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ha? a draw box, and n draught of about 4, Иск ho can handle it pretty ütroag. as the fibre« aro already «traishtened ready for drawing. But if he hae no draw-box to M« engine, or only one with a draught of s-iy 1-25. if be will examine the sliror. he will find the libres all wave, and it will be seen that under the above clreumstanc'JB it would be foolishness to subject it at once to a great draught» thereforo it should Le -coaxeá" straight. Under these circumstances, •' Factory Lad" will find the following the best distribution of hie draught ¡—Between back and -Ird, 125; between 3rd an4.2iid, 1S7; and between 2nd and front S; V>t»l. e-90. , ,

"B. W. " Rochdale, talks about a draught between Ian Ro.t feed rollers. Now there le not—or rather, ouah! not to be—any draught at all there. What use would it bef The lap should be delivered just as the feed rollers want it. neither slower nor faster. "B.W." must bear in mind thore Is no draught between tbo dorter and delivering rollers, but a contraction.

llARMONioua Cotton Spinner.

Sib—I have road a letter on "Cone Koving Frame»," in April 22. "B. W. li." says It is immaterial whether tbo bobbin leads the flyer, or the 1lyer lt-ads tue bobbin; I f that be true, I should like to know the object of the frames being made to gear in that f,.rm which appear» to be the general rule according to a Mr. E. Slater, April 20, page 133, If there be no advantage In tlie make of the thread by running the 1юЬЫп quicker than the flyer lu mv opinion it is n disadvantage to the wear and tear of the machines, beside» taking more power to run the bobbin 11 to I, than would be required to run it 9 to 1 of the roller. My roa*ou for eeekiDg information is because I have been a worker of cone frames 10 or 12 yeas». I n Taylor Wordsworth's make for worsted, the gearing is во arrain»¿4 that the liver must lead tho bobbin. .Multiply the diamewr of delivering roller by the revolutions per minute; for a dlvldond divide by tho diameter ot bobbin, the quotient subtracted from the speed of spindle per mínate will give tho number of revolution» the bobbin will make Der minute. Since 1 read "B. W. R s " remarks, thinking there was something in the make of the thread. I tried to run tho bobbin quicker thau the flyer, but on account of the gear I could not. K. Halmsiiav, (jomersal.

Sm.—lt I am not mistaken. "Mutual Improvement,"

£age Ш, Intended tho question propounded by him to ) somewhat ambiguous, as the rule he quotes cauuot be "strictly correct," because it takes note of no draught in the carding englue, save that between the "iced rollers" and '' doffer," although there are two other draughts outside it; so that obviously, the draught of the eugiue must be the total ef the three. The first draught is between "lap rollor " and " feed roller«-," the second between "feed rollers" nnd "doffer" (for finding this one the rule is correct); l\e tliird, between "doffer" and "calenders." There formerly was a "draw box" attached to each carding engine, for the purpose of adding to the draught of the engine a considerable amount—some havo [them still, because they are "penny wise and pound foolish." It may also be said of the draught of any machine, the theoretical draught is not often the working one, as the latter depends upon the qualities of the cotton, and varies accordingly.

A word now for ihs lads on the subject of draughts. The term, as used In cotton spinning,means the drawing out, into greater length, of the fibrous bands of cotton, by the rollers through which they раян in the process of manufacture. The cause ot this drawing out. or draught, is the accelerated surface speed that is given to each " line "or "row" of rollers in a set, from bock to front. Now, as you know, tho " top"

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and'* bottom " rollers seize tho cotton between their surfaces я» they revolve, ami draw it forward at the »ame rate of speed as they tht-uitelves are travelling, the back ones taking it in, or •• feeding," and the front one»» sending it out, or '* delivering " it. If, then, we wiah to find out how ranch longer the yarn, or »liver, ti being made by any sut of rollere through which it 1ч passing, or. in other words, if we wish to And the draught of the rollers, we havo only to find ont how much faster tho surface of the front one is travelling than that of the back one, by dividing tho epe*d of the quickest by that of tho slowest, and the quotient is the draught. Look now at the sketch, take the back roller to be lln. diam., and the front one to be 2in. ; as the front roller generally drives all the rest, yon must take it to have a wheel on tho end of It with 20- teeth, this drives a carrier of W teeth, which communlcatea its motion to the back roller wheel, with 20 like the front one. It will bo evident to you, that although the carrier has 00 teeth, it cannot give any greater or le?s «peed to the back roller than the speed of the front one, becauso it trauern its 1U given motion irom the same diameter it received

it, and the back and front wheels mnst both ганке an equal number of lurue in a driven time, because they have both the same number of teeth. What is moan I by "a given time" in tho time you might fix npuu if you were making an experiment, as one minute, two minutes, or any time you idease. Let us now suppose these rollers are making 40 revolutions per minute, how much farther will tlr; surface of the front one have travelled thau that of the back one? If we multiply the diam. of ä circle by 3'I4, we shall get as near tbo circumference of it as we require for our purposes, and the circumference of a circle is the distance it woul I travel if turned once round. Then lin. diam. of back roller, x 314 = 314ln circum,, and 3*14 x 40. tho number of turns = 125*60in., tho distance travelled by the surface of back roller, and consequently the length of yarn it would take in during a minute; and 2in. diam. of front roller x 3-.4 = ii-28in.. Its circumference the same as before, Q"2S x 40 = 25120in., the distance travelled by the front, one. Now if we divide the latter distance by the former, we evidently get the draught, as 25120 4- 12500 = 2, the draught of the rollers. They would draw out lin. into ilin. This example shows us that tho draught is the result ot surface speed, and not of speed of revolution, as both the rollers make tho same number of turns, that is 4». Again, the circumfereuce of a circlo is always iu proportion to its diameter, so that in this саэе we could havo found the draught by simply dividing tho diameter of the trout roller by that of the back one, seeing thev have a similar speed of revolution, аз 2-^-1 = 2. You will observe also, that the draught must not be called the differeuce in the speedH, although it is tho result of such difference, because the differánce between 1 and 2 = 1. as 2 — 1 = 1, or 10 — 6 = 5; but if oue travelled lOln. while the other travelled 5, the draught they would cause would lie 10 -r- 5 = 2, and nolo, which is the difference between 10 and 5. And further, suppose you wish to draw out 5 banks into 50 hanks, the draught required would be 50 —- 5 = 10, not 50 — 5 = 45. You may call it the geometrical ratio between the two travelling speeds, its measure being tho quotient obtained by dividing the greater by the lesser, lu a future letter, 1 will endeavour to make you understand the matter entirely. Perhaps some may think that 1 am treating the subject iu too simple a method; if so, I am not writing for such as they, but for the lads, and I know from experience that, to them, the more simply I speak, the more useful tho iutormation. There are hundreds and thousands of factory lad*, adults if you will, who, like myself, have not had the opportunity of attending a school, or at most, only for a few months at the time, when they were too young to learn anything that required study, or tho action of reasoning powers, and what may such as these do but pick up and sc.rat.rli off Information from anything they can? It the thing has too much weight in it, they cannot pick it up, and if it be too hard, they can scratch nithiug olí. The English Mechanic is doing a marvellous work, and judging from the common sense views of its Editor, and. the many gentlemen who contribute to it, it must go on working in the future until it comes to be looked upon ae one of tho little beginnings that has been developed for a good purpose, and carried out to a great end. The enterprise itself is the fulcrum, Its pages ore tho lever, ami all who will may take hold and sway down as much as thov can, until we are raised up from a state of chaotic ignorance, to one of scientific knowledge, if now, some of the kindly F.R.AS 's, who have such great strong hands, instead of being generous and courteous, wero to be thoughtless, and if, when they put their hands upon the lever, they crush and bruise the fingers of their less gifted brethren, so much that they made them tired of the good work, how unfortunate would be the result, and how contracted would be the sphere of its usefulness! Let the Mechanic, then, como to us like the sunshine, tempered so that the light it diffuses may be gladness in the high places, and health with happiness in the lowly ones.

Edward Habersham seems to have had an idea that the anomaly ho speaks of is not anomalous—no more it is. The avoirdupois pound contains 7,000gr., aud in weighing cotton, 24gr. make 1 dwt., but 20 dwte. do not make loz. He was mistaken. 1 think, when he said we are told so—4374gr. = loz., and 437$ x 16 - 7000. Have you been trying to work "Egyptian " and *' Surat " together, Edwaru, or avoirdupois and troy, eh? Let "Factory bad " page 136, divide his 7 by 3, and make the draughts of each lino of rollers in the drawing boxes equal, as 2-J ■+• ï| + 2fc = 7, or 2£ + 2J + 2\ 7. If lie is working "middling American" cotton, and "putting up" six ends, let him, if he can, reduce the toial lot-, and trot his rollers as near together as he can, unless their diameter be no more than the length of the staple.

E. Slater. Burnley,

Sir,—Tho question asked by а "Factory Lad" p. 136, on the proportionate draughts in a drawing frame with four lines of rollers, is one on which he will find much diversity of opinion to exist amongst practical cotton Bpinners. 1 williugly give my opinion, and hope others will do the same, although 1 know that in first-class concerns, where different systems prevail,

? »articulare of this bort are generally regarded of some mportance, and as secrets belonging to the business, not to be divulged to rival spinners. Whatever scruples there may be as to furnishiug information of this sort between individual firms, with я. publication such as the Mechanic, such scruples are inadmissible, and may be disregarded.

For a medium-stapled cotton, I should place the draughts as lollows :—

Between Front & 2nd rollers 2nd & 3rd 3rd & back

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DARK LINES IN SOLAR SPECTRTTH.

Sin,-In reply to Mr. Proctor, I cannot give any evidence based on my own observations of the dark lines in the spectrum, not possessing instrumental means for taking them, if he does, I fancy the question of their origin can be determined in this way. Suppose such a day as that described in my letter on p. 654, Vol. X., is selected for An examination, commencing with the sun on th« meridian. If the dark lines are broad and clear, and they diminish ns the sun descends tí) the horizon, we may safely refer them to solar absorption. If, on the contrary, they are narrow and indistinct, but widen out with the descent of the sun, then their terrestrial origin is plainly shown.

TA.

["T. A.'* says he cannot give any evidence "based on hie own observations." Does he not know that observation of phenomena is the initiatory step in scientific investigation? Why go on guessing and supposing1, without observing? If "T. A." would obiervc;first and infer nfterwords—record facts, and Uitin generalise, it would be botter for him and others. Л man like " T. A." may go on speculating on " if s," and fancying questions for a lifetime, and still be no wisor. For thousands of years, up to the time of Bacon, men—and great men too—proceeded as " T. A." does. And what did they do? Certainly not much. Wo mean nothing offensive when we state a million of men might pursue " T. A.'s " method for scores of generations, and Scjeueo would be nothing but a chaotic guess.—Ed. E. 31-]

DRILL FOR DRILLING STONE AND BRICK.

Sin,—I have sent you a rough sketch of n drill which 1 have uted for drilling stone and brick; it is an

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arm which you hold with ono hand to turn the drill whilst you strike with u hammer in the other.

A Country Lad.

PLUMBAGO v. PLATINA BATTERIES.

Sir,—In your last, T. S. CoaUbee refers to the nso of plumbago in tho place of platina as an aliment aud containing cell for the nitric aeid battery. I hope for the good of all of us interested, you will find space for my opinion on the merits of plumbago and platina. About 143 1 was experimenting upon the power ol various forme of batteries, both platina and carbon, and then discovered that the plumbago could be made the porous cell for holding trie acid. 1 hod several forms of them made, round and fiat, which gave great power for hours, n description of which was gtv.*n In the Practical Meclianic and Engineer's Magazine^ Vols. II. and III. The only difference between my arrangemenu and the newly-Invented one is the putting the stopper upon the old invention, thereby increasing iu defects. After years of experience, I am in a position to state what can be got irom plumbago or platina. First, plumbago, charcoal, or gas coke, all of which have been found to give a powerful current in contact with strong nitric acid, are by far the cheapest to get up, ami work well for some time; but, unfortunately, they get filled in their pores with a glut, get detached from their connections, or crumble down after drying, requiring frequent renewal aud repair. Now, as to pint ina, the first cost is somewhat additional, but if often used it soon proves the cheapest. And here I would advise all who wish to have a good powerful battery net to use the thinnest platina foil; get it somewhat stout; make the connections a short distance from the fluid with platina, coat well with shellac, uso the strongest nitric acid, saturated salt and water with the zinc porous tube, soft pipeclay, wood, or vegetable parchment, aud you have the simplest aud most powerful arrangement yet known.

A. Farquhxk.

THE BEDFORD CANAL EXPERIMENT—SIX MILES.

Siq.—As a correspondent has asked for some particulars respecting the above, I, having read all the correspondence, and tested the experiment on paper, will, with your permission, reply. In the first place, I may state that tho flat theorists cannot seem to comprehend the laws of gravitation aud the rule of tangents, together with thelaws of perspective. The first experimeut consisted of sighting from end to end with a 5-foot telescope, the line of sight forming a tangent with its centre in contact (to a sphere), the centre signal appeared approximately over 5ft. above it, thus proving that the three points were not in a straight line, but that by adding refraction, making 6ft, a curve with the radius of the earth would Intersect the three points. The diagram of this experiment was signed under protest by the globular opposer's referee, for what reason would appear strange to u« -vhö know the rule of three "boring sticks.'7 The next experiment consisted of sighting from end to end with a Troughton's level, the line of sight (in this case) forming a tangent with its point of contact at the first station. The centro signal (if reversed) appeared below the cross hair, and tbe end 'signal below tho centre one; thus proving ihat they wero not in a straight line, but dipping from the tangent.

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This experiment was reversed at each end, with the .••rime result. But the globular opponent's referee argues that as the two signals and cross hair appeared equidistant from each other in the telescope, for that leuon they roust be In a straight line from eod to end, and that the apparent dipping must be the result of perspective diminution; but those of us who know anything of the laws of perspective could inform him that nil objects standing upon a straight plane with their tops tho same height as the eye, must Hue with and cut each other, and that the bases only will vanish 'owarda a horizontal line passing through the eye. If the signals and cross hairs were equidistant, it wjuld prove curvature; to wit, if the CDd signal dipped (less refraction) 20tft., the centre one would dip 7ft. sin. By making a side view ou paper it will be lound to be a curve (horizontal scale, say lln. to a mile, vertical, Jin. to a foot).

The problem may also be tested perspectivcly by measuring the dips ou the vertical picture Hue. But as this curve docs not give the theoretical value—viz., rllit. in 3 miles and 20 57ft. iu 6 miles (refroctiou deducted), ns partly proved in first experiment, we have good reasons for doubting this equidistance. For the theoretical curvature tho centre and end signals should appoar twlco as far apart as the centre signal and cross hair-as may be tried by a perspective problem. In the diagrams of Mr. Wallace's referee they are showu about iu that proportion, but as all the diagrams seem to have been rough sketches, they must be taken approximately, otherwise a micrometer should have been used. A curvature has been proved, therefore, on Mr. Wallace's side, although doubted by thu opposite side. We may also consider it (Iu the absence of minute measurement) as the theoretical value, viz.:—

sighting 514 + refraction -8fl = eft. in 3 miles, sighting 20-57 + refraction 3-43 = 24ft. in 6 miles.

The diagram represents a geometrical side view of the combined experiment, with refraction lessening the actual dip.

K. 1". 1'uole, Grovetown, Weston-super-Mare.

FACTS WANTED.

Sir,—I confess to being somewhat sceptical about the astounding theory put forth by Mr. Henry W. Kevcley, of Heading (No. 280), respecting speed and power in locomotive vehicles, ft I understand his assertion rightly, lie states that the higher the rate of speed at which a vehicle is driven, the smaller will be the .-11111111 ur. of power required. If such a theory could be substantiated in practice, it would certainly be a Srand thing for wo poor velocipedists, who are keld down to something like eight miles an hour, by those mortal enemies to progression, gravity and friction. If tlie statement be true, that the higher the speed tho smaller tho power required, it follows that there is such a thing as a speed so high, that no power would be required at all. And having got thus far, might it not be possible to ceax our vehicle to put on a little additional speed, and so create a little surplus power to be applied to some praiseworthy object, such as grinding the coffee or churning the milk {vide Punch), while we were taking a short canter, (50 or M) miles) ou our veloclfere, before breakfast. I have read Mr. Keveleys epistle with much interest, and will become a convert to his doctrine when he brings one or two facts of vehicles of any description ever having been driven with less power at a high speed than a slow one. J. Hastings.

SCREW IN CHUCK-TO "HEATnEN JACK." Sir,—If you study "A. B.'s" drawing you will see that what you suppose to be a left hand screw Is a right hand female screw slioicn in section, and, therefore, has the lines representing the thread, slanting the same way as an outside male thread. As to the other point, you misquote my letier by leaving out the words '* of tho mandrel," alter "each end." I meant that the mandrei;is double ended, and carries a chuck on each cud;at tho same time, which necessitates one being screwed right hand aud tho other left. Lastly, it is by uo means uncommon to find right hand screws Inside the cylinders of back centres, and many prefer It, as it renders forolng up a drill easier work, owing to the workmen only having to lay hold of the fly wheel on the screw, anil keep pulling. So 1 don't think it wrong altogether. J. K. P.

JUMPING FKOM THE TRAIN.

Sin,—In reference to your correspondent's view on the subject of "Jumping from the Train," will you permit me to suggest what I think Is a somewhat difurentviewon this subject, but one that appears to me the correct one, and one that, 1 believe, has stood the test of experience with guards aud persons in a position to need the jump for safety when a train has been proceeding with great velocity. It Is to throw yourself with backward jump slightly inclining the contrary way to tho direction of the train. CI course nlwill easily bo seen that whou tho feet reach the •.round their motion will be arrested, but the rest of tlie body will fall violently in tho direction taken by tie train. If the jumper jump face forwards away from the engi e, he will come violently on the back of in i head; if h , jump be, as I state it should be, his tall Tviu be on h is face, but he will have bis hands

ready to break his fall. If his jump be with the train, forwards, he will add his own velocity to that of the train, which needs no addition. The ordinary idea is to jump forward in the train's direction; this will answer, and is the only way when the jump is from a carriage drawn by a horse ; but when the velocity is that of steam, ,10 or 40 miles an hour, the action must be different.

A very active little station master, well known to those who frequented Leicester station 12 or 14 years ago (Mr. Tyers) is, I believe, my authori'.y for this view, and it was more than onoe tested by his experience. I trust, however, neither I nor any of your readers may ever be in a position to require to try any method of leaving a train, but should ft be our lot, there appears to be more philosophy in this one than in any other. O. W. W. G.

SLOT CUTTING. Sir.—T enclose a couple of tools and Bample of work for " F. R.C.S.," which I shall be obliged by your letting him have on application. J. K. P.

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THE SALTAIRE-WARDOUR STREET LATHE.

Sir,—I am not quite able to make out "Natural Flat's" letterjp. 102, whether he asks for information in good faith, or to rile me by saying I state more than 1 can prove, or to defend the writer of the article which appeared with tlie drawing, or to make me commit myself to some further statement that cannot be borne out, with the notion that what I have already written is actionable somehow, only that I am not deep enough In tho mud yet. He is enough at home at Mr. Smith's and Mr. Salt's to be able to compare their two lathes, and to promise specimens from-it is not quite clear which. So he can't be at a loss for information.

I am sorry, as he is, that the description given was so meagre, and I am sure that the writer could not know much about the capabilities of the lathe, or ho would have felt real pleasure iu describing some of its novel features.

Now as to my statement—which I should havo been a bom fool to make if I did not know what the facts are. I said a " great part "was rejected. Nowlmin-ht defend the expression by saying that a purely ornamental lathe does not of necessity involve either bed standards, fly-wheel, crauk, treadle, or poppet-head', so long as there Is a maudrel with means of driving it either by hand or power, and a slide-rest; but this lathe is equal to a little more than marking crooked lines with peucil on paper, which is about as much as runny an expensive geometric chuck can do, and there • fore ic estimatiugthe " great part," we must take bed standards, Ac, into account. Now the lathe, when it camo from Yorkshire, consisted of—firstly, one bed fitted to; secondly and thtrdly, two standards; fourthly, one mandrel-head fitted with mandrel and pulley; fifthly, one poppet-head; sixthly, one flywheel fitted to; seventhly, one double-throw crauk. There was no treadle to It. The rejections were— firstly, one mandrel-head with mandrel and pulley fitted ; secondly, one fly-wheel fitted to; thirdly, one double-throw crank: these parts were remade. The leading screw, sad-Ile, and everything else except the poppet-head, which I have since heard was altered to correct the fault 1 pointed out, were mado by Mr. Evans. The saddle to carry the slide-rest was first

made to Mr. Smith's design, and had to be altered to make it act. The present fly-wheel is not the one which came up at first, though of the some pattern. I have already spoken of the overhead motion, and see no reason to alter my opinion.

As Mr. Evans's account amounted to some £1200. It is pretty clear either that the lathe was made by him, or else that he hod a very 4argu sum of munev paid him for not making IU J. K. p.

COMMERCE AND TRADE.

Sin.—Many fallacious ideas are based on such tigurcs as those quoted;by " Saul Rymeu," p. 101. Statistics are perfect edge tools, and want careful handling, wlille they can be made to do almost any thtug. It has been no uucommon thing for even statesmen to cry out because imports exceeded exports in value, toe sltoiMbeina bad way if then did not do so. The difference on the totals, if these could be really ascertained, which is a thing impossible, would represent the cost of carriage, or shipping, andourprofit. Would a man of business think himself well off if his sales, or exports, exceeded In value his returns, or importi>? Well, the same holds good of tho nation's commerce. Further, it is said, " But we have to pay tlie difference in gold"; be it so. la the gold wo receive or the bills of exchange, included in the imports 1 Australia sends us millions yearly in exchange for goods which count in the exports. Then it must be remembered, England is the banker of the world, her business accounts cannot bo balanced at one point, they include those of too many branch houses; her profits can only be ascertained in connection with the operations of the whole empire, nay, the world. Meanwhile, her material wealth is vastly accumulating, and being capitalized in the form of railroads, a commercial navy, such as no other nation, or all other nations together, cannot approach; in constantly Increasing loans to foreign nations; in works erected all over the world by her money, and bringing to her an annual return. Th ese lacts are much better evidence of the balance of profit of England's trade than any deductions from very impel feet and little-understood figures.

Sigma.

CHEMISTRY.

Sir,—Lately some articles on various points in chemistry, have appeared in your columns, doubtlessly as cleverly written as usual, although, as a rule, they arc more or less superficial; still, though they may be useful as showing their authors' views, they are seldom so for much else, being usually very elementary, are not necessarily the generally received views, and do not often exhibit more than one of the many sides to a question.

Those of your readers who wish for a thoroughlv reliable and scientific dissertation on tbe qnestion of "atoms," Ac, had better refer to the "Journal of the Chemical Society " for September, October, December. Ac. Despite the fine defence of the " atomlo theory." or rather of the single branch of it, it would appear to bo doomed as admitting of no proof at present, though it is probable, nay, very probable -. therefore we must regard as certain, that the branch of the atomic theory containing the assumption ot "Jtred material Indivisible atoms," will gradually be abandoned. Hut it must be remembered that tbe assumption of tho existence of these, we may term tbem, "materialistic atoms," as was well pointed out at the meetings of tho Chemical Society, "is not necessary to the Atomic Theory," and Dr. Williamson did not even attempt to prove the existence of them. No, the atomic theory is based on a much firmer foundation, that of "chemical equlvalentism," which has been so decisively proved by Stas to be correct.

Nature has a paper by Dr. Olding, on " Chemical Notation," an attempt to defend the system of symbolic equivalent notation on a basis apart from the theory 01 Walton's materialistic atoms, which he, along with many of our most distinguished chemists, abandons. Thougb it will fulfil its purpose, it is not a very good defence, though coining from Dr. Olding, of course correct. It is, however, unnecessary i\ the theory of definite equivalents, which has not been challenged, and on which his own defence rests, is of itself the best and most complete defence of our system of equivalent notation. Neither is the paper in Dr. Oldlng's usual brilliant aud concluslvo style, and Is not so forcible as would be expected from its distinguished author.

The views originated by Professors Wanklyn and Williamson, radically modified and nmended, it is true, are gradually spreading, and give hopo that tbe mist so' long persistently enveloping the questions of valency, radicalism, Ac, is at length being dispersed. They are. It is true, still in great confusion, und very rough, but this disorganisation Is due to the magnitude of the work, and they are gradually being brought i'lto better ondition. Undoubtedly It will prove a laborious task to reduce all to a proper system, and all parts may require great revision and amendmcut. When it is finished, and that I hope before long, we shall have the [questions of valency, di-, qtinuti-, nnd multi-valency ; radicalism, and di-rndicalism, polyatoinlcy, and poly-equlvalency, with the innumerable other analogous points, brought into an intelligiblo form; at present, it is some years1 work to even properly comprehend their meaning, much less to understand them.

Doubtless tbe "Harmonious Blacksmith" and "Sigma," hnve noticed the letter in Nature, of April 14th, on the dinnruls. Lately, there has becu two papers read before the Zoological Society on tbe same subject.

Oleic acid (Experiment No. 28171, is obtained by saponifying almond oil, decomposing the soap formed by an acid, and converting the fatty acids Into their lead salts by means r.f oxide of lead. Tho plumbic oleato is dissolved out by ether, aud decomposed by hydrochloric acid, the etherial solution decanted, and the ether distilled olf, leaving nearly pure oleic acid. It can be purified by converting it into its baryta salt; treat with alcohol, and decompose with sulphuric acid. Glycerine is obtained by saponifying any neutral fat, and is a secondary produce of the soap works. "Oculus" (No. 2608), will find that the Irritation of ths skin raiu-ed by sulphate of atropia, can generally b- preveuted by first adding ft little alcohol to U. M Ilrandau (five*, in his paper on chlorous acid, in the - Aunerleu dcr Chcmic oud Pharmacie. a uew method of preparing taric chlorate, which I find to be welly "ood. lie obtains the salt by digesting w-ell a mixture ol sulphuric acid, water, nlnminto sulphate, »ud potassic chiorate, tilssolves out with dilute alcohol \hv chloric acid, neutralises with baric hydrate, and then distilling ofT the alcohol. crystallises out the baric chlorate. It yields a salt containing 90 J per cent, of baric chlorate.

I note the letter oi Mr. Edward Richards. In your vaner on page 137, in which he fully details his uieiuod of obtaining the percentage of sulphur in iron by the nitrohydrochloric process. I do not conaider Ibe process itself the best, but the system of manipulation is very good, although for strict accuracy I prefer a few altera!ions in it, which I use when adopting it. though I generally use cither Ramuielsber-''s or Mitscherlich's method in preference For instance, the presence of a little chromic acid .lurinn- the oxidisation of the sulphur Is often an ■advantage, as effectually rendering the conversion of all the sulphur into sulphuric acid certain, and preventing auy fumes of sulphurous or chlorosulphuric acids, while it does not interfere with the after reactions Likewise, the neutralisation of any free acid mitrlc or hydrochloric) is advisable before precipitating the baric sulphate, as they greatly increase lis •solubility, so if it is not done, and the proportion of eulphurislarge.it is advisable to use the acetate instead of the chloride of barium. Even if it is done It -if as well to use the nitrate lu preference to the chloride of barium, as it is almost impossible to wash out all the chloridoby water alone, from the precipitate of

These precautions may appear trivial and unimTmriant, and perhaps, for reugh practical work, where only a certain degree of acouracy is needed, are so. For exact accuracy, such as is essential for reliable scientific work, though, they can not bu safely disregarded, as otherwise, as I have known, the sulphur may be considerably under-estimated. The effect their neglect may cause is seen if we remember that a small trace of nitric acid will raise the solubility of baric sulphate from 3 to 30 millegrammes a litre, while a little hydrochloric acid will more than double this ■ so much so, that sulphate of baryta precipitated by sulphuric acid from the chloride, will often have 10 per cent, held In solution by the hydrochloric acid ; indeed, I have known as much as 1*0 to 220 mlllcgrammoa per Tamme thus dissolved. Kirwan (" Ann. i hem. Phys."), and Calvert (" Phil. Mag.") well illustrate the raod of precaution in estimating sulphuric acid, through the solubility of baric sulphate In dilute- nitric and hydrochloric acids. Urban.

TESTS.

Sin,—1 am glad to inform " F.R.A.S." that my 3iu. refractor has separated Gamma Leonis, Epsllon Bootis. Delta Gemini; these are all the objects I have been able to try my telescope on, with the exception of Gamma Vlrginls. i)n turning my telescope on this star for the first lime, I found it double with my highest power (W times. Is this a favourable result? I should have tried more objects, bnt was prevented partly by light clouds and partly by the chimney-topi, widen form n great part of the scenery from our doorstep, lie will excuse my not sending better results, As when there has been a favourable evening I have been prevented from observation by engagements. J am much obliged for his replies to my queries in the English Mechanic of April 22. If "lingo" (2592) would place a piece of lime on the back of his small tairror it would keep It perfectly tree from moisture. This has been put into practice upon the plane of a ~k mirror, and gave satisfaction; but a better plan is to take the plane mirror out of the tube, aud to place it, silver face down," on a piece of leather well rubbed with rouge, W. Bagdxet.

JOE BARNES AND HIS YORKSHIRE SLAB.

Sin,—The other morning I called upon my friend, Joe Hames, and found him busy making a refracting telescope. Although remembering his success with a 131n. reflector, ground and polished by the most simple means, 1 was not prepared for what he had now to show inc. Having procured a squate piece ot Chance's camera flint-glass, he had set to work with four pieces of Yorkshire slab, rounded, ground, and polished his flint, addeil a piece of crown glass, and rouuded, ground, und polished that, usiug no iron tool, not even a correcting tool, nothing but his four slabs, and making a pitch tool for polishing upon them. Being anxious to ascertain the results obtained, ho had fitted the glasses intoasquare tube. This morning (Ap. 28) — the sun completely obscured by clouds—I could read the smallest typo in your "Correspondence column," at a measured distance of 100 yards. The diameter of the object glass is fliu., and its focal length about 7it. 3in., hut he says that the colour is yet under-corrected, and expects he shall have to make the combined focal length some few inches longer before the colour is properly corrected. As the construction of an achromatic telescope is always considered a matter of the greatest possible delicacy, and as meu of the greatest experience, aided by the best adapted meaus, sometimes find themselves disappointed in the results of their labours, 1 think the above shows that much may be done by very simple means, and that if so much oan be accomplished by a first attempt, we may expect ho will ultimately succeed in bid, to me, unheard of ejjeculatlon. If you think any of your readers would lie likely to Imitate Joe Barnes, they will certainly feel gratified in reading the above, and should ho ultimately succeed in making it to his mind, I will, on some future occasion, report. Progress.

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lathe, of which I forward a photograph. The uncovered wire Is wound on the large reel at the back of the lathe; from thence it passes over the small pulley attached to the lathe itself through the hoUow mandrel, which lias fixed to It the reel or reels of cotton for covering. As the wire is covered it is wound on the reel, which is supported by the rest socket The wire passes through the base of the wiading-on"apparatus, the reel of which has fixed to it a handle and click wheel. To the reel on which is ths uncovered wire, a small pulley is fixed at the outside, over which a cord passes with a weigh i attached to make It friction tight. This, then is the description of the machine. The other parts, shown In the photograph aro those of the rose engine. Of course the machine may be made self-acting by driving the windiug-ofl reel from the overhead motion.

N. 8. Heineken.

WIRE FOB ELECTRO-MAGNETIC APPARATUS.

Sir,—Some time since an inquiry was made in the English Mechanic for a descriotion of a machine lor covering wire for electro-magnetic apparatus. Ussy years ago I adopted such a machine to my own

REPLIES FROM " AN ADEPT."

Sip.,—Although still an Invalid. I must endeavour to reply to the various inquiries addressed to mc by sever nl correspondents. With rospoct to the query of G. M. Little, No. 2110, page 0'J. No. 263, a Bourdon is the most advantageous us a pedal orgao, but if the progress ;he has made in building his Instrument is not too far advanced, I should most earnestly recommend him to carry the principal, twelfth and fifteenth steps down to CO, or at all events to prepare the soundboard for their subsequent insertion, as I fear he has no Idea of the effect, of what he proposes to construct, will be, if carried out according to the description be has givon.

As your correspondent "Slddeley," on page 88, No. 264, asks my opinion upon bis proposal to place two feet to. one valved pipe, I consider he wouid fiud that the advantage would not compensate for the additional complication, and I presume that ho is aware that valved pipes in auy iorm aro not in favour In this country, on account of their great liability to derangement. Inequality of tone, and general inefficiency.

I bee to refer "Simplex," page 138, No. 206, to the commencement of my Instructions on page 67, No. 211, Vol. IX In the first three or four communications he will find, I trust, a pretty clear account of how to set out his soundboard, and also full details ol its construction which will include his other requirements, only. If 1 may suggest to him. tne substitution of a dulclana, in place of the trumpet, in his specification for the proposed Instrument, I think he will fiud it much more satisfactory.

In reply to W.J. Raybould, No. 2691, page 107, No. 267, the two artioles he has described and figured are "concussion bellowB," which are generally used in large organs, Blmply to counteract, the evil effects of clumsy or careless blowing. An Adept.

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TURNER'S PATENT STEAM ENGINE LUB1U Cator.—CARDING ENGINES.

Sir,—The description given by Messrs. Turner of their patent steam engine lubricator, p. 166, is not sufficient explicit.

What capacity is the cylinder? or how ofteu would it require filling during the day for a good-sized engine?

When the ram has driven out all the tallow at the bottom, what contrivance Is there for arresting Its downward motion, and so preventing It driving out also the bottom of the cylinder? If the engineer is expected to be at baud to throw It out of gear at this particular juncture several times during the day, and to wind up the ram aud refill the cylinder, I tear it would not get the attention it would require for lis efficient working.

Wherein conslstB the patent right ? as appliances of a nature similar to this have been In operation for some time, with the apparatus, so far as lean see, requiring less attention on the part of the engineer, and costing considerably less.

It Is difficult giving a satisfactory reply, without occupying too much ol your space, to questions which extend over so wide a field as that of "Excelsior's," (2648), on "the best cardingenglneat present in operation." Querists should state the class of work to which their questions apply as there Is a wide difference iu carding for Nos. 10s.. aud 100a.

Kor medium numbers I think of no better system of carding than with rollers aud clearors, properly set, and kept true, the stripping and griudlug being regularly attended to at proper Intervals. For liner work, breakers and finishers, breakers with rollers and clcarers, finisher engine with revolving flats aud self-stripping apparatus.

For the ordinary times of grinding I should prefer stickers to the pulley, one on cylinder and one on doffer, which aro also " worked from end to end of the engine by means of a spiral groove In the shaft," because at these tiroes all that is necessary to be done Is to brush the dirt out of the cards and to sharpen them up a little, which is donequicker with the sticker than the pulley.

When the emery rollers have been on for grinding true the cylinder and doffer, previous to sctliag. the pulley might be used for a short time to give better points to the card teeth. B. W. R.

SUNFLOWER.-RUSHES.—STARCH, &c.

Sir,—Having read with pleasure (p. 114, No. 205) an interesting note on the utility of the sunflower, I beg to add a few words to t. The seeds of the sunflower yield 15 to 16 per cent of oil. This oil is extracted in some parts of Italy and Germany; the refuse cake is employed as food for cattle. Samples of the oil. coming from Berlin, were exhibited last year at Amsterdam; the price quoted was, for the yellow. 15 thalers (45s.) per SOkil.; the white, 1»§. It is said that this oil, being very cheap, is employed in many cookiDg operations instead of butter or salad oil.

Several other seeds of plants of the Composite order have a good produce of oil, for Instance, niger seed, or Ram ll\\ IGuuoteaoleifera) yields 35 per cent.; safflower (Carthamus tinetorius), 10 per cent.; Madia sativa, 32 percent; Burdock {Arctium lappa) 19 per cent.

Another correspondent (p. 115) is quite right in considering rushes a good material lor paper making effectively. Some years ago, Chevalier ClausBeo, at one of the meetings of the British Association for the Advancement of Science, said :— " I found to my great satisfaction that the common rushes {'l^uncus efums, &o.), contain 40 per cent, of fibre, equal, if not superior, to the papyrus fibre, and a perfect substitute for rags In the manufacture of paper, and that a ton of rushes contains more fibre than two tons of flax straw." At Paris, in 1867, were exhibited seTeral samples ol paper made from Australian rushes, sent by Dr. F. Mullcr, Director of the Botanical Gardens at Melbourne; thoso rushes were principally Scirpus (Clubrush), Oipenta (Scdgo or GalUngale), Heleochans (Splkerusu), Aerofes (dry rush).

We. have had several very interesting articles on Starch; let me bring my "brick" also. A thousand pioneers arc wanted to discover all the useful substances which remain unemployed in far distant countries. 1 beg to give the names of some exoti

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STRBBTOTH OK CHAINS.

Sir.—Thanks for Mr. Laidlcr'ti llrst remark, which I duly appreciate. Theflrstformulareierredtooughttohajrc beeti given

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(1.) rf= s/6x 14 = -/ill! = »** = I"3125la- = 1-iu.

8 16

1 I presume thcro is a fault of the printer's in I — = d

IS

of his correction. Something similar appears lower down—namely, for the minus sign read =.

A-i to his second remark, I leave it entirely to those interested in the subject to multiply or divide by 30 or 3'2, but I will show that the results are so very nearly the same, that 3", and not 32, is the advisable number to take, as by so doing1 the calculation is much shortened, aud the application of the result not In the least impaired.

liis formula is:

211C6

d - s/ 32 x It = */ 41H = in. = l'3Z381n.

10

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I calculate to 4 decimals, as Mr. L. compelled me to do so in the first place. It will be seen from these two results that Mr. L.*s is by 00103 larger, aud mine by 00217 smaller, than the result In I, aud simply differ from each other by O'Ol, which, considering* the allowances made in the rule, need not be takeu Into account iinHi experiments lead to a more precise rule, and to which Mr. L. may apply his skill.

In table I. please to correct: 30, in which 14 tons = 302151b., aud read for latter 31001b.

A. Tolhausen, Waterloo-road, Manchester.

TIME.

Sin,—Your correspondent, "Not a F.R.A.S. " may be unhesitatingly told that the "Nautical Almanac" is right In the directions it gives in the pa;ro of tho "Explanations" referred to. "A Fellow of the Koyal Astronomical Society" has made the conversion according to those directions, and done so correctly (p. 86). But I must ask the last-named correspondent what he means by the paragraph which follows :—" I have assumed that my querist's longitude is Kin. 7s. In mean timo west of Greenwich. If it be 8m. 7s. sidereal time, he muBt convert this into mean time, which he will find to be 8m. 57s., and add that." This will lead to a wrong result, as "Not a F.R.A.S." has shown. The fact is, both your correspondents appear a little confused on the subject of tho expression of longitude in time. The longitude of a place 15° west of Greenwich is one hour, whether that hour be sidereal, moan solar, mean lunar, mean Jovian, or any other imaginable hour. If a sidereal chronometer and a mean time chronometer were brought from Greenwich to the place referred to by your correspondents, tho difference between the two times in tho two places would be 8ni. 7s. in each case. Tho conversion of sidereal time at any place into G. 3L T. is then a very simple affair. There are two methods. First, convert the sidereal time at the place of observation Into the mean time at that pla-:e, and then get at once the G. M. T. by adding the difference of mean time (or longitude,, which iu the case referred to is 8m. 7s. This Is the method followed by "A Fellow of tho Royal Astronomical Society.''

The other method is to go at once from tho sidereal time at the place of observation to the then sidereal timo at Greenwich, by adding tho differenco of sidereal time (or longitude), which is again 8m. 7s., and then find the G. M. T. Hk if on tho meridlau of Greenwich. This was Mr. Dawes's plan, as mentioned by "NotaF.K.A.S."(p. 135). It is evidently the better of the two, beiag rather shorter, and not requiring the introduction of the proportional part of 9-M&65.

I observe that Loomis heads ono of his tables *' To Convert Degrees into Sidereal Time." It would have l>een better to have omitted the word "sidereal." I have another table before mo, headed more generally: 'For Converting Longitude into Time." 11. P, D.

P.S.—I have unfortunately not soon your last number yet, in which there may be more on the subject, which would have rendered this unnecessary.

THE HARMONIUM.

Sin,—There are a few queries waiting to bo answered; some of them ought to have becu attended

to long ago, but the cold weather has been too much for me lately, and like '•Adept1'' I had to take to bed. Having got out again, I will with your permission get to business. And first in point of lime comes W. Holston who wishes to put a tremolo stop on one of Messrs. Matthews and Scott's patent swell box instruments, a very foolish wish to my thinking, butas that is no concern of mine, I shall tell him how the makers would .have done, *as I believe their 'system to be simpler and equally as good us the usual method. First, than, he will have to .cover the wind opening in the valve board with a leather-faced aud hinged valve in the usual way, carry action for opening and closing the valve out: through the back|of;the pan, connect It to a stop roil by means of the common sticker and flap, with the lever reversed so that when the slop is drawn out tho valve will be closed by its spring, then cut an openiugiiu tho valve board, 2lin. long. lin. wide, out of the line of large opening, so as not to weaken the board too much; cover this email opening on the upper aide wiih a piece of wood fnced with leather and hinged at one end like a common valve, takeu brass spring 10in. or 1 ".*ia. long, fasten it to the valve board so that tho free end of the spring reita on the free end of the valve. When you draw the stop already finished, and which Is labelled "Tremolo." you shut the largo valve the wind, in desporatinn, forces the wicket, the spring attempts to shut itajrain.and between the two ensues a battle for tho mastery; your business now Is to Rco that the soring is not too powerful for tho wind^; if it is, reduce its thickness with a file until the sound is to your taste. The end can be attained also by u-dng a piece of small wire fixed to the valve Itself, and carrying a small leu dan weight on its extreme end ; but I prefer the spring. There is one thini^mu^t be cirefully s^en to—vl/., that the large valve, when closed I* perfectly air-tight, any wind getting in there will infallibly neutralise all the work.

••VrVNo. '-\V», 'p. 530, 1730, will most likoly hare some difficulty in overcoming the defect in his instrument to which he alludes. The top notes of the treble are very often not nearly so well fitted as they might bo. and the consequence Is that the wind rushes through between the tongue and tho frame; moreover, it Is a very common fault to have the channels too large: and if Imui these faults come together, tho reed is choked with too much wind, and is utterly unable to speak a syllable. Another cause is the pallet holes being cut too large. The tir^t may bo cured by taking a chisel and hammer, lay the reed on some solid article, aud placing the edge of the chisel un the frame

of the 'reed about —th back from the tongue, tap ic

10 sharply on the top, thus forcing the metal forward on the tongue, a rub with a fine file will restore the frame to its original appearance. If the pallet holes are ton largo, cut a sheet of strong brown paper, with the holes a little less, and paste it over the original ones, taking enre that it is properly placed, so as to contract all the holes to an equal extent. Tho fact is, the construction of the harmonium is considerably to blame for this defect; there is too smull a space between the valve board and the bans reeds, ana a great deal too much sp;ieo at the opposite end; the space below ought to* bear a certain relation to the depth of channel above; now the reverse of this is what obtains, hence the common difficulty of the small roods not speaking promptly. The only cure 1 have ever tried with complete success was this: I cut the pan from the centre to the treble end on an angle, leaving it just the depth of the side Irons at the ends, then blocked up tho valve board to suit the? now (patent) pan, and the alteration on the music could bo felt, so completely did it change it. Now this is a somewhat troublesome and expensive alteration, but ichat wilt yanl If a musical! n«trumrut don't make music it ain't worth house room, and even alteriug to the exten/ Indicated, may in some ease* be more profitable than "new stock, lock, and barrel." The channels to bo right should bo something like the following: 4th C. 3th C. Top C Depth of Sft. .. \ .. h .. j

ion. ..j .. a ..

10 Length of 8ft ..21 .. \\ .. * 16ft. .. :;J .. 2j .. l

He can easily find out if that is anything like the size of his channels.

"E. J. B.," No.;237,'p. 589/1820.—Tho springs of the harmonium—I meau tho springs below tho reservoir, if unequally made, sometimes causes the music to sound in waves. The expression valve in some instruments is placed on the top! of the reserve boards, with ono spring attached to k?cp it open; in Bucii a case, if the valve is rather slim, and having a slight tendency to rise higher ou one corner than tho other, immediately you ceise blowing, the wind issuing from the reservoir Bhakcs the valve and thus produces the shaky sound complained of. It will, bo obvious that the same failing in a register valve would cutise tho same effect, but I have never mot with such a case. The first two mentioned causes being the only ones I have had to cure. In the matter of^curing the harshness of the reeds, I am afraid there is no other method available in the present case than the very effectual mode of treatment suggested by tho "Harmouious Mackamith" in the case of baby—viz., get it under tho blanket—smother it in short. Thus, if there is room between the ends of the pallets and tho inside of tho key frame, put a strip of wood along the whole length of the Instrument, glued t» the top of tho pan, and a trilie lower thau the key frame,*lt will be about 2It. Din. x £iu. x |}in.; get a piece of stout brow?, leather (colour no object), aft. 01n. x lAiu. or thereabouts, a piece of swausdown, same size, lightly glue the cloth to the rough side of the leather, mid when done, glue both on top of aforesaid strip of wood, thus" enclosing the pallets (and the sound) iu a jacket; this of course softens the flute as well as the elaxlonotte ; but us a rule, both aro the better of it. Again, if you have no fear of work, and any way handy, a first class method of'softcnlng the sound is to;iift the key frame np an inch clear of the pan. screw on pieces of wood along thebottonrt>f thekey frame.lin. thick, and allow them to project inwar^about^iu.,makeafrara'j, or rather a cover

similar to tlic'swcll.box cover, figured by,Mr. J. Matthews lately ; 4 openings in flt covered with shut'en, glue a sticker mil along top an-i bottom of it, drill 6i holes, cover under Ride with flannel or swansdown, place it inside key frame, resting all around on \\n. plinth, already specified, to which attach it with small screws. insert sticker*, adjust the keys, attach stop action to the shutters, and .you will have completely metamorphosed tho instrument; you will have music as soft as you can desire, or music "rank and strident," fit to ravish the ears of our dear ".Alexandras."

"A New Subscriber" (these long names waste ink). No. 2(», p. 661, 2107, requires ftft. reeils, and the pallet hole at lowest O will bo l^ln. x \\n., top Jin,

by —In., graduated between.

16

"Vibrator" (same page as last), asks If'any reader has met a trumpet stop on a harmonium. I have mst with titttop lahrt of that name on an harmonium, but •oihiug beyond that. The sound resembled a trumpet about as nearly as it, did a cross cut saw—had it been n good or even a fair imitation, I should havo " madea noteou't," hut as it was I didn't even look how it was do no.

W. II. Chorloy, No. 2T..S, p. tilrt, 107G. has precious little use for a tuning bellows. Ii hKroeda are screwed on the pan, he would be foolish to tako them off again for tuning. From his statement I am somewhat suspicious of the pan. Ilecda generally are uot in anything like the deplorable state he mentions, and beforohc begins to Hie the reeds, I would stroutrly adviseUiim to try another pan. if It is the first one he has made, ho will only be like his neighbour if it should not bo quite up to the mark. Neither do I see what good he N to do with a tuning bellows. If, as I t-uppose, he i* ouly an amateur making an Instrument for his own use, the, money spent ou a tuning bellows would be just [so much money wasted; the tuning bellows '* onlv of service where there are a great number of reed-; to tune. A stock of tuned reeils are kept there, and tho tuner place* one of these and one of the "raw," sido by side, and proceeds to make them both speak the butne. Hiving th'm «u a table beside him. he can do it more quickly, bat when put on the pan they have to be gone over again, so that W. H. C. will perceive the bellows would be of very little service to him. If after this explanation he N still anxious to make one. I will tell him how to do it; but I do not like to allow any person to go to expense without pointing out, as far as I can. what return they Rto likely to get for the money. The second part of his query he will have seen an answer for elsewhere.

"Valve," No. 265, p. 119, ^62, will havo to find out where he can purchase beech veneers \ of an inch thick aud Mn. broad. I cannot tell him where to find them, perhaps*"Tremolo *' will; I understand he was on the hunt lately; but with what success I d:> not know. Tho channels have no connection with each other; a two row pan is best made in two separate halves, and then fitted into the frames; the 16ft. channels being l\ deep at the bass end, and | at the treble (veneers included) the 8ft. channels lin. at basa end, and tho two veneers brought close together at the treble end.

I am making a set of drawings just now for an instrument after a different fashion than usual; but aa I, am fond of' proving before presenting, it will be soaie timo ere i can lay them before your readers. In the meautimo, will any of your correspondents who are on the "other form," tell me why a double manual instrument should be preferred Ma single, if the single set of keys can be made to do the work as well. For instance, why should H.J rows of roods got two rows of keys when ono rowtni^tit do tho work 1 Is it a piece of sham Invented for tho express purpose of still further harrassing the taxpayer's conscience—his tronser pockou ;"Th« Harmouious Blacksmith,' albeit a little "crotchety," being still a matter-of-fa3t gentleman wtth'a keen eye to superfluities wdl, perhaps, on tho above point kindly share his superior knowledge with Eleve.

CHLORATE OF RARIUil.

Sir,—Mr. Davis, as I write incognito, is perfectly at liberty to back his experience against miue, tJOij.h probably mine is ten times as great, and to decline to believe; It is very difficult to separate the c'dorate and chloride of barium by crystallisation, or, as in my former letter, " by direct means."

Though with no Intention of convincing Mr. Davie, naturally he will put his owu experience before that of others, I may remark that Chenevix (Phil. Trans.) declares it is not easy, us Mr. Divfs states, to separate the two salts. Jt is needless, a* tho correspondents my letter was addressed to can believe wh-> they wish to, or 1 might quote from the papers of MM. Millon and Surrulas (Ann. Ch. I*hys.), Waechter and Vaquelln (Schws. An. Ch.). or others, how they found It impracticable to do so by direct myitis, and had to employ phosphate of silver or other agents. Ramraelsberg, though, goes farther, aud denies its practicability, owing lo tho persistant retention of ascertain percentage of tho chloride. I quote the above solely to show my as-ertion d-ws not alone r^st on my own experience, and not wilh any intention of arguing; tlint I decline pending an answer to, and explanation, of, tho circumstance compelling my letter of Sept. 10, 1800.

MM. Regnault and Dumas were, quite content to> accept Chenevix, and Surrula*, and Rimmelsberg; results on faith; aud so was I, even had my owu results not fully borne them out.

By repeated crystallisation the per centage of chloride can bo reduced to a small percentage, bnc not to absolute pur.ty. It is perhaps unnecessary to remark that my letter of the Nth uU. referred solely to the salt that, would he produced by hK method ':ontalued In his letter of March 25th, which directs bat one crystallisation.

Concerning hypochloric acid, its existence is acknowledged by a number ot continental chemists, while that of chlorous acid is by most, including Dumas, Gmolln, Regnault. Uaxnmelsberg, i<nd Wanklyn.

Finally, it is quite possible for a very large number of facts to be unknown to young chemists that are not necessarily so to those who for years have had al)

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Sir,—lu your issue of April 15th, I have rend with fa to tot a letter by Mr. G, E. Davis on "Quantitative Analysis.'* especially that part referring to " estimation of organic nitro^eu and carbon." The process there trivou is that known as " Frankland and ArmBtroDij'*." There is also another method known as Wnnslyn, Chapman and Smith's, in which the determinations are made iu a totally different manner, excepting perhaps ammonia by Nesaler test.

in estimating quantitatively the organic matters fa water by this mode, Wanklyn tirst determines the ammonia ami urea, and secondly the ammoula derived from decomposition of albuminous substances, and from the relative quantities of each he pronounces the gooduess or badness of potable water. This decomposition Is effected through the agency of ao alkaline solution of potassum permanganate. Of course each inventor claims the superiority of bis own discovery over those of others, and I believe that Cbapmau goes ao far as to say of FrankInnd'a process—I write from memory—that the maximum error is greater than the actual amount of organic nitrogen present!

On the otht-r hand, Fraoklaml assumes to show that »he permanganate process of Wanklyn is not reliable.

fl owever, 1 understand that this latter discovery lu analysis baa been adopted by some chemista, notably by Dr. Angus Smith, in determiuiug- the organic nitrogen In air. What I am desirous of obtaining is the candid and Tunbiussed opinion of your correspondent Mr. G. E. Davis—as well as of others— of the relative capability of these two processes which will give the most accurate results, upon which i- the most reliance to be placed, in both cases paying due regard t*# the time consumed, and easiness of manipuhition, together with any other easentail conditions?

Frauklaud writes that there is no known meausof determining accurately the actual amount of organic matter In water, but some general idea may be gathered from tho quantitit-s uf organic carbon and organic nitrogen present. It will be observed in bis reportsof w ater analysts that the organic carbon and •organic nitrogen do not bear any relative proportion to each other in different waters; by way 6f example, the ratio of carbon to nitrogen in A water will be % to 1, in 14 water 5 to 1, inC water 10 to 1, and so on- No doubt this difference in ratio is due to the character of the organic matter, whether of vegetable or animal origin. Now what I am desirous of knowing Is, are there any means, and what are they, of approximately compaiingtheorgauicjoarboaand nitrogen of Frankland with the old mode of "organic matter" as expressed in grains per gallon? I-am aware It would be necessary in tho first place to consider whether the organic matter was a vegetable, animal, or, very possibly, mixed character, and a good idea would be gleaned from the proportion of each constituent pre&enf, snfncieutlyBO to approximate to the quantity of organic matter.

This would avoid nil necessity of evaporating a known bulk of the water aud incinerating the residue, when It is desirable to compare with an auaJyais under the old process.

There are a few queries I have to put, and to which I shall be pleased in having the opinions of youi correspondents.

1st. Are both Kranklnnd's and Wauklyn's courses of analysis suitable for waters containing large quantities of organic matter—for example, sewage-and would the processes differ from those applied to ordinary water I

2nd. Can the Ncssler test be applied to the determination of ammonia in ammoniacal salts—with previous distillation if required—and as accurately as by triturati g with standard acid?

3rd. Is it practicable to determine the quantity of nitrogen present in manures by Eraukland's, and particularly by Wanklyifs process, for wato r analayfs.estirnatiDg, in the latter case, the resulting ammonia by Neealer, or trltu&tiou?

4th. What is intended to bo understood by "one 'legrte of onrnufe matt er," as stated by Mr. G. K. Davis, page 603, Vol. X. W. K.

THE ESGLISH MECHANIC, ENGLISH MECHANIC MUTUAL IMPROVEMENT SOCIETY, Ac.

Sir,—No doubt you have recently had numerous testimonies and congratulations relating to the improvement effected In what may bo called, par excetlence, " our " Journal. From what I hear in Plymouth and neighbourhood, the number of your subscribers a^.d readers has been very much iucreascd. When itbecame known that Mr. Pasa-nore Edwards liae became the proprietor, if not the Editor, of tho KsfiLisu Mechanic Andmirkohpf Science, many (and I amongst the number) became subscribers. Wo had not forgotten how manfully he contested Truro at the last general election. It was, takeu altogether, • notable straggle, forthougu he fought almost singlehanded against old prejudices wealth and territorial influence, most people felt certain he would have been returned, so strong was the current of popular feeling in his favour. Km, like many other able men, he was defeated. Possibly his defeat was not altogether a matter of regret, as what the House of Commons may bare los», the English Mechanic may have gained.

If such Improvement can be made in one journal in a few months, what may we not expect by-and-bye, and

farticular]}- as new mutual instruction societies are Ikely to spring up through its instrumentality! It is About thcte societies that I should tike to say a word.

It occurred tome that wo tnigh establish one in Plymouth; but I found on inquiry that the subscribers here belonged to members of all classes of society, aud that, apart of being subscribers to our journal, there was not much community of feeling between them. One gentleman 1 found took it in for its astronomical information, another subscriber for its microscopical information, though he complained that miscruscopical matters had such sparse consideration in its pages; another for Us chemical inlormation, and so on. What rather surprised me was the large number ol what I may call well-to-do people, who subscribed, in comparison to those who may be termed workmen. As far as I could ascertain, the English Mechanic Is not so much read by intelligent mechanics as by amateurs, and scientilically inclined middle-cla*s people. I am in one respect sorry it Is called the English Mechanic, I wish it had a more geueral name such as tho Scientific Journal, or something of that kind. However. I suppose it Is too late now to alter the title. As our readers aud subscribers are in so many respects so dissimilar in taste and occupation, I think it would bo vcry difficult to form out of them a new society, and such I fcaf will be toe case In Edinburgh, Manchester, Ulackburn and other places. I don't say this to discourage our friends elsewhere, but to induce them to look at allihc facts; for I should not like to hear of them making unavailing efforts to form new societies, much as they may like to promote a friendly let-ling aud mutually instruct each other in the attainment of useful knowledge. Whatever may be the result of the experiments made, we are all in one sense members, as, 81 r, you have said, of a national mutual improvement society. It matters not what we are, or where wo live; we may be millers, or cottonspinuers, or electricians, or workmen, or students, we can all be teachers aud learners; we can all ask and answer questions; we can all deposit our mites in the treasury ; or, as you have put it, bring our bricks to the Temple of Knowledge. W. U. J., Plymouth,

EXTRACTS FROM CORRESPONDENCE.

MB. BKARDSLET'S LETTERS.—Mr. Dyer says: —" Iu printing my note respecting Mr. BeardBley's letters, you have, omitted the name of Mr. Carpenter, thereby making tuo say that "Mr. Beardslcy is an ardent advocate of the views of 'Parallax,' and has written a book entitled ' Theoretical Astronomy Examined aud Exposed,'" &c. What I said was: "It does not appear to be generally known who Mr. Carpenter is, the referee of Mr. Hampden. He is an ardent advocate of tho views of ' Parallax,'," &a

BLUE MAIIOK WOOD.— For tho information of "The llarinouious Blacksmith," MessrB. Muudy, Harley * Co., of lio. Bunhill-row, state that they imported a little parcel of the wood about two months ago. Mr. C. Nutting, of Digbeth, Birmingham, and Mr. Ogden, of Wiucbcoinbe-street, Cheltenham, supply fishing-rods made of blue mahoe. Messrs. M.ll. & Co. believe thatgrcenhcart stands well for fishing-rods next to blue muliou wood.

PLAN EOll CUTTER-BAR.—William II. Stone writes:—"As you were good enough, some time ago,

[graphic]

to engrave a plan for a Bimplc cutter-bar which I sent you, perhaps tho enclosed modification of it for the tool-post of a screw-cutting lathe may not be without value. I use it specially for holding the new tools of 'Musliet a special tool-steel.' which, if set at the proper angle, arc remarkable for the amount of work thev will do."'

THE " PHANTOM " WHEEL.-G. Sykcs. of IludderBlield, says :—" Seeing some correspondence in the English Mechanic respecting tho 'Phantom' wheel, I beg to state that I am at present using a pair with india-rubber tires, and I never saw anything to surpass them. They are light, strong, aud very easy to drive. The rubier tires do away with all the rattlo and noise, and are a very great help in uphill work, as tbey do not slip like the iron tires. They are equally as strong, if not stronger, than the wood wheels, and not much more than half the weight. I do not find the Bpringluess about the front wheel lhat Mr. Tydeman objects to so strongly, and think it would have been better if he had tried the wheels before condemning them. I have given them a good trial, and fiud them to be all that the 'Phantom' Company say of them."

UTILISATION OF WASTE MATERIAL,—A new

utilisation of waste material is reported, from the Briudisi district, iu the oil trade. Formerly the olive husks, as left by the common oil presses of the country, were used by the peasantry only for fuel, but a French speculator is now buying them, at tho price of 20f. per ton, aud shipping them to Marseilles; where, after undergoing some chemical process, they are put iuto a steam ptees aud made to yield SO percent of oil. The Brindisi people are themselves erecting a press, capable ol operating upon 70 tons of husks per em.

REPLIES TO QUERIES.

r2288.] -ADDRESSES WANTED. — I have received four or live addresses for "foreign correspondent." Direct letters. Including port-flump for reply, to J. D., Post-office, Melle, near Ghent, Belgium. —J. D.

[2450]—OLD COINS.—If the querist had read the note, reply to Quory 1243, he would have seen easily that it is a Nuremberg counter; that note givin" all the principal characters (H.KRAYWINKEL, NUK. R.PF. iVc.i.; yet several persons mode similar queries. Had they observed those characters they would have spared the Editor the trouble of engraving their quite worthless coins.—K. L. M.

[24!>6.]-PIIOTOGRAPHY.—lam sorry that I did not answer this query before, but engagements prevented. A clear glass may bo attributed to mauy causes. 1. The collodion may bo insensitive; In that case the same exposure as for sensitive collodion would not do. 2. There may be too much acid in the developer to allow it to work. 3. The bath may be very much loo weak to allow of a deposit. 4. There may be under-exposure. Now I suspect that the last mentioned iB the real cause. Of course I am taking a view of the case literally—i. c, a clear (transparent) plate. In tho case of a plate having no image, the causes are exucily opposite to those I have mentioned, but then the plate must be fogged, and would be only semi-transparent. If thorough utteutlon to the formula; advlsedby me some timo ago in tho English Mechanic fails of success, why I do not think that 1 cau suggest where the weak point is. If tho querist will write a fuller description of his plate I will try aud help him further.—Mus.

|23uS.]- FASTENING STENCIL COLOURS ON PAPER.—To fasten steucll on paper, mix the colours with dissolved gum.—J. F.

[252S.1-MUSICAL BOX.-Harry Bertram, p. lBi.iu his reply, repeats his lesson very well as far as he has learnt it, but makes a mess of the " Geneva stop " and its action as regards, at least, its efl'ecton altering the tunes, with which tho stop has nothing to do at all. —J. K. P.

[2536.]—OLD COIN—Perhaps " Bernardiu" will excuse my saying that this coin was struck in and not for Dallkarlcn, but for circulation In the whole of the kingdom of Sweden.—D. T. Battv.

[2537.]—WRITING TELEGRAPH —The mannal "liandbuch der Elektriscbon und Telcgraphen," by T. Forsach, Vienna, 1834, dscrlbes the plan of an "American" writing telegraph, of which the two principal partB are two cylinders having an helicoldal isochronlcal motion, but tho name of Meyer is not mentioned In the extract I have seen.—Bernardin.

[2340.]— SMOKE ON WALLS. —Where walls or ceilings are cracked, air will pass In or out, according to circumstances. In the ease of an ordinary room, having a lire, the air will enter by any or every means to replace the ascending column In the chimney; where rooms are shut In closely these cracks form the readiest means of admission. Besides the column of air in the chimney passing outwards, there is an upward current (n the room immediately In front of the fire, caused by Its rarefaction by the fire. This current, on reaching the celling, takes a spreading course towards the extremities of tho room, the small currents or tributaries take the same course, and prevent any deposit within the area of their immediate influence, while they somewhat retard the force of the main current immediately behind them, and so allow of a greater deposit; so it will be seen that the edge nearest the fire shows a sharp dark line, the opposite being white, gradually softening iuto the general tone of the coiliug. — Hakvev Saunders.

'jam.] — GILDING BATTERY.—"One in a Fog "has seemingly made a great mistake, He thiuks that It Is all done lu a hurry; let him uBe ouly one Danioll'8 cell, and use sulphuric acid diluted with at least .3 or 4 times its bulk of water. Fill the copper cell with a saturated solution of sulphato of copper, and only put some spare crystals to keep it concentrated on the outsido rim. His great mistake seems to be that he expects gold to be laid before there is any In the solution of cyanide of potassium. On the positive pole put a piece of gold (beaten or rolled out so as to uxpose as much surface as tho piece to be plated), and then on the negative pole put firstly a piece of plalioa foil until the solution is oharged, which cau be told by gold appearing on the platinum. Then, and not till then, remove tho platiuum, aud immerse the medal, coin, or whatever it is. If 1 have timo I will send a letter to tho Editor next week, containing a few hints which may be useful to him if he means doing the thing practically. Do not have the bath heated above 13v or 20° Reuumur, nor have too great battery power, if you do not wish to waste gold, as it will lay itself in a brown powder if the current be too strong ; in fact, with weak currents about l-30lh of tho gold is set in powder if you wish to Bet it auy thickness. Carefully weigh your piece, and then you cnu easily know how much you have laid. As soon as tho surface begins to grow dull it would be advisable to take it out and clean it with a stiff brush. This will not be required so frequently if you keep puttiug from time to time fresh pieces of cyanide of potassium in the bath. Abovo all things do not be in a hurry and forget to have your article to be gilded quite clean, and of all thingB free from mercury, which is very liable to get on the hands in putting tho battery together, for the smallest panicle will spoil tho gliding.—Tangent.

[•25470-I'RINTlNG NAMES ON PLANS.-Fig. 1 is a tracing of a set square that I made some timo siucefor ruling the slanting strokes of Roman capitals

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