2HNO3 + 2H = 2 1⁄20 + 2NO2. 2. On being heated to between 100° and 200° C., it If the latter explanation is adopted we confirm it rises in beautiful vapours of an intense violet by this formulacolour, having a powerful odour. 2HNO3+6H = 4H2O + 2NO. Causes of Failure. If the zincs are not amalgamated you get too little current from the battery, and the zinc is wastefully consumed. The oxidising action of the battery causes the tops of the zincs and the binding screws and clamps to be continually covered with a non-conducting layer of oxides. These should, therefore, be filed clean and bright each time you are going to use the battery. When you have done your experiments. carefully clean out your battery, and never leave the solutions in it when you do not want the battery in action. Grove's battery is very compact, and as it gives a good current it is much favoured where money is no object. Amateurs, however, whose expenditure is limited, would prefer to make a Bunsen's battery, giving the same current strength at half the cost, or better still a bichromate battery. The working of both Gro ve's and Bunsen's batteries is rather expensive on account of the consumption of nitric acid; these batteries should always be placed outside buildings, for the fumes arising are dangerous to animal lite and destructive to metallic objects. In my next letter I will give instructions for making Bunsen's battery and the bichromate battery. I beg to thank "Madron" and "Agor" for their valuable suggestions. Th. Wiesendanger. ANALYTICAL CHEMISTRY-VIII. [15255.-1. This element is not known in the free state, but exists in combination with calcium in Huor spar (CaF), hones, and nearly all phosphatic minerals. It is also found in cryolite, a double Auoride of aluminium and sodium. Fluorides (M′F). 2. The fluorides of Sn and Ag are easily soluble in water; those of K, Na (NH4), and Fe are sparingly soluble; all others are insoluble. Fluorides of Am, K, and Na have an alkaline reaction, and all aqueous solutions corrode glass vessels in which they are kept or evaporated. 3. CaCl2 in aqueous solutions gives a transparent gelatinous precipitate of CaF2, which is scarcely visible till after the addition of ammonia, as it refractive rower is near y the same as that of the liquid. This precipitate, if it does not contain silica, dissolves with difficulty in HCl or HNO3, and is partially reprecipitated by AmHO. 4. BaCl2 or Pb (NO3)2 give white voluminous precipitates. 5. All fluorides are decomposed by strong H2SO4, with evolution of hydric fluoride, a gas somewhat resembling HC in its general properties. It is, however, expecially characterised by its power of attacking and corroding silica or silicates, and it is upon this property that the usual tests for fluorine are based. 6. The best method of showing this reaction is to mix some of the finely powdered substances with strong H2SO4 in a leaden cup or platinum crucible, these being almost the only metals which are not attacked. Cover the convex side of a watch glass with a thin coating of wax or paraffin, and trace a few lines upon it with a needle. so as to expose the glass. Place this upon the top of the crucible, with a little water in it, to keep the wax from melting, and warm the bottom of the crucible very gently. After a time, varying from a few minutes to an hour, according to the quantity of fluoride present, remove the glass and clear off the wax, when the lines will be found engraved or "bitten in " upon it. When the etching is very faint, it becomes much more distinct when breathed upon. 7. The foregoing method is not applicable when silica is present in any form, as a gaseous fluoride of silica (SF) is formed which has no etching power. SF is, however, decomposed by wat r with formation of hydrated silica, and so may be detected by bolding a drop of water in the crucible suspended at the end of a thick platinum wire, when it will be dimmed by the formation of a pellicle of silica on its surface. 8. Small quantities of fluorine may also be detected by the blowpipe in the following manner :-Damp the powdered substance very slightly, mix it inti mately with microcosmic salt, and heat it at the end of a glass tube open at both ends in such a manner that the flame may be partly driven into the tube. If fluorine be present, HF is volatilised and condenses along with water in the cooler part of the tube. On evaporating the water, a dull spot is found where the glass has been corroded by the acid. Iodine (I.) 1. Iodine in the solid state is a black metalliclooking crystale body; stains the skin brown on contact, and is only very slightly volatile at ordinary temperatures. 3. Free iodine, both in vapour and solution, forms a deep blue compound with starch paste. This reaction is exceedingly characteristic and delicate. Care must be taken, however, to keep the solution as cold as possible where minute quantities are being tested for, as the colour of this compound is destroyed on heating. 4. Iodine is but slightly soluble in water, to which it communicates a yellow or brown colour. This solubility is greatly increased by the presence of a soluble iodide in the solution. 5. In ether or bisulphide of carbon, iodine dissolves with a beautiful rich violet red colour, inclining to purple when a considerable quantity is present. Iodides (M'I.) Soluble iodides give the following reactions: 6. AgNO3, primrose-yellow ppt.; issoluble both in HNO3 and Am Ho. 7. Poac, bright yellow ppt.; soluble in a large excess of boiling water, and crystallising on cooling in golden scales. 8. HgCl2, scarlet ppt.; soluble in excess of either reagent. 9. PtC14, brownish red colouration, and after some time a brown ppt. 10. Salts of palladium, black precipitate. 11. A bead of microcosmic salt saturated with CaO, communicates a beautiful green colour to the blowpipe flame on the addition of an iodide. 12. Solid iodides are decomposed by heating with strong HSO4, a little MnO2 or K2Cr2O7 being added if necessary. The iodine comes off in vapour and is easily recognised by its characteristic colour. 13. Iodides in solution are best decomposed by chlorine water, hypochlorite and HCl, or nitrous acid, and the liberated iodine detected by reactions 3 and 5. Care must be taken not to add too much chlorine, as free iodine readily combines with excess of that reagent, and so cause the test to fail. 14. Iodates (M'IO3) are easily distinguished by their evolving oxygen when heated, and giving free iodine on treatment with dilute H2SO4. Nitrogen. 1. With the exception of ammonia (NH3), the reactions of which have already been given, the only inorganic compounds of nitrogen of any importance are the nitrates and nitrites. The former are derived from nitrogen pentoxide (NO), and the latter from the trioxide (NO), these being the only two oxides which form acids. Nitrates (N'NO3) 2. Nitric Acid, when pure, is a colourless fuming liquid, but has usually a yellow tinge from the presence in it of some of the lower oxides of Litrogen. It acts as a powerful oxidising agent, couverting tin and antimony into white stannic and antimonic oxides, arsenious acid into arsenic acid, and ferrous into ferric salts. 3. All nitrates are soluble in water, and therefore cannot be obtained by precipitation. They are all decomposed by sulphuric acid with liberation of nitric acid, and as most of the reactions used as tests for nitrates require the HNO3 to be in the free state the solution must first be mixed with H2SO4. 4. Nitric acid, or an equivalent mixture of a nitrate with H2SO4, when heated with metallic copper, evolves nitric oxide, which immediately combines with the oxygen of the air to form reddish brown fumes of the trioxide (N2O3). The best way to observe small quantities of these vapours is to look down into the tube placed over a sheet of white paper, when a reddish-yellow colour will be seen. 5. Indigo solution is immediately bleached when heated with HNO3. To apply this test, colour the liquid light blue with indigo solution, and then add twice its volume of strong, pure H2SO4. 6. Ferrous sulphate reduces HNO3 to nitric oxide, which dissolves in the solution with a deep brown colour. In applying this test, shake up a portion of the solution with a few crystals of FeSO4, and then pour some strong H2SO, down the side of the test tube in such a manner that it will form a sepa rate layer at the bottom, when a brown or red colour. tion will be produced where the two liquids come in contact. This is called the "brown ring" test, and is exceedingly delicate. As the colouration is destroyed by heat, the solution should be kept as cold as possible. 7. If a solution of a nitrate be mixed with a few drops K.FeCys, and a small quantity of HCl, heated to 71°C, and slightly supersaturated on cooling with an alkaline carbonate, a nitroprusside is formed, which, after filtration, gives a transient purple or violet colour on the addition of a few drop of AmgS, or other alkaline sulphide. 8. Solution of a nitrate warmed with excess of HC, acquires the property of dissolving gold leaf, the presence of which in solution may be d tected by the purple ppt. produced by a mixture of stannons and stanbic chloride. 9. Nascent bydrogen, evolved by the action of KHO on Al, or Zn and Fe, by bringing water in contact with sodium amalgam; or by the action of the copper zinc couple, transforms nitric nitrogen into ammonia, which may be detected by Nessler's solution. All ammoniacal compounds must of course be absent or previously destroyed by boiling with KHO. 10. Carbolic acid is converted by HNO3 into reddish brown nitrophenol. To apply this reaction, dissolve 1 part of phenol in 4 parts strong H2SO4, and dilute with two parts of water. Evaporate the solution to be tested on a porcelain crucible or cover, and allow a drop or two of the reagent to fall upon it at a temperature not exce ding 100°C., when a reddish brown colour is immediately produced. The reaction is exceedingly neat, delicate, and characteristic. 11. Traces of HNO3 may be detected by evaporating the solution to dryness, moistening with a drop of pure H2SO4, and moving about a fragment of brucine in the liquid, when a rose red colouration ensues. This test will show the presence of HNO3 in 1 c.c. of a liquid containing only 1 mg. per litre. 12. Mix 1 c.c. of pure H2SO4 on a watch-glass by drops, with c.c. of solution of aniline sulphate, and bring a drop of the liquid to be tested to the edge of the acid. If only a trace of HNO3 be present deep carnation red streaks and curves make their appearance as the liquids slowly mix, and the entire liquid becomes rose red. If the quantity of HNO3 be larger the colour varies from carmine red to brownish red or brown yellow. 13. All metallic nitrates deflagrate when heated on charcoal. Nitrites (M NO2). 14. All xitrites, except those of Pb, Ag, and Co, are readily soluble in water. They are either colourless or slightly yellow. Exposed to the air they absorb oxygen and are converted into nitrates. KNO, and NaÑO, have an alkaline reaction. 15. Nitrites resemble nitrates in many of their reactions, but may be readily distinguished from them by their reducing and oxidising qualities, of which the following are most characteristic: 16. Permanganate of potash is instantly decolourised, and the red colour of K2Cr2O7 gradually charged to greenish-blue by nitrites. They also reduce AuCl, and HgNO3, giving with the former a brown precipitate of Au, and with the latter a grey precipitate of Hg. The oxidising action of nitrites is best shown by their acidulated solutions giving an immediate blue colour with KI and starch. Nitrates give neither of these reactions. 17. Brown nitrous fumes are evolved when nitrites are decomposed by HCl or H2SO4. 18. With aqueous solution of CaSO4 a very characteristic apple-green colouration is obtained. 19. Mix the liquid to be tested for HNO with K,FeCy, and acetic acid. Boil, cool, and add AmS, when a blue colouration is produced if nitrites are present. 20. One of the most delicate of all the tests for HNO, and one which affords a certain distinction between nitrous and nitric acids, is to evaporate the liquid to dryness and triturate the residue with two drops of aniline sulphate, when a distinct odour of phenol will be emitted. 21. Greiss' test" is a solution of diamido-benzoio sulphate, which, with a large quantity of HNO produces a brown-red amorphous precipitate, and with small quantities a more or less strong yellow colouration. This reaction is said to be equal to the detection of 1-5,000,000 of HNO. 22. Reactions 6, 8, 9, and 12, for nitrates, may also be advantageously used for the detection of nitrites, which give similar results. The only difference is in the case of No. 6, in which a brown colouration is obtained without the addition of an acid. Ciar Vohr. (To be continued.) ANALYTICAL CHEMISTRY. [15256.]-IN answer to the criticisms of "Nonsach" (15217) on my letters on the above subject. I have to inform him that they are not only written for chemists, to whom the greater part of them may not be new, but for those who occasionally require to apply chemical tests for various substances, and do not care to go to the unnece sary expense of buying special books on analysis; and also that all our readers may know where to refer for informa tion on such matters without overhauling all the back numbers, where probably they may not find anything to assist them. What I have as yet given are simply the reactions which the elements show when pure salts are used, but among these will be found in nearly every case some test which will show the presence of the element in almost any solu tion, although I will of couree afterwards give directions for the examination of complex mixtures. Any one can understand that if a black precipitate be obtained with Nessier's solution, something must be interfering with the normal reaction, and conse queatly some other test must be tried for its detec tion; but that it can be no evidence against the presence of ammonia. As to the source of my intormation, I may say that it is taken from no par ticular book, but is the result of a number of abstracts taken a short time ago from all the standard works on the subject, Fresenius included, so that it may be taken as reliable, and particularly in the matter of special tests (nearly all of which I have confirmed myself), as complete if not more so than anything as yet published. In regard to Mr. Allen's comparison between my "Analytical Chemistry" and Mr. Clements' "Identification of Organic Bodies," I venture to think that the majority of our readers will consider the reactions of copper or nitric acid quite as important, as far as general utility is concerned, as those of myosin, chloropropionic acid, and similar substances, of which few of them have heard, and regarding which still fewer take the slightest interest. Ciar Vohr. A DELICATE MAGNETIC NEEDLE. Magnetic needle suspended by a method new to me. The horizontal needle drops from the other if not carefully handled, but is for a time the most sensitive instrument of the kind ever seen by the writer. On passing it from top to bottom of all the vertical iron bars within reach, the needle has proved these bars to be temporary magnets by influence of the earth's magnetism. One end of the needle oscillated before the upper half of each bar tried, but the other end of the needle vibrated before the lower half of the bar. The action was just the same in principle as if the needle had been passed up and down in front of an upright permanent magnet. On testing with other needles, differently suspended, they pointed with either extremity to the whole length of the vertical iron bar, not being able to indicate that the iron was magnetic through the inductive action of the earth. The light covering is necessary for the centre of the horizontal needle to prevent its slipping. A NEW BICYCLE. J. Trott. bricks have been laid in a row, and ridden over PROFESSOR BELL AND ENGLISH i point in the circuit, no safety-valve is needful, or that if a boiler is cram full of water there is no room for steam, and therefore it cannot burst. I can only say in conclusion that the three mechanics referred to-the turner, the plumber, and the mason -are all first-rate, experienced workmen when working in their own grooves. Southwood. FROZEN PIPES AND DELUGED valuable and practical hints on house matters. 66 MICROSCOPICAL. A Small Property Owner. P.S.-A fair estimate and list of prices for plumbIf the charge can be substantiated, the defect in the British workman, if I mistake not, will be founding work would be a great help for country people to be not so much in the absence of of technical away from town advantages and town prices. education as in the lack of power to make the mind which they are accustomed, but a piece of new work serve the hands. The hands can do anything to [15261.]-SOME time since Mr. Theodore Izod such as a model of an invention must necessarily be beyond the scope of the cleverest pair of hands work-wrote a letter on microscopic histology, which ening automatically. couraged the hope of further communications on the same subject It is matter of regret that this hope has not been fulfilled, for the subject is at least as interesting, and, I venture to think, mere impor tant than the marking of diatoms. The study has also the advantage of being practicable with objectives of comparatively moderate powers and angles, and hence of moderate cost. The action of hardening and colouring fluids on the different tissues offers a field for search interesting to the chemist as well as to the physiologist. May I hope that the subject will be resumed, for by correspondence in many small points of manipulation are brought out, which are omitted in the textbooks? I should feel greatly obliged personally if some of your numerous correspondents could refer me to a work with information on the moulds concerned in fermentation (and also, if possible, on the putrefaction organisms), such as to enable me to identify them. Plates of course are essential, possibly Pasteur's work on brewing might do. be obtained, second hand by preference? With your leave I will give two examples of the [15258.]-KNOWING the great interest our sub- it would be different. It being useless to argue Whero can this "P. T. O." (35160) will find that many crystals can be preserved in the ordinary way in balsam or dammar, others simply dry under a glass cover. The salts should be dissolved in pure water, and a drop allowed to separate spontaneously on the slide. Curious effects may also be obtained by evaporating by the aid of heat. Some nitrate of aniline among my slides bas formed a series of parallel equidistant lines with objects between them singularly like Arabic characters, and of course glowing with the most gorgeous colours under the polari cope. For this purpose I may caution "P. T. O." against getting too thin a crystalline layer. With some bodies a thin layer barely shows white on the dark ground, where a thicker gives brilliant colours. Often repeated experiment is required to get the best effects. Picric acid, picrate of potash, nitrate of aniline, nitrate of potash, and borax are a few of the compounds giving good results. [15262.]-I Do not intend commencing the monthly notices until the appearance of spring's first blossom" for reasons which will be stated at the proper time. In the meanwhile, it may not be out of place to give a few hints on the different methods of mounting used by microscopists-viz., opaque, transparent, and fluid; in the latter division "C. C. Hawks" (let. 15209) will find all he requires. As regards cells and trays for opaque objects (or those vi wed by refracted light), the following plan was adopted by a friend and myself some years ago, March Brown. THE CONTINUOUS BRAKE RETURNS The [15263-In continuation of my letter, p. 347, I send an epitome of the Railway Returns (Continuous Brakes) Act, which was passed June 17th, 1878. The Act provides for returns respecting continuous brakes in use on passenger trains. returns shall be made for the six months ending on the last day of December and the last day of June in every year, or on such other days as the Board of Trade from time to time direct, and shall be made within fourteen days after the expiration of each six months." "Any railway company who fail to comply with this section shall be liable on summary conviction to a fine not exceeding £5 for every day during which the default continues." "Any person who makes or is privy to the making of a return' which is to his knowledge false in any particular shall be liable to a fine not exceeding £50." The forms of return supplied by the Board of Trade require the companies to answer the following important questions: 1. Whether the brakes are instantaneous in action, and capable of being applied by engine drivers and guards. 2. Whether self-acting. 3. Whether capable of being applied to every vehicle of a train. 4. Whether in regular use in daily working. 5. Whether the materials employed are of a durable character, easily maintained and kept in order. The amount of stock fitted with continuous brakes. The amount of stock not fitted, and the amount fitted during the last six months. The special rules under which the brakes are worked must also be given. All cases in which continuous brakes have, from any cause, failed to act when required to be brought into action, and all cases in which continuous brakes have not been used on any passenger train, must also be shown in the return. The answers given by the railway companies to the five questions show that there is a consider able difference of opinion as to what is meant by the words "instantaneous in action," especially in reThe copy of Captain Galton's table upon p. 225 shows the time taken to apply the vacuum brake. It will be seen that 14 seconds were required to put this brake "full on upon a train of 13 carriages, The Great Northern Company state "that the brakes are instantaneous in action." The NorthEastern say that Smith's brake is "nearly instantaneous." The Midland answer is simply "No." And the Great Southern and Western of Ireland state that this brake "is not instantaneous." ference to Smith's vacuum brake. omissions in the Board of Trade "returns." For the year 1855, and published in their Transactions. This right-angled prism, connected with the under side of the slide by a film of oil of cloves, was either mounted in a fitting, or stuck on separately to the slide with the oil or Canada balsam, and is one of different methods of a newly-announced principle of illumination, in which I first made use of the top surface of the glass cover of balsam-mounted objects as a total reflecting surface, or speculum for illuminating the underlying objects viewed with the highest powers. I acquiesce in the encomiums bestowed upon the prism. especially the fa that the greater proportion of Many railway officials laugh at the idea that they shareholdera' Dec. 18th. money. C. E. S. THE TUBE PNEUMATIC ACTION FOR [15264. This action, which is so suitable for the B This is not, however, superior to the more recent reflex" illuminator, which is a compound lenticular arrangement, with the spherical aberra tion carefully corrected, so that the whole light is concentrated on a small atom or diatom under observation. In the prism it is not at all necessary that the light should enter the surface at right angles. A square block or cylinder of glass will serve equally well, as chromatic effect will not be apparent, and total reflection quite as effective. J. D. C." makes a misstatement, or is under an illusion, when he asserts that the position originally taken by the parties he names, in the aperture ques tion, has become the received doctrine in all countries. I cannot expect those who first took an adverse position in the "Battle of the Angles" ever to acquiesce in any subsequent demonstrations and facts advanced by me; the argument was too controversial for any such concession. A few months ago the discussion was revived in the ENGLISH MECHANIC. This has again called attention to the principle of measuring the angles of aperture of microscope object-glasses, and the subject has since been taken up in America by experts well versed ia optics, who took no part on either side in the early controversy, and therefore fully recognise and admit C the false measurement of oblique angles outside the central ones, which indicate errors largely in excess of the true angle. F. H. Wenham. OPTICAL DEFECTS AND DISEASES OF In the sketch, a is the pedal, b is a small windchest, supplied with high pressure wind; upon de pressing the pedal the top valve on the small chest is pressed down close and the lower valve is opened; the wind is admitted into the channel, and travels along the pipe, c, into the disc valve, d. This valve is made by boring a hole 4in. in diameter, and about rubber, in the centre of which a small wooden plate Lancaster, who has undertaken to advise your an inch deep; the top is closed with a piece of india[15266.]-I SEE your profuse contributor, Mr. is fixed with a pin rising from it. The wind can raise readers on these subjects, proposes to write an the disc about half an inch. When it rises it pushes article on "Vision, and how to preserve it," for up one end of the lever, e, which closes the valve,f, your pages. I hope he will do nothing of the sort and opens the valve, g. Wind is thus admitted to the-firstly, because, judging from his unique theory pneumatic bellows, and the soundboard pallet opened of the effect of tinted glasses on the nerve elements in the usual manner. One great advantage of this action is that as many branches may be led from the tube, c, as may be required, and portions of the pedal organ placed wherever it is most convenient. Where a manual organ is required to be placed at action. The divided organ in St. Paul's Cathedral I may mention that there are some important a great distance from the manual the action may be made in a similar manner, and is much superior to instance, the West Lancashire, and the Glasgow, the electric action, which is often getting out Bothwell, Hamilton, and Coatbridge Railways have of order, besides being very expensive to keep in adopted the Westinghouse automatic brake, and it has been fitted to the whole of their passenger trains for a considerable time; it is therefore strange that neither of these railways appears in the official list, more particularly as the working of the brake upon both lines has been so very satisfactory. It will also be observed that the train upon the London, Chatham, and Doser Railway, fitted with Smith's vacuum brake has not been mentioned in the "return." On Thursday last (Dec. 12th) the Right Hon. W. E. Baxter brought the subject of continuous brakes before the "House of Commons," J.D.-W. THE SO-TERMED "WOOD WARD PRISM." of the retina I fear your readers would have much hypothesis; secondly, because his attempt to input before them as fact which is utterly unsupported must end in failure to him and disaster to them. struct the public in self-adjustment of optical defects These defects are so obscure in very many instances that it needs the minutest examination of a skilled oculist, and the use of atropia, of the ophthalmo scope, and of test objects, to make them out. Not every oculist, few opticians, and no general surgeons, understand the subject, and as for patients, the most intelligent of them are completely misled by their sensations as to the causes. My experience in such matters is not small, and I assure you that at least two-thirds of the money I earn by remedying these defects comes to me directly as the result of persons attempting to adjust themselves, and not making allowance for accommodation, derange ments, or for their own personal circumstances-in fact, from treating the eye simply as an optical instrument and ignoring its vital conditions. As t would be utterly impossible for your correspondent to make the average reader estimate these, neither he nor I would do good by making the attempt. Much already written in your replies to queries on this subject was pernicious pseudo science. An Fye Doctor. ELECTRIC LIGHT FOR THE HOUSE. [15267.1-THE sentence of "Sight " about rediscovery (Let 15233) may well be quoted against himself. Forty years ago a coil of wire was wound round a piece of wo d, and rendered incandescent by a galvanic battery, in order to give a lecture demonstration of the heating power of the battery by setting the wood in a blaze. In order to render the light of the coil visible at a distance, it was wound round something white-presumably a chalk crayon. Neither this principle nor idea can be secured in a patent. "Sight," if he pleases, can claim some particular nostrum or compound to go within the coil, but I think that he had better save his money, as the plan will be of no practical utility, and the patent will not be worth the parchment that it is on. F. H. Wenham. I the foot will give a rocking mowa to the battery, S W B C Any of your readers trying this method will find success certain and, expense trifling in proportion to the brilliancy of the light. W. KING'S PATENT ELECTRIC LIGHT OF 1845. It is probably for some such contrivances as this, 1:268]—I REGRET that I am compelled to trouble TOU so often about so little; but really the letter 15233, page 396, requires some notice to be taken of it. I am very glad to learn that some one has made an improvement in lighting by electricity; but, unless it is a system complete within itself, I am sorry he patented it. Progress is hampered by petty patents. The letter seems to me to suggest that I have borrowed from the ideas of this inventor. As bis specifications are not to be issued for a week or two it is evident such could not have been the case; but the converse is possible, although I do not for a moment suppose that such is the case. My invention, if such it can be called, was described in our leading Scottish daily some time since. I do not know the date, as I cannot lay my hands upon the paper; but some of your readers will have seen it. It was about six weeks ago, I think. I explained then to many who called the principle of improve ments in it not made public. Now this gentleman has a perfect right to patent lighting by any par: ticular material or arrangement of material not mentioned by me; but the principle of lighting by an incandescent non-conductor was public property about two months before his specifications are due, and to that extent they are invalid. It was my private property six months before. I may say that I heat wire to a high temperature from the secondary coil, suitably wound, aided by a condenser, and that I use an automatic current reverser of my own design with this apparatus, and so can work many lamps in circnit without breaking contact. I am getting suitable coils made for this purpose. I shall be glad to get the ten-shilling lamp made for any one, as promised; but cannot undertake to give information by private letter. 136, Bothwell-st., Glasgow. Juo. M. M. Munro, [15269.7-I wish to describa for the benefit of those readers of the ENGLISH MECHANIC who may wish to light their rooms by electricity a very simple and tolerably economical method of doing so. of The inclosed diagram shows B, a bell-glass resting in a vulcanite tray, V, attached to a wooden stand, $; the 2 wires, W, pass air tight through bottom of tray and stand to the two poles of an ordinary 3 or 4 cell bichromate battery; Cis a very slender pencil gas carbon connecting the two ends of the wires; P is a metal cup to hold a bit of phosphorus. Having made the lamp as sketch, proceed as follows:-Nearly fill the tray, V, with water, light the phosphorus in P, and put the glass cover, B, in its place; do this a few hours before the lamp is wanted for use. The phosphorus unites with the oxygen in the bell-glass and becomes converted into phosphoric acid, which is gradually absorbed by the water, and nothing remains but pure nitrogen in the lamp. Connect the ends of the wires to the two poles of the battery, and the carbon pencil, C, will glow with a brilliant white light, and remain in that state unconsumed, owing to the absence of oxygen Of course any form of battery may be used. I prefer the bichromate in a trough form, and mounted on rockers, and the whole placed on the floor under the table, so that an occasional touch of gas. FIG. 1. W. Mattieu Williams. FIG. 2. This may be accomplished by the ordinary process of the goldbeater; but a more accurate method is to place a piece of platinum foil between two thick plates of rolled copper, and reduce the whole to a thin sheet by rolling, when on separating the copper pieces, the platinum leaf will be found of uniform thickness in every part. In this way it may be obtained so thin that on holding it before a printed page the letters can be distinguished through it. A strip is to be cut from one of these sheets of a width proporcionate to the quantity of the current, which, with Daniell's cells, 20in. high and 3in. in diameter, is about one quarter of an inch, and of a length proportionate to the intensity, which of course varies with the number of cells. Great care must be taken to cut the platinum strips of an equal width throughout, and with a clean edge, as, if this is not carefully attended to, the strip will be unequally heated, and will be fused in one part before the other parts have obtained a sufficiently high temperature to produce a brilliant light. The platinum strip is now to be suspended between two forceps in an instrument made for the purpose, one form of which is shown in section in the engraving annexed, and marked No. 1. A is a square brass bar fixed into the wooden stand C, having a binding screw, F, attached to its lower end. The two arms, E D, are attached to sockets which slide on this bar, so as to admit of their being placed at different distances from each other. They are both bent at right angles, as seen in the figure, and terminated by broad forceps tipped with pla tinum. These forceps are closed by the milled screws, HI; the arm, C, has a rod, N, with a screw cut on it passing through it, and by means of the two nuts, B B, working on this rod the arm may be adjusted to any required height, and the distanes between the forceps thus regulated. The rod passes through the stand, and is attached to the binding The socket, K, is lined with ivory, or screw, G. some other non-cor ducting substance, so as to prevent any metallic communication between the arm, E, and the bar; Sis the strip of platinum leaf which is first clamped in the upper forceps; the arm, E, is now adjusted to any required height, and the lower forceps are closed so as to clamp the lower end of the strip of platinum. It may now be included in the battery circuit by attaching one of the wires to the binding screw at F, and the other The current should be one of conto that at G. siderable intensity, and the distance between the forceps should be sufficient to prevent the platinum being fused. The distance may be lessened by raising the arm, E, and shortening the strip of plaattained by increasing the intensity of the current. will bear without fusing; or the same object may be tinum, until it attains the highest temperature it The glass shade, R, which serves to screen the platinum from currents of air, dust, &c., may then be placed over the apparatus, as seen in Fig. 1. Carbon Conductors.-When carbon is used it becomes necessary, on account of the affinity this substance has for oxygen at high temperature, to exclude from it air and moisture. To accomplish this in the most perfect manner it should be enclosed in a Torricellian vacuum. One form of the apparatus for this purpose is shown in section in the figure As King's specification has considerable interest No. 2; a, is a glass tube, similar to those used for at the present time we reproduce the abstract from barometers, except that it has its upper end enlarged the Mechanics' Magazine:into a cylindrical bulb, and a stout platinum wire Metallic Conductors.-The metal most advanta-sealed in at the top A small cup for holding mercury geous for the purpose is that which, while it is fixed on the top of this wire, whose lower end screws requires very high temperature for its fusion, has in the iron-piece, d; to this piece the forceps, ƒ, are but a feeble affinity for oxygen, and offers a great h, by the porcelain rod, i. The forceps, 9, are attached, and it is connected with a similar piece at resistance to the passage of an electric current. Platinum, though not so infusible as iridium, has attached to h, and clamp the lower end of the carbon but little affinity for oxygen, and offers a great piece, c, which has its upper end held by those at f; resistance to the passage of the current, and as it is and extends to the bottom of the tube; the tube is n is a copper wire which is fixed into the piece at h, filled with mercury in the same manner as a barometer, the usual precautions being taken to expel the air; its length, independent of the bulb, should be about thirty inches, so that when it is inserted in a cup of mercury a vacuum will be formed in the bulb. The instrument is included in the battery circuit by connecting one of the wires from the battery with the cup fixed on the wire, e, and the other with a wire which passes into the mercury in the cup at the bottom of the tube. The circuit is thus completed by the column of mercury, and when it is depressed in the tube by the formation of vapour of mercury in the bulb, the connection is preserved by the copper wire, n; that form of carbon on the inte1ior of coal gas retorts, which have long been used, is well suited for this purpose, and it may be worked into the form of either small pencils or thin plates by the aid of the saw and file. As carbon will bear a very high temperature without fusion or volatilisation, a much more intense light can be produced by this means than by platinum. intervals. When the apparatus is suitably sealed it may be applied to submarine lightning, and also to the illumination of places where it is necessary to guard against the inflammation of highly combustible or explosive compounds-as in powder magazines, mines, &c. When a current is of sufficient intensity two or more lights may be made in the same circuit, care being taken to regulate the power by increasing or diminishing the number of cells-if a voltaic battery is the source of electricity, or the number of armatures-if a magneto-electric machine be used, so that the united resistance of the strips of platinum or carbon shall be sufficient to prevent the passage of such a quantity of electricity as would destroy them. Claim.-"The application of continuous metallic and carbon conductors intensely heated by the passage of a suitably regulated current of electricity to the purposes of illumination as before mentioned." SINGLE V. COUPLED EXPRESS [15271.-I have to thank "C. E. S." for his answer (let. 14728, p. 581, Vol. XXVII.) to my letter (let. 14377, p. 269), and for the interesting information and arguments he has adduced on his side of the long-debated question-"Single v. Coupled Express Engines." I must ask him to believe that even if I do not accept his able demonstration as final and conclusive, I am not arguing merely for argument's sake, and trying to raise idle quibbles, but that I am, like himself, sincerely desirous to see this problem satisfactorily solved, if indeed it admit of any other solution than that both classes of engines are equally excellent. Let me repeat that "I am no special pleader for single engines;" indeed, some years ago I was strongly in favour of "coupled," and it was only my ocular evidence of the splendid work done by singles " on the G. W., G N., G.E, L. & N.W., and S.E. lines that couverted me in their favour. Nor do I now advocate the exclusive use of "singles " even for express traffic, but I do require more evidence than yet has been brought forward by "C. E. S." and others on his side to convince me of the superiority of "coupled " engines in the face of the admitted facts which I cited at some length in my letter above referred to (pp. 269 & 270.) used. Bat has he not a "term" too many here? I am aware that such conclusion necessarily is, to some extent, fallacious, because the argument as given does not contain all the factors in the problem; but I deal with it as presented by "C. E. S." Let me ask, however. why does not some distinguished locomotive superintendent try the experiment of combining large cylinder power with a moderatesized "single" wheel? For instance, why not try one of the Midland bogies, cylinders 18 x 26, with 7ft. single drivers ? Or suppose one of the G.N. engines, with 18 x 28 cylinders, were tried with 7ft. wheels (instead of 8ft), which would give a tractive force of 1081b. I believe that such experiments might lead to useful, and, perhaps, unexpected results. One thing is well known-that several 7ft. coupled G.N. engines have been converted into "singles," and, thus converted, have proved most useful express engines, running both the Leeds and the Scotch express punctually, although timed at 51 miles an hour. Another fact which occurs to me also seems in point. I believe that the G.W. "single" engines of the Great Britain class, and the G.W. First let me venture to point out that "C. E. S." is not quite accurate when he credits me with the allegation that "coupled engines could not keep time with the G. W. or G.N. expresses." I never said they could not. I simply pointed out that it had not been proved that they could-a very different and quite maintainable contention, which the other coupled engines of the Waverley certainly would not have been, for I have no right class, are almost identical in every respect but one, whatever to assert that "coupled engines could not viz., that the former have 8ft. single drivers, and keep time" with these trains, because there is no the latter are 7ft. coupled, both having cylinders absolute practical proof for or against. I freely 18 x 24. I was very much srruck some years ago admitted, and admit, that theoretical arguments with the circumstance that when the 7ft. coupled strongly support the affirmative view; but I re-engines occasionally took their turn on the express marked that judging from the work actually known or fast trains they never seemed able to run to time, and recorded to have been done by these engines, whereas the 8ft." singles," identical in all other experience did seem to throw the weight of evidence respects, but with smaller tractive force, always on the negative side. And I quoted numerous in- appeared able not only to keep time, but to make stances in support of this view. "C. E. S. " argues up a large amount of lost time when late in starting. very cleverly that if a "single" engine with 7ft. Of this last I have given instances in former letters. drivers, and cylinders 17 × 24, can keep time with the Again, I recollect at one time a new fast train being G.N, expresses, there is no reason why a "coupled" put on which had to maintain a speed of 40 miles an engine with 7ft. drivers, and cylinders 18 × 26, should hour up a three miles continuous bank of about 1 in be unable to do so. Quite true so far as it goes, 120, beginning half' a mile from a junction through but he forgets that this is begging the whole which speed had to be slackened to 15 miles an hour. question. Of course an engine with 18 x 26 cylinders It was supposed that the ordinary "single" engines ought to be better able to accomplish a given amount could not do this, so the train was run at first by of work than one 17 x 24, cæteris paribus, but if vesy powerful four-coupled goods engines, which you couple the 7ft. driving wheels to 7ft. trail-kept time well, but had to run rather faster than ing wheels, you introduce precisely that difference usual through the junction. A "single" express which is the subject of the present discussion-engine, with wheels and cylinders of same size as "coupled engines v. single." It stands to reason that the engine with larger cylinders should be more powerful than one with smaller cylinders, provided both be "single," or both be "coupled." The question, however, obviously is-Wou'd not coupling the wheels increase the power of haulage at the expense of the attainable velocity ? If a 7ft. "coupled" engine be unable to keep pace with a 7ft. "single" engine with smaller cylinders, it can be only because the former is coupled, and impeded by being so coupled. Now I do not say that the coupled engine could not keep pace with the " single, but I cannot help saying that the weight of practical evidence as to work done seems to tend this way. "C. E. 8." has taken the trouble (for which again I thank him heartily) to compile three interesting and instructive comparative tables, show. first, the speeds, average and actual, of the taatest trains, respectively, on the G. W., G.N., and Midland; second, the resistance to be overwe on those three lines respectively, taking into sideration the relative loads and gradients; d. the tractive force exerted by the respective . He shows that whereas in point of speed the ranks first, G.N. second, and Midland third, versed as to both the resistance to the tractive force of the engines the goods engine, then was tried, and maintained 45 At the same time, so far as the evidence goes, I must adhere to my previously expressed opinion that it preponderates in favour of the "singles." In the cases adduced we see the "single" engines varying only between 45 miles an hour up banks and 60 down; the coupled ranging from 35 miles an hour up banks to 65 and 70 down. The 35 miles an hour, too, was the average up a 5 mile bank; thus, as the speed at the bottom is stated to be 50 miles an hour, it is plain that at the top it could not have been much above 20, while the G.N. starting an SA mile bank at 50 miles an hour had not fallen below 40 when the top was reached. "C. E. S." once expressed great admiration of the work done by an engine which maintained 49 miles an hour down the Desborough bank and up the Kibworth bank. No doubt it was very creditable, and would suffice to keep time with the Midland express at 47 miles an hour, but it would not have been nearly fast enough to keep time with a G.N. express at 51 miles an hour, which would have arrived very late unless a much greater speed than 49 miles an hour were run. I presume that all parts of the Midland line are not equally infestel with banks, yet over no portion is a speed run near y equal to that of the G.N. expresses. Nor can I understand "C. E. S." calling the G.N. a "level" line, even comparatively. Refer ring to the sections given by himself, I find a 2 mile bank of 1 in 105 and 1 in 110 at starting, then a bank of 1 in 200 for 84 miles; then numerous other banks of 1 in 200, several extending for from 3 to 5 mile continuously; others of 1 in 150, 1 in 140, and even 1 in 100, all between London and Peterborough, over which heavy expresses average 51 miles an hour. I do not know the Midland gradients, but" C. E. S." quotes one of "1 in 120 for 3 miles "-not excessively formidable. The L. and N. W. R. has a much easier ruling gradient than the "G.N., yet the new "coupled " engines on the former only do 47 miles an hour, against 51 by the "singles" on the latter, although the former have larger tractive force on s more level line. IRISH AND SCOTCH MAILS. [15272.1-I SEE Willesden," in letter 15207 meations that the Irish mail is much longer than the Scotch. The up day mail consists of 7 coaches; down day mail of 10 or 11 (Irish and Scotch); the up night Irish of 7; the down night Irish of 9 or 10; up limited, 12; down 8.50 ex Euston, 12 or 13. The up day Irish has single 7ft. 6in. throughout; the down, coupled throughout. The up night Irish has single 7ft 6in. throughout; the down, single 7ft. 6in. throughout. So "Willesden" will see that the lightest trains are run by the single engines, not bat that the single engines could work the trains equaily as well as they used to when the trains were quite as heavy. As to stops, the up night Irish stops 4 times between Holyhead and Euston; the down, 3 times; the up day mail, 6 times; the down, 5 times, This is in 263 miles. The Scotch night 8.50 p.m. ex Euston stops 6 times from Carlisle to Euston (2991 miles); the up night stops 5 times. All Precedent class engines work this train. One thing. time is very seldom made up with Irish mail. The Irish is comparatively slow as regards the Scotch. 1151 Total heating surface... Weight of engine roadworthy, 48 tons. The advent of these engines does not seem to have been hailed with satisfaction by some parties who complain of the weight, but the accounts of the way they take trains up the Oldham banks are very satisfactory. The engines run from Manchester to Oldham. Bolton, &c., also between Leeds, Castleford, and Doncaster. With regard to the new goods engines the cylinder and boiler power is exactly the same as in the tank engines, but the coupled wheels are 4ft. 6in. in diameter, and the weight is 36 tons roadworthy I append a list of the East Lancashire goods engines as it may be useful. It is taken from the L. and Y. time-book, and is presumably correct. 1st class: 612, 613, 616, 648, then 700 to 718 inclusive, but omitting 713, 743, 744, 745, 746. 3rd class: 655, 656, 657, 658, 667, 668, 669, 670. 671, 674, 675, 691. 4th class: 604, 606, 613, 659, 660, 661, 662, 663. 661, 672, 678, 679, and from 681 to 699, omitting 691. December 25th. L. L. LOCOMOTIVE CONSTRUCTION. [15274.]-I SEE that "Technical" (letter 15236 doubts my being "a practical man." I think it would have been far better to have left "personal observations" which have nothing to do with the |