acid. first of the hydrocarbon gases, and subsequently of the chlorine gas, are even more disagreeable to the analyst than the nitrous fumes evolved during the nitrohydrochloric acid process. 3rd. it is not so rapid as the nitrohydrochloric acid process. 4th. The results do not exhibit a greater accuracy than is obtainable by solution of the iron in nitrohydrochloric Mr. Hamilton, in his article, says: "I have analysed several specimens of pig-iron according to the solution in the nitrochloric acid method, with all due precautions, which, although exceedingly important, are often omitted in explanations of the process." As Mr. 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 in which I estimate sulphur in iron and steel by that method, having always found the results trustworthy and accurate. THE SOPER RIFLE. FIG.L ber, 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. have given references to the peculiar parts only; the others, as the barrel, cock, &c., are similar to the ordinary rifle. Fig. 1 represents a side view; Fig. 2 a longitudinal section; Figs. 3 and 4 are end views, with the breechblock raised and closed respectively; Fig. 5 shows the breech block. C. H. W. B. P.S.-Just at the moment of writing I hear another trial is to be made as regards rapidity of firing, which I hope to witness, and if more than 60 rounds per minute are fired, the Editor shall be duly informed. INGREDIENTS FOR GOOD PAINT. SIR,-In answer to "Surveyor," (qy. 2500), I may tell him the ingredients necessary to form a good paint are as follows:Ist. A genuine well gound material or paint proper for the body. 2nd. Siccaline or boiled linseed oil, as a vehicle for the convenient retention of the paint itself. SIR, Some readers may recollect a description of a rifle invented by Mr. Soper, in Vol. VII, p. 339. 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 the previous one. The former was rejected by the Small-Arms Committee for its seeming-I say seeming intentionally complication. The one I am about to describe is simplicity itself. By a very unfortunate decision, however, of the Government, the It may be necessary to say a few words regarding gun of which I give diagrams, has not been con- the extractor, E, Fig. 2. By the diagram it will be sidered in the competition, as it could not by any seen the end of the extractor is raised, and it is this possible means be got ready by the day stated as the part which catches the rim of the cartridge. The exlast when new inventions would be received. There- tractor is moved by means of a lever, and by a pecufore, for the moment, it has the cold shoulder, but if liar formation of the hammer it is started back with a rival inventors, experienced mechanicians, the most slow motion, which is gradually accelerated, and finished eminent engineers of England, France, Germany, and with a jerk. By this peculiar motion great force may A weighed quantity (about 3 grammes) of iron is the United States, give, as they have given, their be exerted upon the cartridge shell in starting it from placed in a beaker of about 800 cubic centimetres' capa- opinion that this rew gun is the best in the world, the barrel, which is necessary when the explosion of city, and having a clock-glass cover. 20 cubic centi- how long will it be before Government is compelled to the cartridge, or some other means, has caused to stick. metres of strong hydrochloric acid are mixed with 10 admit it in competition with others? The require-tightly in the barrel. One screw secures the whole. cubic centimetres of strong nitric acid in a small ments of a breech-loader are simplicity, strength, and The stock of the gun is in one, and, therefore, very beaker, and gently heated until the acid liquid assumes certainty of action, We will consider for a moment strong. a slightly yellowish tint. The acid is then poured, how far the gun we are discussing answers to these little at a time, into the beaker containing the iron, the requirements. Its constituent parts are reduced to a glass cover being moved just sufficient to allow of the minimum, and therefore, of necessity we get simpliacid being poured into the beaker. A very strong city. "The cocking of the piece, the opening of the reaction takes place, and great heat is generated; but breech, and the extracting of the empty cartridge the capacity of the beaker, and the large cooling sur- shells are simultaneously effected by one movement of face presented by it prevents any loss by effervescence. the hand without changing the position of the piece. The solution of the iron is thus effected in two or The breach is closed by a block which is hinged or three minutes, and the whole of the sulphuris oxidised pivotted at one side of the rear of the barrel, and to sulphuric acid. The sides of the beaker and the which is raised and turned laterally on its pivot to clock-glass cover are now rinsed by means of the open the breech" (specification). Fig 1, A, the breechwash-bottle, and the liquid is evaporated nearly to block is perforated to allow the insertion of the striker, 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 filtrate diluted to about 100 or 150 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, and the precipitated sulphate of barium collected on the filter paper; but it is importaat 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 his paper says:-"After filtering and washing it well with boiling 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 boiling 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, and if a trace of yellow colour remains in any part of the paper, a few drops of hydrochloric acid added, and further washing with cold water, will entirely remove it; the washing may then be continued with hot water. With proper care, and the observance of those precautions. the precipitate, when dried, ignited, and weighed, will be obtained perfectly white. On the other hand, if the paper be washed at first with boiling water, it will assume a 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 5 grammes of the metal and 50 cubic centimetres of the mixed acids. The weighings must be made on a balance capable of weighing accurately to the tenth part of a milligramme. I use one of Ladd and Oertling's balances, furnished with supports for the scale pans, and having agate plane and knife edges. The acids sometimes contain a trace of sulphurous acid, which 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 the weight of sulphate of barium obtained from a given volume of the mixed acids. Thus, if 60 cubic centimetres be the volume experimented on, and four milligrammes of sulphate of barium be obtained. then in a determination of sulphur in iron, using 3 grammes of iron and 30 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 nitrohydrochloric acid. In my opinion they are sufficient evidence of the accuracy of the method, and the difference between the results of the first and second analyses is in each case less than the differences obtained by Mr. Hamilton in his experiments: PIG IRON. 1st Analysis. 2nd Analysis. Diffence Fig. 1, B, by means of which the blow of the hammer FIG 5 3rd. "Patent" or other dryers, to assist the paint in hardening and drying. 4th. Turpentine or petroleum spirit, to give sufficient fluidity to the above mixture, so that it will work readily under the brush. It also acts as a dryer. The proportions of the above vary, (1) according to the nature of the paint, (2) according to the kind of surface to be covered, and (5) according to the weather. Speaking generally, and taking best ground white lead as an example, lcwt. lead, 6gal. boiled oil, 21lb. patent dryers, and 14gal turpentine, would make a paint suitable for second coat work. For priming or first coat, say 1gal. oil less, 1gal. turpentine more; this would cause the work to dry "dead" or flat, as is required. If the work is exposed to the weather, ask for outside Pale oak varnish is the best for grained woodwork. oak varnish. Unless you buy from a good house you will get varnish made with softer and cheaper guins; this is only fit for inside work. adulteration) is unmistakably apparent, or you have You cannot well detect adulterated paints unless the pure paint by you to serve as a standard. In this latter case, and taking ground white lead again as an Take, say, 50 parts lead to 1 part ground Prussian blue example, you may detect adulteration in this way: or vegetable black, mix together with a given quantity of oil and turpentine, and observe the shade of blue or grey. Proceed in the same manner with the sample to be tested. If this latter test gives you a darker blue or grey than the former, you may be sure that the latter is the most adulterated. By repeating the tests and diminishing the quantities of lead in the first sample, you may make both shades coincide. Note then the difference in the number of parts of lead to the one part of blue or black, and that will be your estimate as to the superiority of one sample over the other. This method may be adopted with most colours. The writer makes an oxide of iron paint that will stand this test favourably against any other he meets with. It is the method he adopts with every sample that comes within 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 use of petroleum spirit. Consumers usually buy paint in the ground or stiff state, and thin it themselves. If bought ready for use (a mode the writer would not generally recommend), the smell of 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 him further details. Being in the trade I do not wish further to speak of this subject, as it would make an advertisement of this reply. LLAH. وو WROUGHT IRON AND STEEL. 0.004 0-008 0.018 0-023 0-015 0.036 mainspring taken from an Enfield rifle, and a flat 1st Analysts. 2nd Analysis. Diffrnce of the utmost importance, the gun has many times trigger spring. Regarding strength, which is properly 11. Percentage of sulphur 0014 been fired with a charge of 200 grains of powder and 530 grains of lead. Lastly, respecting certainty of action, so simple and so certain is it that misfires are unknown in 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 been left for a fortnight under water, and during the next two weeks left out in the open air, recollect this was done during foggy Novem 12. 13. 0-012 EDWARD RICHARDS, Analytical Chemist to the THE ORGAN.-SOUNDBOARD, OR BELLOWS. SIR,-Having made the acquaintance of the ENGLISH MECHANIC 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 in which we were mutually interested, I need scarcely say that I have derived much pleasure in availing myself of a copy of his weekly visits ever since. I have felt much gratified in the perusal of his pages generally, and more particularly of late by an article on organ pipe construction, by," An Adept," whose very ample, clear, and minute instructions gave me encouragement to proceed at once in the construction of an instrument which, for a long period, I have been very anxious to commence. I have followed his instructions in making several experimental pipes (and very satisfactorily, 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," on page 609. No. 258, I had made up my mind to shelve the pipe operations for the present, and proceed with soundboard, or bellows. But here again I find myself in a fix; for, not knowing the scale or relative sizes of the pipes, I connot set out my soundboard: and again, as I wish the bellows to be just as large as my soundboard and windchest 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 G (medium scale), wood; 2, principal; 3, fifteenth; and 4, trumpet metal. And to this end I should esteem as a particular favour, answers to the following queries-1. In what number of the ENGLISH MECHANIC 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 for the diapason CC to F or G? 111 SIMPLEX. I WOOD PIPES VERSUS ORGAN METAL PIPES. DEAR "HARMONIOUS B.."-Glad to find the "gout" has not suppressed your defiant crow. always hoped wood pipes would come to the fore. "Adept" must be convinced by this time that metal is not a sine qua non for an organ. His communications, as original experiments, are of the highest value, and I hope he will arrive at speedy 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 organ may be rivalled in delicious wood, and I like to hear the tone and smell the fragrance of the goodly cedar. We can judge of good tone without the aid of the organ builders, just as we may pronounce upon 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 USSHER, B.A., M.B., Surgeon. EXTRACTS FROM CORRESPONDENCE. AMATEUR FARMING. -"A Country Vet." writes:-"Seeing a paragraph in your valuable journal whether it would not be advisable to give a column to questions and answers respecting the breeding, keeping, and rearing of horses, &c. I think myself it would be a good idea; but would it not be advisable to add to the abovementioned list that of dogs ahd poultry, especially as dog and 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 only too happy at any time in my humble position to render anything towards its advancement." REPLIES TO QUERIES. [1935.]-EQUATION. x + y + z = a+b+c bx + cy + az ex+ayay + bza2 + D2 + c2 [2007.]-TEMPERING DRILLS.-"S. T." is obliged [2234.]-COLOURED OBJECT GLASS.-SOLO. MON'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 eye-glass I refer to. I may here mention, that to each of the day eye-pieces I have pancratic tubes made, which vastly increases their power, both for earth and sky. By merely pull ing out this tube, a change can at once be made, from viewing the sun or moon in their entirety, to inspection of a highly-magnified portion of their surfaces.-AMATEUR. an to [2280.]-CHINA GRASS SEED.-The seed of Urtica nivea, 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. BLUE MAHOE WOOD.-"Joe" says:-"I enclose be [2286.]-GENEVA CYLINDER. - This is bought, as shown in Fig. 1. In selecting, 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, and then the cylinder between two of the teeth; when the play the tooth has inside the 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 THE SPHERICAL FORM OF THE EARTH.-. be false, but just inside the roundings of the lips. It M. T. Tydeman says:-"There is one argument in is best tried (and a second measurement is usual) in a support of the spherical form of the earth, of an depthing tool, increasing the depth till the tooth falls eminently practical character that I have never yet fairly outside and inside, and fails to turn the cylinder. seen insisted on, but have repeatedly put to the test Proceeding to turn it in, the broken piece is placed at from the cliffs and shores. If looking towards the sea 2, Fig. 1, so that the end of its pivot is level with the on a clear day, a perfectly straight edge be held lower edge of the lip E, when the corresponding part some distance from the eye, and then of the old piece will show how much to shorten the gently lowered down so as just to graze the horizon arbor D. Remember always in shortening the arbors (where the sen and sky appear to meet), it will be pivots, and a slight wear in the process of turning in; to allow for the point to be flattened in finishing the readily perceived that the waterline is not straight, and taking as much into account in every measurebut convex, and that the rule and the sea, if the former is held perfectly level and steady, first touch ment. Place the part A (3 Fig. 1) on the point of the n the centre of the straight edge. This, I think, is how much to turn away for the shoulder the balance shortened arbor, and the end of the pivot will show 'occular demonstration, and is almost as good a proof is to rest on. 4, Fig. 1 shows how to proceed with of the earth's rotundity as its shadow on the moon. USEFUL WORK- Bernardin" writes: " To my the point marked on its rim ought to be in a position the lower position. Before rivetting on the balance, brother readers who may understand German, I recommend the following work (printed in Latin type) on the plate, when the wheel is acting in the cylinder. to correspond with the centre one of the three marked Chemisch-technisches Repertorium, herausgegeben von which can be effected by turning the balance round Dr. Emil Jacobsen, Berlin, R, Gaertner, 150 p., in svo. It on the cylinder till it does so. Fig. 2 shows how to issues every 6 months, and contains extracts, recipes, proceed in "new work." The balance cock, centre &c., from 105 foreign reviews, on bleaching, building wheel and cock, and 'scape wheel and cock being materials, dyeing, oils, varnishes, textile fabrics, screwed on the plate, invert the cylinder to be turned leather preparing, metallurgy, photography, chemicals, in; placing the surface of the lower plug on the sur&c., and, moreover, a bibliographical index of all face G of the balance cock, shorten the arbor till the that has been published on these matters in those re-point comes just below the 'scape wheel. (The cylin views: to be obtained, I think, at every German der turned in complete is shown nierely to facilitate.) bookseller's in London. Since the bottom of the 'scape wheel occupies exactly the middle of the notch in 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 comes exactly in the middle of the notch. Here the adjustments for the balance and 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 of 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 comes on the collet. With a callipers P P, the upper and lower endstones F F being off, take the height from hole to hole; shorten the other arbor and pivot it in. Placing the pivot in its hole, the lower endstone being screwed on again, and the balance cock slipped on to keep the cylinder upright, see if the notch is too high for the 'scape wheel; in which case shorten the pivot with 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 the '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. Prass it well down all round on the shoulder before trying for the height. Fit on the hairspring-collet Screw on the balance cock without the endstone, and DD also pretty tightly, and turn in the top pivet. 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 cylinder is bound, just free it. See that the balance clears the curb-key or pins and stud for the hairspring. Round up and polish the ends of the pivots, which will give the proper endshake, and rivet on the balance.-NOBODY. send him a sketch of my favourite form of circular [2338]-SAW TEETH.-In answer to "R. T. S." I and deal frame saw teeth, the segment of C saw teeth are drawn half size for 30" C saw, the deal saw teeth are the proper size and deptb for A speed saw table of 150 or 170, both are sharpened with the flat file, both top and gullet, with about as much lead as is shown in The way I get so much hook on my saw teeth is by the drawing. If "R. T. S." has a less speed than 700 or 750 he must not carry so much hook on C, saw teeth. spindle. I grind on the back of the stone, the saw means of thin grindstones, which I put on the saw quires tact and care, as the stones are easily broken.being laid flat on the table, having a small jet of water running on the point of contact. The operation reMILL SAWYER. [2370.]-PEPPER MOTH.-The following answer will perhaps satisfy" Pupa." The caterpillar of the Phalaena Bitularia is of a pale colour, and has at the back two black spots. It feeds and is found on the elms, birch, rose, and the willow.-A. TOLHAUSEN, [2426.]-PIG IRON.-"Ironworker" will find that pig irou, after having been stocked for the length of time he mentions, has little or no sand on it, whereas new iron is generally well covered with this substance. [2376.]-LIFTING SACKS. -I think the following arrangement of pulleys will suit "Rusticus." A power of 125lb. applied at P will keep 250lb. at Win equilibrio, and if the power be increased it will lift it.-W. H. THORPE, Reading. [2374.]-BREWING. — “A Reader of Old Books" gives "New Subscriber," incorrect information respecting works on Brewing. Levesque on Brewing," is published at BEAM been thus prepared (a small quantity of water is some- [2450.]-FASTENING PIN TO BROOCH.-I find [2451.] DIAMETERS.-TO "AMATEUR." Amateur" is not right in the way in which he set about finding the size of the sun." The proper way would be to estimate its size as seen by the naked eye, and then to multiply it by the power he has applied. Say the sun appears as Ift. in diameter to the naked eye, then with a power of 60 it will appear to be 60ft. in diameter.-SCORPIO. [2465.]- COIL "Induction" asks, is an inch spark from a coil containing 2lb. of wire as much as he can 218,, aud Donovan's work can be had in one expect? Thistis not near a proportionate result; he vol. for 3s. 6d. If New Subscriber is in London, ought to get about double that length, and as the and will call at No. 20, Hop Exchange, South-faults of coils generally lie in the bad insulation of wark-street, he can see copies of all the works in print the secondary, I should advise him instead of adding on the subject.-W. L. more wire, to make perfect what he has done by wind[2382.]-STARTING VALVE.-I think the following the wire again, and taking greater care with the ing form of starting valve will suit "A. W. T." It insulation. In such a coil the wire ought not to be was designed by myself some time ago. It combines brought nearer the vulcanite ends than in. Also a reversing apparatus and starting valve in one. When the 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 energetic in action, but at the same time there will not be the least smell.-A. E. TUCKER. STEAM. PIPES STARTING HANDLE σο [2465.]-COIL-The length of primary coil-viz., two layers No. 16, is rather vague, as given by "Induction," as he does not give either the length or the diameter. If the primary wire bears the 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, 1in. It is a point often lost sight of in making coils, that their action (as their name denotes) depends on the principle of induction, and when this is taken into account, it is evident that the ultimate result of the slide A is in the position shown in the engraving, the secondary coil must be in exact ratio to the cause, the steam flows from the steam-pipe, through the hole-i.e, the primary coil and core. If the proportions are in the slide, and through the hole B in the block to right, I do not think it would be of the slightest use the cylinder. Now if the slide be brought forward so to add more wire, but I should be better able to judge that the other hole in it is opposite the hole C, the if I had the length of the primary wire given. I engine will be reversed. But if the slide is put in the have recently been favoured by M. Faurr, with one of middle the steam will be shut off. D is a plan of the his newly invented batteries, which I hear has been face of slide, next the steam-pipe. I have made two tested in competition with one of Groves's. In the holes in it, so that it shall not have to slide far either former case, the galvanometer needle was deflected 390, way, and consequently take up less room. If "A. and in the latter 40°, while the permanency was in faW. T." adopts this plan, I should like to know if he your of the former by some hours. Its construction is as makes it answer.-W. H. THORPE, Reading. follows:-In place of a platinum plate, we have a vessel [2430.]-FROM MR. G. BATES.-It would hardly made like an ordinary ginger beer bottle, but instead become me, as Messrs. Hopkinson and Co's agent, to of earthenware, it is made of some plumbago compoanswer your Leamside correspondent's questions in sition, this is filled with nitric acid, and the mouth is the manner suggested by him. The best answer I can stopped with a carbon plug, into which is screwed a give is, that several of the valves are now in working binding screw of ordinary construction; the bottle is operation at Leamside, which place I pass through placed inside a zinc plate, bent to encircle it, and the weekly, and if he will be good enough to send me his whole is placed in an ordinary round battery jar. The address I shall be glad to explain the working of the fluid used in the outer cell is common salt and water. valve personally to him, and also fix him one on apIn use, this battery gives off little if any fumes, is cheap proval free of cost, which is our usual way of doing to work, and may be obtained at Elliott, Brothers, business.-GEORGE BATES, Engineer, Eastbourne, Charing-cross. I do not find the fumes from Groves Darlington. battery at all inconvenient, as it can generally be wires covered with gutta percha, carried through a easily placed outside a window, and the connecting small crack left between it and the sill into the room to the coil. The 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.-T. S. CONISBEE. [2435.]-PROJECTION.-Proceed as in No. 2376, up to finding the line a N; then on any line take mk and nk, equal to A N and a M, and draw kl perpendicular to m k and equal to a a'; join m and n 1, and set off lo, pl, and a' e', equal to 1, the side of the cube. Draw og and pr parallel to lk, and set off b a = qk and d a equal to v ; then a projector from e' will mark off a e on the plan, and projectors from c and d on the plan, will mark off c' and d' 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 No. 2376, 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 Bernardin;" indeed I believe these are about the shortest and simplest solutions that can be given to these problems.-T. BROWN. while afloat, but the tenacious adherence of barnacles, seaweed, and slime, renders all such efforts futile. PATIENCE AND PERSEVERANCE. [2471.]-SUMMER BEVERAGE-LEMONADE.— Pour one pint of boiling water on 1lb. loaf sugar, dissolve the acid in a little of the liquor in a teacup, foz. citric acid, two pennyworth essence of lemon, 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 a piece of muslin ora wire strainer into a decanter; it will keep for a long time; mix it as you would greg. It a little more water is used it will not matter; it will not be quite so strong. Tried and approved. Some think a dash of wine or brandy is an improvement.-GROCER [2474.]-APPOLD PUMP.-The makers publish the sizes of the pumps, and the particulars of the quanbut they do not give the number of revolutions the tity of water thrown; sizes of pipes required, &c., themselves, for what reason I do not know; I have pump requires to make, which I believe they keep to adduced the following formula from experience. For instance: class 1, 6" diameter, class 2,8" dia, class 3, 12 diameter, and so on: The useful effect is said to average about 70 per cent. Molesworth's formula is very incomplete, and requires the divisional number as above to suit the dif ferent sizes or diameters of the pumps.-Nr. [2479.]-MUSIC.-" Clerk " having eng red music plates, had better send them to some litho music printer, who would transfer copy of same on to stone. This process is much cheaper than printing from the plate, and far better in appearance.-ZETUS. [2482.]-FUEL FOR PORTABLE ENGINE.- I have never found that coke of ordinary quality inin fact, from the relative cheapness of the two fuels, jured the fire-box of a portable engine more than coal, coke is more economical, even supposing that the fire box were more rapidly deteriorated by its use. scriber" will, however, find his tubes require cleaning out more frequently when using coke, owing to the 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, and the difference between coal and coke would be so small, as hardly to admit of being described as a percentage. -T. S. CONISBEE. "Sub [2485]-GALVANIC ENGINE.-I beg to inform "Old Salt" that the electro magnetic engine which he wishes for information about was invented by Professor Jacobi, 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 the other movable. The 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 inagnets 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 centres of the magnets had passed each other, the current was changed, so that the poles became of the same kind; and therefore they repelled each other, and thus rotation was produced. I never saw a detailed account of the above invention, and this account which I send is mainly taken from Lardner's Electricity(and Magnetism." 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 exknow of the matter, the less probability I see of any perience in electro magnetic engines, and the more I practicable application of electro motive power as a substitute for steam.-HENRY CHAPMAN. My own [2497.]-FROM "A THINKER-In answer to "Corstant Subscriber," the width of frame at seat is 20in.. the width between the centres of tiers of grinding [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 fit over the necks of the cylinder, which pletely fills them up, the sheathing is then applied 19in.; extreme breadth of ditto, 11in.; foot treadle 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 i have found to answer best for fixing the caps on to a cylinder is made of a mixture of about 1lb. of resin, 3oz. beeswax, and a small quantity of red ochre.HENRY CHAPMAN. [2442.]-MOUNTING LARGE CYLINDERS. Cylinders for electrical machines are generally mounted on wood axles, never metal ones, and as the hole 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 that 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. S. CONISBEE. [2446.]-MEAT PRESERVING.-The simplest way of preserving meat in tins for a long voyage, consists in placing the required cominodity in a tin case. soldering on the lid, leaving merely a small orifice unsoldered. When a sufficient number of tins have [2466.]-SHEATHING IRON SHIPS WITH COP- Copper and Muntz metal seem -- The 2499.J-APPARENT ANOMALY. My inquiring friend is quite correct in stating that the avoirdupois weight contains 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.]-WEIGHT OF WATER-A cubic foot of rain water, when the barometer stands at 29-5 metres, weighs 1000oz., or 62.5lb. Sea water = 64 14lb.SENEX. eet). PBIL 29, 1870.] ENGLISH MECHANIC AND MIRROR OF SCIENCE. 2509.-PUMPS -You cannot raise 4000 gallons of water (or 64 cubic feet per minute) with a fall of vater Sft., and only 50 gallons per minute (or 8 cubic The ram would be quite inadequate.-SENEX. The caterpillar of A. 12510.)-PEPPER MOTH. Bitularia is ground colour various from almost putty colour, some with green tinge and some tinge of red On each side of 5th, 6th, 7th, 8th, 10th, and brown. 11th segment is a reddish-raised spot, and there are two such spots on back of 9th and 12th segments. It feeds in August on acacia, lime-birch, oak, and It turns to a chrysalis in the ground in September, the moth comes out in May; The above is taken from Newman's The "Illustrated History of British Moths." £1. best work I ever saw.-A. NIOBE. many other trees. not common. 12519]-VULCANISING INDIA RUBBER-The apparatus used by dentists will do for vulcanising of any kind. The smaller the proportions of sulphur in the rubber, and the lower the temperature used, the softer and more elastic will be the india rubber. About 10 or 15 per cent. of sulphur, and a temperature of 270 or 275° for 4 hours, will make an elastic rubber. W per cent. of sulphur and a temperature of 315° for 2 hours will make a hard vulcanite like ivory.-A DENTIST. in 1 guart of water. 12-WATERPROOFING PAPER.-To waterproof packing paper, dissolve 1lb. of white soap In another quart of water 1 ounce of gum nitric, and 6 ounces of glue; e two solutions, heat them and soak the paper quid then hang it up to dry. From "The Best ything."-BUSY BEE. which I give, and he has merely to fold a sheet to take different sized sheets of paper, the dimensions of surement of any sized book he is likely to meet in the in either 8, 16, 24, 32, 36, or 64 pages to get at the meaordinary course of life. If I had a rule and the books handy I would give the dimensions he asks for; reduction should of course be made for" trimming but I think I have made it sufficiently plain. A slight edges, but that again is compensated for by the covers of the book. Sizes of sheets of paper :-Imperial, 30 by 22; super-royal, 28 by 20; royal, 24 by 19; medium, 33, by 18; demy, 22 by 17; large post, 21 by 16; post, 19 by 15; foolscap, 17 by 134in. With these dimensions given it will be easy to fold up a sheet to any required size of page and the measurement will then be plain enough. But if "F. F." cannot understand, and will let me know, I will" try again.' -SAUL RYMEA. W. [2563.] SMALL COPPER COIN. The great scarcity of halfpennies and farthings, coined by copper and brass pieces called "tradesmen's tokens."' government, led to the issue, about 1648, of the small They were struck, as their name indicates, by private These latter were usually tradesmen, for the use of their customers; and also, but more rarely, for the use of a whole village, borough, town, or city. called" town pieces," and your correspondent's coin is one of them. It is engraved in Snelling's "Copper Coinage," plate 1, No. 32, and is most likely a halfpenny struck by the corporation of Dover.-HENRY [2563.]-SMALL COPPER COIN.-This copper coin HENFREY, M.N.S., &c., &c., Markham-house, Brighton. was probably issued by the town authorities of Dover, such coins, or tokens as they are more correctly termed, being very numerous at that period. The design on the rev. is described by Boyne in his list of the 17th century tokens, p. 130, No. 160, St. Martin on following him." To which is appended the following horseback, dividing his cloak with a beggar, who is note:-St. Martin in Roman Catholic times was patron, Saints of Dover, and the Church of St. Martin-leGrand the mother-church. Amongst its other privileges was that of beginning service before all the other churches and chapels in the district. on the tokens on the Borough Dover Fair is still called St. Martin's Fair. The church was destroyed at the time of the Reformation, Counter-seal which dates as far back as the year 1305. This has been described by Browne Willis as same device is "a highwayman robbing a man on foot."-D. T. BATTY. "bricks." and I therefore venture to contribute mine. suggests that we (your readers) should bring our teries, with a view to economy and constancy, toI have always considered the study of galvanic batgether with intensity, as most interesting and most important to science in many directions, and I shall They will be mentioned endeavour to describe (briefly) those batteries which I consider the most useful. under two heads, first, single fluid batteries, and second, double fluid ones; amongst the first there are Cruikshank's, which consists of plates of copper and zinc, cemented into a wooden trough and excited by a weak solution of sulphuric acid and water. This battery, although a most important improvement at the time it was invented, is now entirely superseded. Smee's battery is a very useful arrangement for experimental use if it is not wanted to be very constant, or to be kept in action for a long time. The construction of it is as follows: There is an earthenware vessel to contain the exciting solution, which consists of one part sulphuric acid to about 7 of water. The negative plate is made of platinised silver, and that is held in a wooden or gutta percha frame between the two positive plates, which are made of zinc. By far the most powerful battery that I have seen or used is one invented about 1852 by Mr. Martyn, J. Roberts, both as regards constancy, intensity, and quantity. It consists of an earthenware pot to hold the exciting solution, undiluted nitrous acid, the positive plate is made out of pure tin, and it is placed between the two negative plates, which are made of pure platinum. I have used a battery of that kind continually for many able to detect the slightest variation in the current. consecutive hours, for the electric light, without being The disadvantages are the cost of construction and CURIOUS AFFECTION OF THE TEETH. working, and the large quantity of fumes evolved from is is only a deposit of tartar from want of clean- the nitrous acid. There are several other kinds of single Wine is on the teeth at present must be care-fluid batteries, but those I have mentioned I think are the most important of them, and I now pass on to Daniel's constant battery contussy cb oped off with a fine thin-edged instrument, but at an angle near the joint to enable it to be got the double fluid kind. into any crevice with ease, and the teeth must be kept sists of a copper vessel, which at one and the same clean afterwards with a strong rough tooth brush and time holds one of the fluids (a saturated solution of If the tartar is sulphate of copper), and forms the negative plate. camphorated chalk and water. chipped clean away and the teeth kept clean the gum Within the copper vessel is placed the porous cell, and in that is placed the positive plate, made of a thick will grow up again in a week or two.-A DENTIST. This battery is a very convenient one [25241-LONGITUDE.-Difference in time between rod of zinc, and the other fluid, 1' of sulphuric acid Belfast and Glasgow, 6 min. 40 sec.-D. B. The Maynooth battery, invented by Pro[2526.-SUBMARINE LAMP.-No lamp could be from the constancy of its action and the absence of Every miner fumes. "red" with air by a single tube. knows that to obtain a proper supply, a current must fessor Callan, is a very powerful, but a very un[2564.]-LEADEN COIN.-Is probably a token of the be established by means of a "down cast" and "up pleasant one to work with, on account of the nitrous cast" shaft. This could be effected without much fumes given off from it. It is arranged as follows:be of that period, but cannot bring any authority to difficulty in the case of Mr. W. A. Hackett's lamp, There is an outer vessel made of cast iron, which Groves's bear. I shall be equally obliged with "Old Coin" which may be taken to represent a mine on a small forms the negative plate, and holds the one fluid (un- time of Elizabeth. I possess similar ones reputed to scale. But common india-rubber tubing will not do, as diluted nitrous acid), in other respects the arrangeit would be throttled by the pressure of the water. "H" ment is the same as the preceding one. [2566.]-TOOTH-POWDER.-Camphorated chalk is must get some tubing kept disturbed by a coil of wire battery is one of the most useful, I think the most. It for any authoritative information upon it.-D. T. This is enough on the is made as follows:-An outer cell of earthenware BATTY, 9, Fennell-street, Manchester. inside, such as the divers use. general question; but if Mr. Hackett has any practical and an inner porous cell; the negative plate is made object in view, I shall be happy to supply him with of platinum, and the two positives are zinc, the fluids very good, and economical as well. The following is used are, for the negative plate in the porous cell pure also recommended:-Orris root,ounce; gum myrrh, nitric acid, although I think nitro-sulphuric is better.ounce; nutmeg, finely powdered, 1 scruple; chalk 1 ounce; mix. Proved.-BUSY BEE. The fluid for the positive plate is 1 of sulphuric acid to 6 or 7 of water. Bunsen's battery is similar to Groves's, 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 aluminium instead of platinum for a negative plate, but although I got a fair current from it, I did not consider it at all equal to Groves's, and one thing fatal to it was that the aluminium was slowly dissolved by the nitric acid, and I therefore discontinued to use it. In all the above arrangements the zinc is amalgamated with mercury.-HENRY CHAPMAN. NAMES ON PLANS.-A [2547.]-PRINTING further details.-THICLORIUS. [2534.)-SOLUTION WANTED-If "Minnehaha will draw the figure of his problem, using the same letters as in his query, and join DE, he will find that, since A C=2E C, and B C 2 C D, and the angle A C B is common to the two triangles AB C, DCE, A B = 2 E D, and the angles CED, CDE = CAB, CB A, respectively; therefore D E is parallel to A B; therefore the angles B E'D, ADE A BE, BA D respectively; therefore the triangles A B G D G E are similar; and AG: DG:: A B : DE:2:180 that AG2 D G.-HUGO. E A B very pretty and easy method 12345 [2549.]-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 hori zontal one.-HENRY CHAPMAN. [2555.]-ECHO.-An Ayrshire amateur can produce NARDIN. [2561.]-BOOKS.-The following dimensions are, I believe, correct :-Imperial 8vo., 11 by 7; super, royal 8vo., 101 by 63; royal 8vo., 10 by 6; demy 8vo. 8 by 5; post 8vo., 7 by 2; crown 8vo., 7 by 5; demy 12mo., 7 by 43; royal 18mo., 64 by 41; foolscap 8vo., 63 by 44; imperial 32mo., 54 by 3; deay 18mo., 5 by intersect at G: show that A G is double of G D-3; foolscap, 12mo., 5 by 31; royal 32mo., 5 by 3 demy 32mo., 4 by 23; demy 48mo., 3 by 24in.; edges making figure. I have triangle C D E sim. to C B A (Euc. vi. 6) triangle D G E sim. to BGA (Euc. vi. 4) [2539.]-OKE. A Turkish oke is as nearly as possible equal to 2lb. 12oz. avoirdupois. A kilogramme is about 1lb., so there is not much difference.-EDARDUM A. [2539.]-OKE-A Turkish oke = 127848 grammes =2,82861b. avoirdupois. Local okes vary sometimes. [2561.]—SIZES OF BOOKS.—It is almost impo3- 39 The [2577.]-BORING GLASS.-"C. H." can bore a hole or scratch a ring, of the size and in the place required in his glass sheet, in the following way: Let himmark on each side of the sheet. These rings will, of course, exactly correspond. Then let him mark out a series of points pretty near each other, round the circumference 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 glass sheet horizontally with one of the circumferential points, steadily resting upon the upright punch. Applying his own punch to the same point on the upper surface of the glass, and using gentle blows of the he will soon work his way down through the hammer, sheet, until the two punches meet, leaving a small perforation without causing the slightest (unless he is clumsy). Repeating the process at other points, all round the circle, he will find at last that the included disc can be readily kuocked out by a slight tap, leaving the required hole; where rough edge, can be amoothed off by file.-MECHANICUS. "stal FILES SHARPENED BY GALVANIC CURRENT.-A very interesting and economical process for re-sharpening files has been exhibited before the Société d' Encouragement of Paris by M. WerderWell-worn files are first carefully cleaned by mana. means of hot water and soda; they are then placed in connection with the positive pole of a battery, in a bath composed of 40 parts of sulphuric acid, 80 parts of The negative pole nitric acid, and 1000 parts of water. is formed of a copper spiral surrounding the files, but not touching them; the coil terminates in a wire the result of practical experience. which rises towards the surface. This arrangement is washed, and dried, when the whole of the hollows will have been ten minutes in the bath they are taken out, manner; but should the effect not be sufficient, they be found to have been attacked in a very sensible are replaced for the same period as before. When the files RESTORING LIFE.-In consequence of the experiments of M. Labordette, the National Lifeboat Institution has decided on omitting from its new instructions the statement that among the appearances which generally accompany death the "jaws are clenched and the fingers semi-contracted." Dr. Labordette's experiments on animals, have clearly proved that in nine of twelve cases, after clenching of the jaws, &c., had been observed, life had been restored; and has He has given several instances of human beings having been resuscitated under similar circumstances. 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 immersion, indicated remaining vitality, and that the same should enconrage perseverance in the efforts to restore life. NOTES AND QUERIES. [2580.]-LARGE TELESCOPES.-I would ask some correspondent who can give a reply, if he knows where it is possible for a working man like myself, 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 17in. aperture, which will divide double stars as close as 34"; for instance, and Bootis, Aquarii Pegasi, but when I read the accounts of astronomers, and what they have seen with their gigantic telescapes, I long to see some of the wonders they describe. Some years ago, I believe, Mr. Slater, the optician, used to exhibit a large Equatoreal at his house in the Euston-road, but it has now disappeared. Two or three street telescopes, of 4in. or 5in. aperture, I have looked through, but not one of them was of any account?-G. F. [2581]-GUTTA PERCHA SHOES.-Will some of the obliging correspondents of our journal, favour me with information on the following queries? 1. Are gutta percha shoes injurious for the eyesight, if so, why? 2. Which way shall I proceed to re-sole an old pair of gutta percha shoes? If possible, state price of the material (gutta percha), and how sold?-D. E. WILLIAMS. [2582]-WEIGHT OF FRUSTRUM, &c-A frustrum of an iron cone has a height of 12ft., the diameter at the smaller end is 2ft., and at the larger end 4ft. A cubic foot of iron 410lb.; 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 the height of the frustrum left?-O. 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 inform me if it is best, previous to driving 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 fun directions for charging the battery, also if the zinc should be amalgamated, and how much lead should be put into a 6n. porous pot; by so doing, he will much oblige, as I have the materials ready, according to directions given in Query 2184 ?-CARFAX. obliged to any reader of the MECHANIC, who may have [2594.] BORING WOODEN HANDLES IN [2596.]-BUSY BEE.--Could some of my fellow sub- [2598.]-ELECTRIC.-Will "Sigma," or some other trisecting the angle, La is marked off from F or w In dividing the angle into five equal parts, M Fis into seven equal parts, N T is marked off from Kon marked off from H on B H, and in dividing the angie B K, &c., &c., whilst the distance S E, marked on the last arc, remains the same for all divisions of the angle.-Y. P. W. [2006.)-DAWN, &c.-What countries have the WILLIAMS. longest dawn and twilight, and why?-DAVID E. any reader give me some practical instructions for: ating [2607.]-HEATING GREENHOUSES.-W a small greenhouse, say 10 x 4? I have read all the notes recently inserted, but they do not contain anything sufficiently detailed. I want particulars of cost requisite, economy, and durability, are essential desiof the various methods. The small amount of attention dorata. Does any one know anything of Kassett's system? Information will be useful to many besides. SAUL RYMEA. sulphate of atropia, however neutral, irritates the [2608.)-SULPHATE OF ATROPIA.-Sometimes skin; could any kind brother reader tell me the reason?-OCULUS. [2000.]-CLEANING OF DIATOMS.-Will any of BEATEN. I should size of a halfpenny. On one side is a head and some [2609]-OLD COIN.-While digging in the garden a short time ago, I found an old brass coin, about the letters; all I can inake out are, VES-ASIANVS... human figure on each side, one in a sitting and one in AVC; on the other side is represented a tree, with a a standing posture; under these are the letters S C, reader tell me what coin it is, and if of any value?and round it, -VDAEA CAPTA. Will some brother [2810]-ANILINE DYES FOR FEATHERS. Will some subscriber to your excellent journal, inform me of the method for obtaining the colour known as the process, or any other useful information on the Bismarck brown, for feathers? Detailed particulars of DYER. [2601.]-VENUS.-On the 1st of November, 1871, Venus will be at her greatest brilliancy; will" Omi-subject, will be thankfully received.-AN AMATEUR cron," 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. :— (r + + R) (~ + ( − R) 1343 [2585.]-FLOCK PAPERHANGINGS.-I should be obliged by any one practically acquainted with the manufacture of paperhangings, to inform me how "flock" paper is made; also, if the gold patterns on same are printed on the paper before or after the flock is laid on? Information in detail is sought.-ZETUS. [2386.]-WHEEL MAKING.-Will some brother mechanic give me information relative to the best kind of machinery for forming carriage or cart wheel spokes, and any other part of wheels?-INQUIRER. [2587.)-CHINA GRASS.-Can any of my fellow subscribers inform me where I can get a small quan-9-9965. tity of China grass ?-C. KATKA. [2588.)-EQUATOREAL MOUNTING.-I should feel obliged it "Hyperion" would answer my query respecting his mounting, No. 1792, in No. 256, Vol. X. -NEPTUNE, No. 1. [2589.-RAISING WATER-With respect to my former query, respecting raising water, as "Machinator" did not seem to understand me, I will try to explain myself more fully. I do not want the water raked to the dam above, as he seems to think, but to supply a cistern with fresh water. It is not needful to be a continuous stream. I want it from a mill tail, so a not in any way to interfere with the working of the water-wheel. It will require to be raised 8 or 10ft. Figh, but no particular quantity.-NEPTUNE, No. 1. [2590.]-BOOKS WANTED.-Can any of my fellowcaders tell me the names and prices of any works now published, on the construction and details of small engines, from 1 to 3 horse power, either vertical or horizontal?-E. B. [2591.7-FLYING MACHINE.-I wish a model of a flying machine; could to make brother reader give me the following information? some kind How much gas in a bladder would it require to raise 3oz.? What kind of bladder would be the 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 Mr. Blacklock or Mr. Purkiss, be so kind as to say whether it is necessary to use a dew-cap with a reflecting telescope (aperture 6in.), 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. Where R radius vector of the earth = 9919, its log. = [2611.)-RE-GILDING 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 have tried by marking out the letters with gold size, and then laying on the gold leaf, but the size penetrates through the silk, and makes the other side of the banner look anything but neat. I have seen several banners, and the impression of the letters does not penetrate through the silk, so I think I must have got hold of the wrong process, although the person I got it from was a professional gilder?-INQUIRER. [2612]-NEWARK'S CEMENT.-Would any one above cement, used very much at New York for conbe so kind as to give me some information about the crete building; how 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. [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 work is in existance, will some fellow subscriber give publisher's reader kindly let me know if I could procure the [2613.]-SOCIAL SCIENCE.-Will some brother name and address, and title of book ?-J. JONES. pamphlets which are printed after the Social Science [2604.]-PROBLEM.-I beg to thank Mr. Tolhausen meetings, and if so, to whom should I write? Could and Mr. Biggs for their replies to my query I become a member without being present at the (2180), in last week's and this week's MECHANIC. meetings?-THOMAS J. O'CONNOR. Would some of your mathematical correspondents kindly give me a few hints as to the solution of the I use, so as to have the letters white when burned [2614.]-WRITING ON GLASS.-What acid must following, which I extract from the Science and Artin? Perhaps "Engraver" will kindly assist.-THOMAS Department Examination papers a year or two ago? J. O'CONNOR. Two points are 2 and 2.5in. from the centre of a circle eircle which, passing through these two points, shall of lin. radius, and 3in. from each other. Draw the touch the 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 ease of the acute angle, does not the point page 89), as described in the case of the obtuse angle, but in the fall on the outside of BA? I make it so. In that case and the arc described from B with B D + D2 as radius. I suppose the distance F P would be added to B D, Would not the same principle apply to the division of angles into any number of equal parts, with this [2593.]-DEFECTIVE BATTERY.-For a number be divided into five equal parts; on B C mark off five difference-viz., Suppose the angle A B C (page 89), to of years I have been unable to labour through ill equal distances, proceed as before; mark off the dishealth. For several month I have been using one of tance H L on the fifth arc, join the fifth point with B, Smee's electric machines, and feel slightly better. It and where this straight line cuts the arc E H (say in went well for a time, but of late has been going very the point ), mark off E from the fifth point on BC, feebly, the vibrating often stopping. Occasionally it and proceed as in the other case. Again, suppose the would go a few minutes or seconds, if the finger were angle ABC is to be divided into seven equal parts; gently pressed on the screw above the vibrator. Recently, when trying to discover what was wrong......I K, draw the arcs LD, ME, NF, OG, PH, on BC mark off any seven equal distances, BD, DE with it, two of the zinc plates got loose when in the 2 I, and R K, bisect the angle ABC by the line B X, acid, and in trying to tighten the screw, the silver cutting M E in S, mark off the distance S E on the are plate bent and touched one of the former, producing a R K from the point K-viz, the points 1, 2, 3, 4, 5, 6, hissing sound, whitening and thickening the acid. removed it as quickly as possible, and straightened from the point K mark off K V, equal to N T, and from I and 7; join 7 B, cutting the arc NF in the point T, and fastened it properly. Since then I can get no B with BV as radius, describe the arc V U, and the vibratory action, whether from the above cause or distance S E will divide the arc U V into seven equal not, I cannot say. The zinc plates were amalgamated parts, whence the angle A B C is divided into seven immediately before it stopped. I put in fresh acid (1 equal parts as required. On seeing the article on the to 8 of water), but this brought no improvement. Per- "Trisection of an Angle," in this number of the MEhaps the silver plates require platinising. May I ask CHANIC, it struck me that by a somewhat similar if they are done with the same material (mercury), and method, an angle might be divided into any number in the same way, as the zinc plates? I would be truly of equal parts, and I have thus attempted it in the would say whether if the rim were made of one piece of obliged if some of your numerous correspondents [2615]-BICYCLE WHEEL.-I should feel much American elm, it would be stronger than if made in separate bits? If it would not be thought too much trouble, a drawing would be much prized.-SEMPER VIGILANS. spondents supply me with a simple and cheap indoor [2616.)-WET RAGS.-Would one of your corremethod for drying wet rags, say to the extent of one ton per diem ?-DRYER. [2617]-GLYCERINE AND OLEIC ACID-Can oleic acid are made?-EXPERIMENT. for his answers to my inquiries. I am sorry I did not [2618.]-TOF.R.A.S."-I feel obliged to "F.R.A.S." describe my telescope sufficiently; it is an Sin. silvered glass, reflecting instrument, equatoreally mounted. E, S, so that I should find the declination of a star wished to know how to set it absolutely level, N r, S. r. 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 ses about it, or where to begin ?-H. A, C. any of my fellow readers tell me how glycerine and I by giving a drawing and description of Raumkort |