small amount of attco'-ion requisite, economy, and durability, are essentia) de*.idorata. Does any one know anything of ilussest's system? Information will be useful to many besides. Saul Rymea.

[J608.J-SULPHATK OF ATROPIA.—Sometimes sulphate of utropla, howevor neutral. Irritates the skin; could nny kind brother reader tell me the reason .'—Occlus.

[26d9.]—OLD COIN.—Whllo digging in the garden a short time ago, I found an old brass coin, abont the size of a halfpenny. On one side is a head rind some

letters; all lean make out are, VES-ASIANVS

AVC; on the other side la represented a tree, with a human figure on each side, one in a sitting aud one in a standing posture-, under these are the letters S C, and round it, —VDAEA CAPTA. Will some brother reader tell me what coin it Is, and if of any value /— X. 1. D.

[2S10]-ANILINE DYES FOR FEATHERS.— Will some subscriber to your excellent journal, inform me of the method for obtaining the colour known an Bismarck brown, for feathers? Detailed particulars of the process, or any other useful Information on the subject, will be thankfully received.—As Axateup. Dyer.

[2611.]—RK-GILDIKG BANNER—Can any of your readers Inform me how to gild or re-gild a silk banner,, such as used by Sunday schools In processions. I havetried by marking out the letters wltb gold size, anil then laying on the gold leaf, bnt the size penetrates through the Bilk, and makes the other side of tho banner look anything but neat. 1 bavc seen several banners, and the Impression of the letters does not penetrate through the silk, so 1 think I must have goo hold of the wrong process, although the person I got it from was a professional gilder?—Inquirer.

[2612.]-NEWARK'8 CEMENT.—Would any onebe so kind as to give me some Information about the above cement, used very much at New York for concrete building; hew is it made (if not a secret)-, if It has been, or is used in this country, and how is It sold! Any information would oblige.—John Hudson, Sunderland.

[2M3]-S0C1AL SCIENCE.—Will some brother reader kindly let me know If I could procure the pamphlets which aro printed after the Social Science meetluRS, and if so, to whom should I writ-.-? Could I become a member without being present at the meetings?—Thomas J. O'connor.

[2614]-WRITING ON GLASS.—What acid mint I use, so as to have the letters while when burned I in? Perhaps"Engraver"willkindlya8sist.—Tboma» J. O'connor.

[2i)15 ]-BICYCLE WHEEL—I should feel much obliged if some of your numerous correspondents would say whether if the rim were made of one piece of American elm, it would be stronger than If made in separate bits? If it would not bo thought too] much trouble, a drawing would be much prized.—Semper Vigilans.

[2016.]-WET RAGS—Would one of your correspondents supply mo with a simple and cbe.ip indoor method for drying wet rags, say to the extent of ouo ton per diem?—Dryer.

[2617]-GLYCERINE AND OLEIC ACID—Can any of my fellow readers tell me how glycerine anil oleic acid are made?—Experiment.

[2618]-TO '■ F.R. AS."—I feel obliged to "F.R.A.S." for his answers to my inquiries. I am sorry I did not describe my telescope sufficiently; it Is an 8Jin. ailverert glass, reflecting instrument, equatoreally mounted. 1 wished to know how to set it absolutely level, N r, S. r, K r, S, so that I should rind the declination of a star right according to Mr. Webb's book, iu whatever point of the heavens the instrument was pointed. It has all the motions necessary, but I do not know how to set about it, Ot where to begin ?—H. A, C

[2019.J-TO " TANGKNT."—Will " Tangent " oblUrc by giving a drawing and description of Khnmkorff» double mercury contact breaker for induction coil, and also say if 1 can use anything better than about five liycrs of gutt.-i pereha tissue to insulate the layers of secondary wire, the amount about lilb. of No. 8(.. I find a difricultv in gettitig the tissue to'lay flat and Btnooth; would a solution of guttapercha in bisulphide of carbon, laid on In Beveral coats, answer as welt as the tissue?—Vacuum Tube.

[2620.1-BAKTON'S BUTTONS.-Dlffractlon. say Sir J. Ilerschel's ("Familiar Lectures on Scientific Sub

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