with square hole through same, one end of socke. is 1 in hole at end by, and in middle 1 by it This long way-hole at one end is made to admit a wedge D to tighten end of boring bar B: when put in wrought-iron bar B has a nib turned at end one side, so as to pass out of hole, which is made in straight side of socket opposite the wedge D, when

C

the bar B is put in the hole, and nib put out of side hole, and wedge D drove in it keeps rod firm, and cannot come out. A is the end of other rod, it is put in the square hole end half-way in, and hole drilled through socket and bar to admit pin to keep in its place. This end never needs taking off. When the rods want uncoupling, drive out wedge D, and put out bar B. The hole in socket can be made any size for rods. Metal in socket in. thick, and light band of wrought iron round end to keep socket from bursting. I have made them, as above, to bore a hole 100ft. deep.-ALBERT HALL.

[34882.]-Air Compressor Pump.-The machine "A Working Engineer" describes seems rather a complicated affair. Transmuting 50lb. steam pressure into 50lb. air, without loss by friction, in no given time, one might suppose was a something invented to puzzle some relative of Beelzebub with. For instance, had it been put 15lb. to 3,000lb. in fourteen hours, one might have supposed some reference was intended to the secret concealed under the Chinese lock, which, when at last picked, disclosed a gigantic hydraulic machine for cracking nuts. This A. W. E." cannot mean, because no mention is made of time. The difficulty lies in understanding how a steam-engine could be supposed to throw anything through its air-pump into a receiver at 50lb. pressure, till at least the air in

the receiver itself is at about 50lb.-W. P. T.

a

[34917.1-Preparation of Ozone.-There are variety of ways to prepare ozone, the chief being those in which electric sparks are passed through a jar containing oxygen or air (the whole of the gaswater being transformed). On this footing many apparatus have been constructed for generating ozone (0,0=48). One of the cheapest and simplest is the tube ozoniseur" of M. Houzeau. It consists of a glass tube analogous to those used in the collection of gases, in the interior of which is placed a copper, lead, or platinum wire from 15 to

233 inches long, one of the extremities of which the superior part of the tube. This orifice is hermakes its exit through a lateral orifice arranged at metically sealed by means of a blowpipe. On the external surface of this tube another wire of the same metal, and of the same length, is rolled so as to follow the direction of the wire within. These two wires are placed in communication with the poles of a Ruhmkorff's coil, giving sparks of about fin. in length, the result being that a powerful ozonisation of the gas takes place. If ozone is required in a larger quantity, Siemens's ozone-tube should be used. It consists of a glass cyclinder, about the size of an ordinary test-tube, lined on the inside with tin-foil, which is inclosed and fixed in an outer tube coated externally with the same material (see Fig. 1). The extremities of the

Now to convert the passing gas into ozone, all that crown obtained, having a higher refractive and is necessary is to send electric sparks through the lower dispersive power than heretofore; but to chamber. This is done by attaching the platinum meet prejudices or doubts, object-glasses by the wires, which are connected with the tin-foil coat- same makers are at present also being made of the ings, to the poles of a large induction-coil. The usual construction, combining two flint concaves, complete arrangement shown in Fig. 2. Refer- in order to give the privilege of comparison. Not ences: A, battery; B, induction-coil; C, ozone much importance can be attached to criticisms made generator; D, chamber for reception of ozone; E, without responsibility under initials, as queries may gas-holder for reserved ozone; G, pump for ex-be suggested, and replies prompted, from motives of tracting air.-E. K. DIXON. interest or partisanship. In England and on the Continent there are now numbers of makers who turn out excellent object-glasses, and rivalry amongst them induces perfection. The trade is a garret one, in which any mechanic with a few pounds to spare, and commanding the requisite knowledge and skill, can enter upon at once, but without much prospect of ever growing rich at the work.-F. H. WENHAM.

[34932.]-Gas-fitting Cement. In page 401, a cement is recommended for gas-fitting. Will someome say what proportions of resin, beeswax, and venetian red should be used in making it? JOHN

KING.

[35093.] Ross Patent Objectives.-Allow me to thank E. D. W." for his reply (ENGLISH MECHANIC, Jan. 3rd). The ambiguous and obscurely worded paragraph, from the official report of the Philadelphia Exhibition, really teaches us nothing, as it deals more with principles of construction than with actual work, which is the real test of quality in an objective. It would apply equally well to the new formula glasses of both Ross and Powell and Lealand, as both are said to be made with single fronts. Has not "E. D. W." mistaken the price of his in.? The lowest price in Swift's catalogue is 35s. for one of sixty degrees angle. This is rather more than 1-5th part of £7 7s. Od., the price of the Ross 1-7th. I have not yet seen any of Powell & Lealand's new formula objectives, but, as I have caused the publication of "E. D. W.'s" somewhat unfavourable report, which may do Messrs. Ross & Co. harm, I must in justice to them say, that since I sent the query for insertion I have had an opportunity of trying a 1-5th of their most recent make. This has a new cover adjustment, by which the whole adjustment from uncovered to wet is accomplished by one fourth of a revolution of the collar, which is a great convenience in use. This objective worked well through some depth of water in a live box, displayed the proboscis, antennæ, trachea, legs, and feet of an Empis in balsam beautifully. The usual diatom tests, P. formosum and angulatum, were shown in a manner that left nothing to be desired, and the sharpness and clearness with which both sets of lines in a coarse rhomboides in balsam were shown was admirable. It will be seen that nothing very difficult was tried, yet I think more ought not to be required of a good working 1-5th. Three other objectives of similar power and angle were tried at the same time, but the new formula 1-5th was certainly the most brilliant and clear.-BETA.

[35289.]-White Glaze.-The glazes used in the potteries vary to a certain extent according to the ideas of the workers; but there are three kindsthe common glaze, the printing glaze (to receive impressions), and a slightly different kind for use on pottery that is to be ornamented by hand-painting. Common clear glaze is made of 53 parts of whitelead, 16 of Cornish stone, 36 of ground flints, and 4 of flint glass ground with water into a cream or thin paste. The proportions are, however, frequently varied.-S. T. K.

[35298.]-Darkening Walnut.-Slaked lime, one to four of water, will do for some kinds of walnut, a weak solution of sulphate of iron for others; and yet again for other kinds a weak solution of pearlash. Try each on the wood, and choose the one you like best.-S. N.

of crack, just where the sound metal is, drill a small [35300.]-Cracked Church Bells.-At the end hole, then saw through the crack so that the edges are clearly apart.-THOMAS, Loughborough.

[35303.]-Making Harmonium.-Reeds are voiced by bending the tongues. Impossible to give directions: a few attempts would teach more than volumes of writing. If "Basson" persists, I will send him sizes of the reeds, but it is simply waste of time for anyone to make reeds for himself. The swell simply incloses the pallets and the action, below keys; the fortes would open the swell shutters. The grand-jeu is merely a rod extending the length of the back which has projections pressing on the flaps of the stop action, thus opening all that are required with a quarter-turn of rod; a good manual coupler was illustrated on p. 443, Vol. XXIII.-HENRI ETIENNE.

[35309.]-Chemicals.-Drills.-Am I right in

supposing that when you dip a red-hot drill into heat quickly.-B. P. A. mercury it is made hard because suddenly cooled by the mercury [a good conductor] abstracting the

[35310.]-Telephone Wire.-Ordinary Telegraph wire gives as good results as any.-T. M. R. the only cause that can be assigned without looking [35323.]-Harmonium.-Bad construction is for oneself. When do the reeds whistle and squeak?

-HENRI ETIENNE.

[35332.]-Colouring Pipeclay. - What does "Valet" want to colour the pipeclay for? Fuller's earth or benzole will remove the grease, and any of the colours mentioned may be used if necessary.— J. M. B.

[35342.-Rule Wanted. What "A Country Amateur" asks for has been given several times. He should refer to his indices.-OLD SUB.

[35093.]-Ross's Patent Lenses.-These cannot be fairly condemned upon a comparison of the recent ones. In these and other object-glasses by performance of those made some time back with different makers a great advance in definition has lately been achieved. In high powers the results obtained by the duplex front leave no doubt of its superiority. It is an established fact in the optics of the microscope object-glass that one negative or concave of flint-glass may correct any number of convex lenses of crown glass, simply because if the foci and proper distances between them are judiciously arranged, additional lenses, so far from correspondingly increasing the chromatic and spherical aberrations, actually diminish errors arising from this cause. For example, if an achromatic consisting of a concave lens of flint-glass between two convex lenses of crown be made with a large diameter and deep curvature, for the sake of obtaining aperture, it will fail in this respect, as the aberrations will be enormous. A stop must therefore be employed to cut off the marginal rays [35344.]-Conversion of Motion.-If "Queand confine the defining ones to a small angular rist" wants a rotary motion, on the same spindle pencil in the centre. Now, if we take off the crown that reciprocates, his connection for reciprocating fenses and substitute each of them by two others shows it impossible. (Can this be done without having collectively the same refraction and magni-strap or gear?) There is a possibility, I have no fying power, it will be found that this sub-division doubt, but it would be of no utility when done. If surprising degree the chromatic and spherical aberra- purpose? Thanks to "J.C." and "A. T." for into four crown lenses will have diminished in a very noise is an objection, would friction gear suit his tions. This last will then appear as over-correction, reference and explanation.-T. WESTWOOD. and in order to eliminate this colour the radii of the concave flint must be made longer. Thus one flint lens will correct the errors of four lenses of crownglass more easily than it does of two only, with the advantage of large aperture. In the most recent and perfect object-glasses of different makers having theduplex front," this principle is in reality A far more complete description of Count Rumford's [35346.]-Smoky Chimney.-To "POND."embodied, for in them we have two concaves of flint correcting without difficulty an arrangement of five convex lenses of crown-glass including the double front. One flint concave is also capable of performing the same duty. This arrangement requires great nicety of collar adjustment for cover thickness or the "immersion" fluid. This with some is no doubt an objection. On some future occasion I intend to illustrate a theory on this question: it is one on which at present I am reluctant to speak, as by some interested motives are imputed to me for so doing; but I cannot even tell the prices without referring to a catalogue, and am not accountable for their cost. The first difficulty of obtaining suitable glass has now been removed, and a fine quality of hard

[35346.]-Smoky Chimney.-"Pond" will find what he wants in Count Rumford's "Essays." Will send an extract if desired. This subject has been well ventilated in the ENGLISH MECHANIC.D. N. E.

Fireplaces than probably space enough could be afforded for here, is to be found in his "Essays," 3 vols., printed about 1802, and lately re-edited by a Boston Literary Society in a very handsome style. Latter edition is to be found both in the Patent Office Library, Chancery-lane, London, and also in the British Museum Library. I can strongly recommend Edward's work on Our Domestic Fireplaces" as a most interesting and useful work by one who has very carefully and thoroughly almost every other source of information, I should studied the subject, alike in above essays and imagine.-F. W. S.

[35347.]-Werdermann's Electric Lamp."Pond" has forgotten that the electrical resistance

of the lamp has nothing to do with the total resistance of the machine. I am thinking it would require a very heavy weight to run any machine capable of producing the current for an electric lamp.-MINOS.

[35356.1-Resonance. To reinforce a sound can only be done by adding another soundboard or instrument. I hold that it is impossible to force more sound out of a soundboard than there is in it. Every substance has a sound more or less, and it can be induced but not reinforced. To say that a tuning-fork or set of strings reinforce the sound of a soundboard is as much as to say that the drum-sticks reinforce the sound of a drum. No; they elicit the sound by means of vibrations. We may play loud or soft, and alter the quality or timbre, but the total amount of sound is the same normally, only called forth differently. A soundboard or tube have no vibrations of their own, therefore they cannot have converted vibrations. Will Mr. Field explain why two strings tuned in unison on a violin do not sound louder, or why a tube held over violin or piano strings has no resonant result? If the tube reinforces the sound there ought to be an addition. It is not the column of air that causes the sound, but the vibrations that fit the size of mouth or edge; and indeed it is not necessary to use a tuning-fork, for, by blowing across the edge of tube or bottle, a much better sound results. No doubt air as a substance is more capable of resonance than any other sounding body; so, although the tube of glass or brass, &c., has so little sound in itself, yet the edge has sufficient resistance to set the vibrations in action on the air, or move the centre of sound to produce perhaps the largest amount of sound. Air is therefore a soundboard or body, as well as the medium of sound. Vibrations act on the air as they do on a board, and form their particular figure according to the force used or the manner by which its quality is determined. So to produce the loudest tone it is always necessary to act as much as possible on Nature's universal soundboard-THE AIR. I think this is important to know, because most persons believe that it is the air causes the sound, whereas it is the vibrations; and it is a common thing to illustrate a lecture on acoustics with diagrams of wave lines and ventral segments, which I am bold to declare is a mistake, for they illustrate only the motions of the substance or string, and not the vibrations of sound. Their illustrations I hold to be optical delusions; for, take the instance of a vibrating string, and if you will only think that, as the string is stretched very tight, it is impossible for it to double over itself and produce the figure 8-in fact, can it be done with a loose string fixed at each end? But then the theory is that the more tension the more doubling over takes place. The nodes are the centres of sound, so, as Mr. Field says, the tube by lengthening will respond to one tone without a bottom, and I think he infers a half would do as well, or a quarter, for one tone, because it has only one centre; but a soundboard has many centres, and the air most centres. The wind whistling through a key-hole has no tube-how are the nodes obtained?FIDDLER.

[35414.]-Air in Water Mains.-I notice on page 569 Horner" recommends fire-plugs, viz., those with indiarubber balls as being the right thing for getting quit of air in high levels. The statement is quite misleading, and I am only induced to write on the subject through fear that some one whose head is not on the right way might possibly accept the suggestion he offers. The valve abovenamed is not self-acting, neither was it ever intended to be so. The ball is held up in its seating by the pressure beneath it, it matters not if that pressure is air or water. There are, however, self-acting devices by means of which air accumulations can be and are removed. I inclose a rough sketch of

-A

B

one form of these air chambers, which nearly explains itself. A, road level; B, valve; C, airspace; D, float; EE, water-pipes.-CARNFORTH. [35423.]-Indiarubber Joint.-A piece of paper same shape as indiarubber will free the rubber from plate. Why use rubber for this purpose at all? Tukk's Patent Packing or other packing of a similar description 5-8th diameter will last long,

and at less than half the price of indiarubber, and there is no trouble in opening this kind of joint.PAPERMAKER'S ENGINEER.

I

[35430.]-Legal.-This query raised no question of "justification " of C.'s conduct. The fact is that he had nothing to sell. The property, in the eye of the law, belonged to B., and if B. died it would pass to B.'s heir or to the person to whom by his will he left property belonging to him as trustee, and the heir of the original testator had no more power to sell it or transfer it than any stranger. As the matter stands now, the purchaser is a mere trespasser on the property. Hence it is clear that the matters referred to by "H. C." in his further letter do not affect the question. I have only this further to add: It is "B.'s" clear duty to take steps for recovering the land for the benefit of those for whom he was made a trustee under the will of the original testator. In saying what I have avoid any speculation as to who these persons may be, and, of course, if "C." is one of them, it may considerably alter the aspect of the case, and, of course, B. would be free from all responsibility in the matter if all the persons for whom he was trustee released him by deed from all claims in respect of it. In this case all that would be required as to the property would be that he should execute a deed in which the facts were stated, and by which he conveyed the property to the purchaser. And now, I must add the universal advice in such cases, that "B." should, before he takes any step in the matter, consult a respectable solicitor. SPERANS, Lincoln'sinn. [35434.]—Angle of 70°.-If H. J. Hillenne will allow me, I should like to add a note upon his elegant solution of this question. "Novice" and others must remember that there is a difference between a construction which is mathematically correct and one that is sufficient for all practical purposes. There are several of the constructions used in geometrical drawing that belong to this latter class. Amongst these I think it must be said is the construction of a nonagon, and therefore also of an angle of 70°.-A. L. W.

[35434.]-Angle of 70°.-Allow me to inform "E. H. C." that his solution to the above is nugatory. He makes a very bold assumption, which ought to be considered as a hasty intrusion on geometry. The solution of this problem has occupied the minds of eminent mathematicians for centuries past, but as we now see their endeavours were in vain. It may benefit "E. H. C." to notice that along with this so-far considered impossible problem may be grouped the squaring of a circle and the reduplication of a cube.-E. K. DIXON.

linen over the cork. I then sank it into the sea 600 feet. When drawn immediately up again the cork was inside, the linen remained as it was placed, and the bottle was filled with water. I next made a noose of strong twine around the bottom of the cork, which I forced into the empty bottle, lashed the twine securely to the neck of the bottle, and sank the bottle. 600 feet. Upon drawing it up forced its way by the twine, and in so doing had immediately the cork was found inside, having with water. I then made a stopper of white pine, broken itself in two pieces; the bottle was filled long enough to reach to the bottom of the bottle. After forcing this stopper into the bottle I cut it off about half-an-inch above the top of the bottle, and drove two wedges of the same wood into the stopper. I sank it 600 feet, and upon drawing it up immediately the stopper remained as I placed it, and there was about a gill of water in the bottle, forced its way through the pores of the wooden which remained unbroken. The water must have stopper, although wedged as aforesaid; and had the bottle remained sunk long enough, there is no doubt that it would have been filled with water."J. B. W. OLIVER.

[35466.]-Cement for Ivory and Metal.— Plaster of Paris soaked in a saturated solution of alum, and baked hard. Grind to powder and mix with water for use.-ALBERT HALL.

solution of hyposulphate of soda is used for this [35472.]-Polishing Silver.-No. 1. A strong purpose with a brush. No. 2. Warm the articles, and coat carefully over with thin collodion diluted with alcohol, using a wide soft brush for the purpose.-ALBERT HALL.

[35478.]-Cutting Hardened Steel.-Use a small diamond, or at least carbonado, which is the "amorphous" diamond.-B. P. A.

[35483.] Square or Cube Roots.-I give as asked the examples worked out in logarithms: 1620. log.

3.2095150

Log. of cube Cube=

9-6285450 425152800

[35436.]-Shafting.-Allow me to thank your correspondents "Telescopic Tele," "Carl," and Willing," for noticing my query on Shafting," though I think their answers are not correct. But perhaps you will allow me to give a case in point. We have a machine at our place, for the driving of which we found it necessary to put a cone pulley on one shaft: the diameters are 143 in., 12in., and 10/16 respectively; on another shaft, the centre of which was 22 in. distant from the other, we had a cone pulley, the least diameter was 211in., the next 4in., and the largest 611/16 But we noticed that when we wanted to put the strap on the second speed, that is on the 123/1 and the 4in., it was about a lin. slack. So we had to have fresh pulleys made, the diameters of which are 7 in, 5gin., and 211in., and, though they are not exactly correct, yet they are near enough for all practical purposes. But still, I want the rule by which it can be answered at the first time without guess work.-LEES.

- As

[35447.] Pressure of Deep Water. neither of the answers already given are very firstclass, I will try what I can do. The bladder would not burst, because the pressure of the water will compress the air so that pressure inside and out will balance. If it had been a bottle, instead of a bladder, the pressure of the water would have broken the bottle inwards, or driven the cork in. According to "Natas," it would force the cork out. The bladder, if full of air to start with, would be crumpled up by the pressure, for the air would go into a very small space. At 14,000ft., allowing 30ft. to an atmosphere, it would occupy only 1-466th of the space it occupied at the surface.-PLONI ALMONI.

[35447.]-Pressure of Deep Water.-Owing to the yielding nature of the bladder, and the elasticity of the air within it, the pressure of the water would only cause the skin to collapse, the condensed air remaining inside, but it would not burst. At a depth of 14,000 feet the pressure would be somewhere about 872,524-8 lb. on a square foot. density, and hence the sides of the vessel have to In the case of a bottle the air within is at normal support the entire pressure of the water. The following account of some experiments relating to this subject, taken from a note to "Parker's Nat. Phil.," where the Baltimore Gazette is cited as the original authority, may be interesting:-"26th of September, 1836, the weather being calm, I corked an empty wine-bottle and tied a piece of

[35507.]-L. C. and D. R. Engines.-There above query on page 547. At the fourteenth line, are a few small printer's errors in my answer to the "Longridge Works" should read Longbridge Works, and at the first line of the second column, "Mr. W. Kirtley's Tank Engine" should read Mr. D. Kirtley, &c. My reply to query 35572 "Railway Engines" was initialed "G. L. S." instead of G. L. P. by mistake.-G. L. P.

[35510.]-Wheel Patterns.-Perhaps the folWhen the lowing rough sketches may be useful. cut into lengths about 1-16th of an inch longer than strips have been planed to proper thickness they are finished size and planed in a box (prepared for that purpose) to the required length (Fig. 1.) A tem

plet is then made in hard wood to the exact shape of the tooth and cut away in the middle to allow the pieces to fit tightly (Fig. 2), when with a little care they may be pared with great accuracy. I would advise "Pattern Shop" to get the "PatternMaker's Assistant," by Rose, which, I believe, was published in these columns some time ago.-FORT.

[35511.]-Cast Iron Rusting.-Cast-iron pans used for boiling linen yarn here are lime washed inside. The coat lasts a surprisingly long time considering its nature. The bottoms of iron ships are sometimes coated inside with a thin wash of Portland cement. Either of these might answer as a makeshift; but I think your safest plan will be to get an enamelled pan.-J. BROWN, Belfast.

be shifted without removing the glass or frame. At the back of the instrument a small screw will be found, showing through a hole in the case. By slightly screwing up or unscrewing the hands will be found to move forward or backward as may be necessary.-ALPHA.

[35611.]-Casting Steel.-Steel contains less carbon than cast-iron, and requires a much higher temperature to melt it. The great heat fuses the sand.-B. P. A. [35612.] Lever Escapement. "Seconds' Practical Watchmaker" gave some elaborate articles on the lever escapement about five or six

weeks back.-ALPHA.

a semi-cylinder, the elevation of the end of which is represented by A E B, and suppose it were required to describe on the plan the spiral line en veloping the semi-cylindrical surface in the length B D, measured parallel to the axis. Let the se micircle A E B be divided into any convenient number of equal parts, 1, 2, 3, &c., as in the diagram, and let the distance BD be also divided into the same number of equal parts; then, if from all the points in the semicircle lines be drawn parallel to the axis of the cylinder, and intersecting the corresponding lines drawn at right angles to the axis from B D, their mutual intersections will be so many points in the projection of the helix on the cylinder.-E. K. DIXON.

[35615.]-Force Pump.-Though more of an observer than a fellow-reader, I hasten to help where I understand what is wanted. It appears to me "Harmonious Blacksmith," among others, some years back gave solutions to this question in the ENGLISH MECHANIC, one being a hand-pump, another, if I remember right, was something like

[35616.]-Hardening Bicycle Bearing.-IF F. The jaws are kept together and made to I think C. S." (A. B. C.), may remedy this by retain the shackle-pin by means of the clamp, H, making the hub red-hot, and then rubbing the which is held in position by the pins, I I. In case wearing parts with potash.-FOREMAN. of overwinding the jaw hooks pass into the ring, C, [35616.]-Hardening Bicycle Bearing.-You but the projections, K K, of the clamp coming into cannot harden it if it is soft iron, but you might put the clamp stationary, while the jaws are being contact with the bottom flange of the said ring, hold a steel tube inside.-NATAS pulled through, the result being that the pins, I I, are sheared off and the jaw hooks released. The internal diameter of the ring being the same as the width across the jaw hooks, F F, the rope remains secure until the jaw hooks reach the top of the ring, when, by the action of the weight of the load they are forced open and so hook on to the top of the supporting ring, C, the end rope passing over the pulley.-VALENTINE.

[35620.]-Air-Pump Valves.-The piston in your air-pump is made of two parts, screwed together. Unscrew them, and on the bottom part you will find the valve, or the remains of a former valve. This you will find to be a piece of oiled silk; and if you remove it, and tie a double layer of oiled silk down in the same manner as the piece now on, you will find this part will work well; then take the bottom valve out, repair it in the same manner, and your pump will be effective. Do not attempt to alter the form of valvos; you would probably spoil the pump altogether. Better make good the valves now in the pump.-W. J. LAN

CASTER.

[35621.]-Saltpetre.-I have known many persons who have bought "saltpetre" from different places, and when I have examined it it has turned out to be nitrate of sodium, instead of nitrate of potash. And we know that there is a great differ

ence between the two salts; nitrate of soda is distinguished from nitrate of potash by its deliquescent property, a character that renders it quite inapplicable to some of the purposes for which the latter is employed. Perhaps our friend has been deceived in getting two salts at different places.-JNO. DEWHURST.

[35622.]-Electric Light.-Use as a conductor wire No. 16, and for the lamp artificial (pure) carbons, not thicker than one-eighth of an inch, for your current.-WIESENDANGER.

[35624.]-Vinegar Adulterated.-Boil down completely to dryness, with a little lump sugar. If sulphuric acid is present, the sugar will be blackened by being converted into carbon.-PLONI ALMONI.

[35626.]-Medical Coil. The cells you have don't work well. I would advise you to make the chloride of silver cell; they work much better for a medical coil than any other small form of battery I have used. During the past few weeks several answers respecting this cell have appeared, so that you can easily refer and find all the information you require to make them.-W. J. LANCASTER.

[35626.]-Medical Coil.-Use a saturated solution of bichromate of potash, to which you add onetenth of sulphuric acid. You can carry the bichromate as dry crystals.-WIESENDANGER.

[35628.]-Safety Hooks.-The safety hooks best known to the public are those of King and Walker, but I believe the latter signally failed this So I supyear, resulting in the death of two men. pose the former has now the precedence. The sketch will sufficiently point out the mode of appli

FICI

FIC.2

cation. Fig. 1 shows the hook in its ordinary working attached state. Fig. 2 shows the hook in operation after detachment from the rope.-T. E. J.

[35629.]-Mining.-Whether firing shots in the night time or in the day time, the proper plan is to commence at the return and work round to the intake, as the person firing the shots has a clear atmosphere in which to detect the presence of any gas; but were the shots fired from the in-take first, the

accumulation of smoke carried onward with the ventilating current would so vilify the atmosphere as to render the detection of gas extremely difficult, if not impossible.-T. E. J.

FIG. 2

[35629.]-Firing Shots.-In firing shots at night time I would begin at the return and work towards the intake, thus leaving the powder-smoke behind, and leaving a clear atmosphere for each shot.-C. M.

BOILER

the following:-A, 2in. plunger-pump, without valves if preferred, the bottom being connected with a cup by a pipe and tap, A-in. pipe, connecting pump and boiler, with ordinary steam stop-cock, B, and ball valve, C. Action:-Open taps B and A'; draw up plunger; close A'; force plunger down, till water which was first poured into cup (then cut off at A') rises high enough in boiler; close B; open A1; fill up water; raise plunger ready for more injection when required.-CEYLON.

[35616.]-Hardening Bicycle Bearing. Take your hind wheel to pieces (i.e., detach the spokes from the hub), and place the hub in the hands of some toolmaker or engineer who will caseharden it for you. A reference to back numbers will give you the modus operandi of the process of case-hardening. JOHN HAYES, Sutton, near Pres

cot.

the hook; Fig. 3 is a front view of the whole apparatus, with the supporting ring and clamp in section; Fig. 2 is an edge view of Fig. 3, with the supporting ring in section; Fig. 4 shows the apparatus applied to a pit in the course of being sunk. The hook consists of a pair of jaws, DD, working on a centre-pin, E, in such a manner that the weight of the load has a tendency to open the upper limbs, which clip the centre pin of the shackle, A. The upper limbs are formed externally with jaw hooks,

B

[35629.]-Mining.-It all depends upon the circumstances. If the pit is a gaseous one the intake would certainly be preferable, but the smoke might be offensive to the shafters or byemen. If the pit is free from noxious gases-at least, inflammable ones-it is really no matter where you begin, only allow a sufficient time to elapse from the firing of the last shot to the time of the workmen coming down, so as not to charge the workings with powder smoke to any great extent.-VALENTINE.