DEFINITIONS. (Continued from p. 221). [15106.]-THE differential calculus investigates the relation that exists between variable quantities, and measures the rate of their variation. The quantities considered in differential calculus are either constant or variable. A constant quantity retains the same value irrespective of the changes in other quantities. In the expression a + bv ev2, a, b, and c are constant quantities, and v is the variable. A variable quantity is one that is susceptible of a series of different values, and may vary continuously or discontinously. It varies continuously when in passing from one value to another it passes through all the intermediate values, and discontinuously when in passing from one value to another it does not pass through the intermediate values. When two quantities are connected by such a relation, so that if one of the quantities be allowed to vary the other varies also, then each of these quantities is termed a function of the other. A function is either algebraical or transcendental. Thus (a + bv + cv2)}, a®, (b + cv)", log. v, and cos. (c+v) are functions of v. The algebraical functions involve the ordinary algebraical operations, such as addition, subtraction, multiplication, division, involution or evolution, and the transcendental functions are trigonometrical, logarithmic, exponental, or special. The increment or difference of a variable quantity values in passing from the one to the other. The first letters of the alphabet are taken to represent constant quantities, while the last letters are taken to represent variable quantities. is the amount of difference or change between two We shall take v to represent the independent variable, and the related or dependent variable. We shall represent the increment or difference between any two values of the independent variable v by i, and any function of the variable by f. Let r = dr fv, then _ f (v + i) — fv = the differential co dv i efficient. Let r = cv, then cv + ci - cv ci = c = the differential coefficient. Whear alone occurs on one side of the equation, and on the other side some expression involving only v, as in r = a + by + cv2, then r is an explicit func tion of v. But in the expression a v2 + 2bvr + cr2, is an implicit function of v. Hugh Clements. (To be continued.) VERY ELEMENTARY ANALYTICAL CHEMISTRY. [15107.)—IF ́all the readers of the ENGLISH MECHANIC possessed that profound knowledge of analytical chemistry with which second-stage students are credited by Wm. John Grey, my very elementary" papers on this subject would certainly be of little use; but as there are but few of us whose scientific attainments are of such a high order, I venture to overlook Mr. Grey's protest, and continue my letters. Their object is to supply a want apparently felt by many readers, by furnishing them with the information in a compact form to which reference may be made at any time, and so save them the trouble of repeatedly asking and half a dozen correspondents of answering the same questions. Although in these first papers I am going over ground tolerably familiar to practical chemists, I hope to be able to give something new, not only to general readers, but also to the happy possessors of second-class science certificates, whose education after all, in the way of test-tabe shaking, may have been somewhat neglected. Mr. Grey suggests that I should copy from Valentin, but I am afraid that the following of this advice would give rise to complaints better grounded than his own protest. I have only glanced at the book referred to, but remember reading over a list of minerals, rejoicing in such names as Di Cuprotri, plumbotetrarseno, orthosulphantimonite, or something to that effect, surzounded by a string of Frankland's spider-legged formule, strongly resembling a choice collection of impaled daddy-long-legs in an entomological cabinet. Ciar Vohr. ["Collegian," ," "Elton Board," and "R. G. N." write, each expressing a wish that "Ciar Vohr " will continue his papers. The last-mentioned correspondent saya, "No reader of the E. M.' values the services rendered by Mr. Grey more than he does, but he disagrees with his latest letter so far as to think that Car Vohr's' contributions may and will be of very great use to less advanced students, who after all have claims on the consideration of the Editor and his more advanced con tributors."] PIPETTE. ours." [15108.1-I HAVE constructed a very useful give dimensions. Fig. 1, A, about 5in. of glass tube, pipette; it may be of service to some of in diameter; B, 9in. indiarubber tube, fin. diameter; and lin., by in. wide, by in. thick. Indiarubber CCC, three strips of deal in lengths of 12in., 9in., tube placed over glass about in., the other end turned up an inch or so, and fastened to bottom strip with thread, also bound at other parts marked thumb will cause the vacuum desired. With it I D; a slight pressure on the strips with finger and am enabled to capture small game from collecting bottles, &c., with great ease. 1. Compounds of arsenic are divided into two classes, arsenious and arsenic, which differ consider ably in their reactions. Arsenious salts are changed into arsenic by nitric, hypochlorous, and chromic acids, or other oxidising agents. Arsenic salts are converted into arsenious by boiling with hydro chloric, sulphurous, or phosphorous acid, and reducing agents generally. 2. Most compound of arsenic when heated on charcoal in the inner flame emit a strong garlic or, as it is called, aliaceous odour. 3. If heated in a closed tube with reducing agents -such as charcoal, NagCO3, or KCN-a shining brownish-black ring of metallic arsenic will be obtained. 4. The metal if heated with access of air, as in a bent tube open at both ends, yields a sublimate of minute glistening crystals of arsenious oxide (As2O3), soluble in boiling water. 5. Reinsch's test. On boiling a solution containing arsenic with a piece of bright copper-foil and HCl a coating of arsenide is deposited upon the copper, giving a sublimate of A203, on being dried and treated as in 4. 6. Marsh's test depends upon the fact that if hydrogen be generated in a solution containing arsenic a gaseous compound is formed, called arseniuretted hydrogen (AsH3), which if dried and led through a hard glass tube, heated at some point by a Bunsen burner, a dark ring of metallic arsenic is formed, which may be tested as before. 6a. This gas is also evolved when zinc and potassic hydrate are boiled together in presence of arsenic. 7. Arsenioretted hydrogen burns with a greyishblue flame, depositing metallic arsenic upon any cold body, such as the lid of a porcelain crucible, held in it. These stains are readily soluble in a solution of bleaching powder, and will be further considered in treating of the differences between the reactions of arsenic and antimony. 8. Hoffmann's test. If arseniuretted hydrogen be passed into a solution of argentic nitrate, metallic silver will be precipitated, and arsenious acid pass into solution-As H3 + 6AgNO3 + 3H2O = AsH303 argenious acid in this solution, filter, add a few + 6Ag + 6HNO3 To prove the presence of drops more AgNO3, and carefully neutralise the free HNO3 with NH,HO, when a canary yellow precipitate of argentic arsenite will be obtained. Arsenious solutions give the following reactions: 9. HCl + HS. Light yellow flocculent precipitate of AS3. Soluble in ammonia, ammonic carbonate, caustic alkalies, and alkaline sulphides, from which solutions it is precipitated by the addition of excess of HCl. 10. AgNO3 and AmHO, or, better, ammonic nitrate of silver, gives a lemon-yellow precipitate in neutral solutions. Easily soluble in HNO3 or AmHO. To prepare the ammonic nitrate solution add NHHO to AgNO3 in quantity rather insufficient to redissolve the precipitate first formed, and filter. 11. CuSO, and Am HO, or better ammonic sulphate of copper, gives a bright green precipitate (Scheele's green). Soluble in acids and ammonia, 12. Febling's solution gives on boiling a precipitate of red oxide of copper (Cu2O). acetate emits the exceedingly disagreeable odour of cacodyl-one of the arsenic derivatives of methyl. dissolving metallic arsenic in nitric acid or hypoArsenic solutions, such as may be obtained by chlorite, give with: 13. Arsenious oxide when warmed with sodic 14. AgNO3. Reddish brown precipitate. Soluble in HNO3 and NH4нO. cipitate. Soluble as in 14. 15. CuSO4 and AmHO. Pale bluish-white pre16. Magnesia mixture. White crystalline precipitate of ammonia-magnesium arsenate-As Mg (NH4)O4 + 6Ag. This reagent is prepared by adding excess of ammonic chloride and ammonia to a solution of Epsom salts. Yellow precipitate, Insoluble in acids, excess of an arsenic 17. Ammonic molybdate. appearing only on boiling. soluble in AmHO, and also in solution. The last two reactions are very similar to those of phosphoric acid. Antimony. 1. Solid compounds of antimony, when fused on charcoal with dry Na2CO3 or KCN, yield a brittle globule of the metal, while a thick white fume is given off, and the charcoal covered with a white deposit of oxide. The flame is also coloured pale blue. If the heat be continued for some time the metallic bead will be completely dissipated. 2. The antimony globule is converted by HNO3 into a white oxide, soluble in boiling tartaric acid or solution of cream of tartar. It is insoluble in HCl, but dissolves easily on the addition of a little HNO3, forming a solution of the trichloride (SbCl3), decomposed by water, giving a precipitate soluble in hydric chloride or tartrate. 3. Reinsch's test. Copper precipitates antimony on boiling in the form of a bright metallic film, soluble in permanganate of potash, the solution giving a reddish precipitate with HS. If oxidised and sublimed in a tube open at both ends the sublimate will be found quite insoluble in boiling water. 4. Marsh's test. Nascent hydrogen evolved from zinc and HCl combines with antimony to form antimoniuretted hydrogen (SbH3). If the conducting tube be heated at a point, as in the case of arsenic, a metallic deposit will be obtained, which may be treated with aqua regia and H2S, or moistened with HNO3, evaporated very gently, and touched with a drop of ammonic nitrate of silver, when a black spot will be produced. 5. If the tube be drawn out to a point, and the gas lit, a porcelain crucible lid held in the flame will cause a deposit of antimony, which may be tested as mentioned in 4. It is unchanged by bypochlorite. 6. Hoffmann's test. Antimoniuretted hydrogen led into AgNO3 solution gives a precipitate of argentic antimonide (SbAg3). If this precipitate is washed. boiled with tartaric acid, filtered, acidised with HCl, and H2S added, an orange-red precipitate will be obtained. 7. Antimoniuretted hydrogen is never evolved when zinc or aluminium is heated with potash. So differing from arsenic. An acid solution of antimonious chloride gives the following reactions: 8. H.S. Orange red precipitate of sulphide (Sb S3) easily soluble in fixed caustic alkali, and all alkaline sulphides. Almost insoluble in ammonic carbonate. 9. KHO. Precipitate of trioxide soluble in large excess. 10. Chloride of gold (AuC3) gives a yellow precipitate of metallic gold, and when there is no great excess of HCl. SO, is precipitated as a white powder. 11. Zinc, iron, and tin precipitate antimony as a black powder. 12. If a piece of platinum be placed in the sola tion, and a bit of zinc dropped upon it, a black deposit of antimony comes down on the platinum. 13. Solution of She03 in KHO gives a deep black precipitate with AgNO3, insoluble in AmHO. Tin. 1. All compounds of tin reduced on charcoal with metal. Soluble in strong warm HCl, the solu NaCO3 and KCN, yield white malleable beads of tion giving a white or grey precipitate with mercuric chloride. If one of the globules be fused into a borax bead coloured blue by copper, it will become reddish and opaque. HÑO, converts tin into insoluble stannic oxide (SnO2). 2. Stannous solutions are made by dissolving the metal or oxide (SnO) in acids. Then chloride (tin salt) is most frequently met with. They are de composed by water, except in presence of a large excess of free acid, and rapidly oxidise on exposure to air. They also act as powerful reducing agents. 3. HS. Brownish black precipitate soluble in ammonic sulphide containing excess of sulphur, from which solution it is precipitated by HCl as yellow stannic sulphide (SbS). 4. HgCl. White precipitate of HgCl turning grey on addition of excess of stannous salt, owing to the reduction of metallic mercury. REPLIES TO QUERIES. In their answers, Correspondents are respectfully requested to mention, in each instance, the title and number the of query asked. house pro each for rent, which, added to their payment of ground rent, &c., would bring them about level with their fellow-members. At the end of 2nd year 13 cottages could be built; at end of 3rd, 15; 4th, 17; 5th, 18; 6th, 20; making 105. The remaining 15 could be built during the next 8 months; so that by this "saving" society each member could purchase a house for 63. per week savings in 63 years, value £210, the actual cost of each house being only [33617.]-Rat Hunting a Rabbit.-Being a new subscriber I cannot go back to the original question, £100 to each member, the remainder being the result but I know for a fact that some old rats do hunt of rent, co-operation, and accumulated interest at down rabbits same as the weazles. For the informa-5 per cent. As loan societies make their estimates tion of your readers I will relate to you what occurred at 14 years, it is just that I should so estimate this to me some years ago. I went to see a sow and litter principle, which can be done by simply repeating of young pigs, when to my great astonishment I the society a second 63 years. Now, it must be found a very large grey tailless rat sucking the sow duce 63. per week net rental. which each member admitted that such a cottage as named would prothe same as the young ones. I at once stopped the could put into the society in addition to his 63. per rat-holes, and watched the rat sucking for some time. As I was in a hurry I could not wait to allow week savings; so that he would be able to purchase him to be satisfied, so I touched him with the toe of or build 2 houses in the second period, making him my boot, which caused him to run straight to the in all 3 houses at £210 in 134 years for 6s. per week wall which he struck with his nose, he then turned savings. This calculation contains 4 per cent. for towards where the hole was, and finding it stopped working expenses. Thus we may see that the saving turned round and round. I then gave it a slight principle with co-operation is about three times the kick, which caused it to turn on me with a most value of the borrowing. It is not my wish to be dreadful squeal. I got out of the stye as quick as I supposed to imply that the present " are not a could, the rat following me. When out in the open perty, loan, and investment societies I was able to kill it, and found that it had not a benefit, in their way, to the working classes-I believe that they are, just as "labour loan societies" single tooth in its head. I believe it was also per-e, but the benefit they impart is not in the facilities they afford for persons to borrow, but in the inducement they offer for working people to systematically save. As a matter of direct profit, those who borrow must pay those who save, and in addition must pay the working expenses; so that there can be no direct profit in a mere borrow and lend" society. In a co-operative building society there would be the direct profits of co-operation and interest on money saved. In short, for so-called "building societies" to be made really profitable to the community which they undertake to benefit, they require to have infused into their board of management a little more really useful mechanical skill and artisanship, and a little less of the commercial big book and blotting-paper "red tapery." In regard to Justitia's" reply to my note. I see little use in attempting to convince one so obdurate in misstatements. I can see no reason, however, for the boldness he displays in flatly contradicting No need exists for donning the lion's mane when my statement as to documents which I have seen. a gentleman who writes under a nom-de-plume charges another with falsehood. I shall, therefore, not trouble to point out to him that the reply in which he attacks me in a personality admits a principle which necessitates the existence of the documents which I have seen.-R. B. CAVE. To recapitulate:-Reinsch's and Marsh's tests most conclusive tests for tin are the characteristic (To be continued.) LINES of underground telegraph wires are now in successful operation throughout the whole distance -1,210 kilometres-between Strasburg and Kiel. Revelations of Cotton-warp Sizing.-An interesting case to manufacturers, merchants, and the public was investigated at the Rochdale county court, before Mr. Crompton Hutton, on Thursday, last week. The plaintiffs were Matthew Stuttard and Brothers, waro sizers, Whitworth, and the defendant Charles Grindrod, cotton manufacturer, the amount in dispute being for £6 49. 91., the price charged for sizing 27 warps. The defendant put in a set-off for £20 53. for loss sustained from the way the warps were sized. In answer to the judge, the plaintiff said that if the court were cleared he would tell what the sizing consisted of. The judge said he would have to tell them when all were present. The witness then said that the size consisted of flour, china clay, Epsom salts, chlorate of zinc, chlorate of magnesia, and glue. In answer to Mr. H. Brierley, who appeared for the defendant, witness said that about 70 or 80 per cent of the size was put into the cotton. He did not think there was as much as 120 per cent. in Grindrod's warps. A sample of the material was produced in court, and the stench was disagreeable. The judge asked what was the utmost amount of sizing he ever put in. Witness replied about 130 per cent. The judge next asked, from his personal experience, what had he known put in. Witness replied 200 per cent. of size, but not at his works. He had been in the trade 20 years, and in commencing only put 5 per cent. into the warps, and the size then consisted solely of flour, but now they had to add chemicals to get the weight up, as manufacturers asked them for more weight. The judge remarked that this was a clue to the depression in the cotton trade, because in time the purchaser would find out the quality of the material. Mr. Brierley replied that he believed that it was the real cause of the depression of trade in India, for he had been so informed by some of his relatives who were there. The judge said it was of importance that this fact should be extensively known. The judge decided that the defendants were entitled to recover the difference between the £20 and the £6 48. 9d. and costs. Experiments with the Jablochkoff Candles. -M. Petronchevsky is reported in the Chemical News as having made some experimental measurements with the Jablochkoff candle, with the view of estimating its light giving power in several forms. For the purpose of his trials he employed (1) candles in which the carbons were divided by gypsum, and (2) candles with carbons divided by kaolin; using the photometer of Bunsen for his measurements. He found the following results :— (1) CANDLES WITH GYPSUM. Intensity of light in No. of revolutions of stearine candles. machine per minute. 931 931 1200 1350 2500 1224 1200 The machine employed was a small Gramme. The experiments show, therefore, that gypsum as a divider of the carbons gives the best results as to luminous intensity. The author qualifies this statement, bowever, by saying that the light with kaolin has more steadiness and is more agreeable to the eye, [33717.]-Electro-Plating.-Through an oversight I omitted to state in my last reply to this query that the second patent alluded to referred merely to the preparation of the articles, previous to immersion in the bath.-C. J. LEAPER. [33925.]-Building Societies.-The dispute on this subject appears to be somewhat similar to the celebrated argument as to the golden and silver sides of the shield, in which both disputants were right. It may be very true, as "E. W. A." and others state, that the £16 which, in the instance quoted, has to be paid beyond the £27 rent would, if invested at compound interest, purchase the house at the end of the 14 years, in its then deteriorated state: but let me ask these writers one simple question: Where is the man of limited means (and building societies are for such) to get a safe investment that will pay him 5 per cent. on such possess the moral courage to put by money, volunAgain, how few are they who tarily, in the face of the numerous demands sure to arise during such a lengthened period-some unfortunately unavoidable! These considerations lead me to believe that the matter resolves itself, in most cases, into a question of getting a house by this means or doing without one, the rent still going for mere occupation. On the other hand, payments to a building society are, like insurance premiums, of the quasi obligatory class, to meet which every effort will be made rather than their benefits should be lost.-J. H. small amounts ? ་་ misapprehension exists in the mind of R. B. Cave on [33925.]-Building Societies. "E. W. A." (U.Q.).-There is no solution by which you can do [34169.]-Depositing Lead and Silver on Iron this. The only plan is to deposit by the electro [34212.]-Pumping Water.-The first question is answered by the following rule, taken from the Diameter of pipe in inches, number of avoirdu. Mechanic's Calculator," by Wm. Grier, C.E.:pois pounds contained in 3ft. length of the pipe. The second is answered as follows:-As 40: 45 71:: 9,350 to the result. I fail to see where 2021b. is the average weight of 1 fathom.-A. L. K, [34271.]-Du Bois Raymond Coil.-Would "Medical Rover" kindly tell me how many yards of wire are on each of his coils, or what is their weight; also what kind of paraffin is the best to use for varnishing the wire ?-PERSEVERANCE. [34272.]-Model of Ship's Stern.-If "Test Valley" is in London, he should go to South Ken sington, where he could measure a number of models. -RUFUS. [34282 and 34283.]-Launch Engine and Link Motion. This querist should surely say what it is he wishes to know. Link motion has been illustrated over and over again; but the best thing he can do is to see it at some shop, such as Bateman's.-RUFUS. [34287.]-Oil Tester.-Try Bailey's.-S. M. [31296]-Physics of the Ocean.-I have to thank Mr. Brown for taking the trouble to reply to my hasty remarks on his answer to the above query. On farther consideration I agree with him that the cannon-ball would fall with an accelerated velocity in the depths of the sea with which we are acquainted; but I still hold that, in theory, a point might be reached at which the cannon-ball would come to rest. At what point in its descent would the change from accelerated to retarded motion take place? The statement regarding the floating substances I have certainly seen made somewhere, although I am sorry I cannot refer Mr. Brown to any particular authority.-J. B. W. OLIVER. [34297.]-Lathe Castings.-The reply to this question is certainly yes.-PEDRO. [31299.]-Harmonium.- No objection, except that it would be more costly and less convenient. W. H. [34326.]-Snails.-I have found fine dry forge dust shaken lightly at bottom of wall a very good trap for snails and slugs. It adheres to them, and prevents them getting away.-JOHNSTON. [34340.]-Domestic Steam Engine.-I think the steam engine referred to by S. Townsend was manufactured by a plumber and gasfitter named McComas, who resides in Talbot-street, Dublin. I cannot give any further information, as I know nothing what ever about engines.-JOHNSTON. $4359]-Packing of Throttle Valve. If "Enow" will ent his indiarubber a trifle thinner, and lap round with flax, so that he keeps the india rubber from the spindle and stuffing box, he will find it will not stick, but work free, and last for a long time. I packed one on June last, and the engine has been at work every day with the exception of shed days, and there is every prospect of it standing for a long time to come.-JOSEPH GREEN. [34375.]-Emphysema of the Lungs.-" An Eight Years' Subscriber" had better advertise bis address in the usual way. The solvent is a proprietary preparation, in the sale of which I have no interest whatever, but am willing to impart what I know without fee or reward.-Z. [34423.]-Sciatica.-If your disease be inflammation of the hip joint, as mine was, the only cure is absolute rest, aided by fomentations and blisters. This is best secured in an hospital. My medical attendant recommended me to a local infirmary where he was visiting surgeon. My leg was put in a splint. Don't be taken out of the bed for the purpose of having it made. I found that by being moved to get an easy bed I injured my leg, and so desisted from the practice altogether, which proved beneficial. After being in bed some time-the doctor says how long-my leg was put into a stiff bandage, and I was allowed to move about on crutches, and now I am able to move about with only a stick. From what you say you are not nearly so bad as I was, as described above. You are as I was before I thought seriously about my complaint. If I had had proper treatment in the early stages of the disease, the doctor said I should not have required the use of crutches. Therefore endeavour to get the proper treatment-rest-at once. If inflammation goes on unchecked in the joint it results in abscess on the joint or diseased hip joint, which is very difficult to care in aduits. I have spoken plainly that you may not procrastinate; but I have only told you what should have been thankful for when I was as you are.-L. B. D. (34431.)-Cleansing Lather.-I am exceedingly sorry that I could not find an opportunity of replying earlier to the above queries. Water of borax is Dothing more nor less than a saturated solution of the biforate of sola in the cold. The formula that "Deislus" mentioned is perfectly correct. Shampoo lather is made by dissolving an ounce of the sub-carbonate of potash in an imperial quart of water, but if this is not sufficient for his purpose he can easily determine the quantity by experiment. D. STRATHEARN, Med. Stud. a half shovelfuls to every barrowful. Please say how you have succeeded, as I never tried it with pipe clay, but have succeeded very well with very fine blue clay. I do not know any glaze but the salt glaze.-JOHNSTON. [31161.]-Colouring Gold.-The ingredients are not mentioned for colouring gold. What does "Os" mean by "pickled ?" Will he be so kind as to give a full list of the ingredients that are to be put into the crucible, with the amount in each case ? -PEDRILLO. [31473.]-Separation of Antimony and Tin.I am much obliged to Ciar Vohr" for his answer to this query, and shall be very glad if he will furnish details of the method of separation as given in Crookes' "Select Methods," which I presume professes to be a quantitative method. I believe the quantitative separation of these two metals is always attended with difficulty. I believe Thorpe generally selects very accurate methods. Is not this also "Ciar Vohr's" opinion ?-GUY LUSSAC. [34477.)-Rats-Coal or Archangel tar poured If a few live rats were caught, and well painted with and brushed round the holes will scare all rats away. the tar, then let into the holes, I can safely say no rats will come through them for a long time. The rat is a very clean animal about his person.JOHNSTON. [31484.J-Exercises or Gymnastics for Ladies, -An excellent book on this subject is "Calisthenics and Drilling Simplified," by D. Cunningham, pub. lished by Haughton and Co., 10, Paternoster-row, E.C.-R. A. P. DAVISON. [34514.] Yellow Spectacles. To W. J. LANCASTER.-Accept my best thanks for your promised advice. I was led to ask the question from hearing that a London docter had strongly advocated their use, on the ground that yellow glass transmitted light, but stopped the actinic and heat-giving rays, which to an outsider seemed satisfactory reasoning, having in mind that blue glasses were the reverse of cool. However, to answer your questions. With the right eye at less than 12 inches the letters present a broken appearance, improving up to 18 inches; cannot read with the left eye unaided at any distance, and but badly at 18 inches with a strong magnifier; it is therefore generally kept closed when reading. As to persistence, an example may be best. On examining a map for some minutes, and then resuming my reading the principal lines of the map (rivers, roads, &c.) are seen faintly on the page, shifting about as the eye moves. But a still stronger proof is, that on awakening at night, and looking up at the ceiling faint lines of type are visible for a few seconds. I should perhaps add that I am a great reader having, owing to infirmity, scarcely any other resource. Can glasses be got by asking for 36in Some time ago, in purchasing a pair for a friend I was told to get No. 13, without any mention of inches.-SIXTY-FIVE. [31525.1-Blood Poison.-I have suffered from the same kind of ulceration. The cause was not, I feel sure, a bad atmosphere or a defective sewerage. With a return to a better state of health consequent on taking more exercise and a greater quantity of nourishment, the ulceration has disappeared. Wash. ing the teeh frequently, especially after meals, has I think been beneficial. I would recommend also as a mouth-wash, "Sanitas" (toilet quality), sold by most chemists, price 1s. a bottle.-W. [31536.]-Adansonian Fibre.-This bark is an excellent material for paper-making, but the supply is limited and prices high, so that little is used. "Adansonia digitalis" is from the Baobab tree.JIB. [34541.]-Spanish Pyrites.-1. It is quite possible to burn Spanish pyrites, leaving not more than 3 per cent. of sulphur in the cinders; 2. I charge each furnace with 7ewt. once in 24 boars, and after 16 years practical experience find it the best system; 3. And cause each furnace to be stirred or pokered once every 4 hours.-VITRIOL. (34558.-Drilling.-Size of entering holes for Whitworth standard screw taps :Size of hole before tapping. in. 17 43 3 7 31 17 15 117 1 214 -LANCASHIRE FITTER. Finished size. in. 14 (34432]-Brickmaking without BurningThere is no difference in the manufacturing of this and bricks that are burned. They are used only for stadding between two apartments, instead of lath and plaster. They are as good as burned brick for this purpose. Clay with a large quantity of limestone in it, and which would not be worth crushing, is manufactured into unburned brick.-JOHNSTON, (34445.)-Steel.-"Sheffield" will find Dr. Percy's (the well-known lecturer on metallurgy) work on "Iron and Steel" by far the best and most comprehensive; the price, I believe, is 34s. If he refers to the last numbers of the Iron and Coal Trades Review, [34568.)-Sound Conducting Property of published at 7. Westminster Chambers, Victoria. Wood.-If "Joiner" wants to destroy the sound stret, be will see an advertisement of metallic in a partition place between the studs dry peat-put tangsten, the only source in Eagland where he can in the same as brick.-JOHNSTON. obtain it at a suitable price for commercial purposes. [34570.]-Indicator Diagram-As I don't feel -E. FITZGERALD. satisfied with the answers given to this query I beg [34483)-China Clay Crucibles.-Your clay to offer my own ideas. There appears to me to be a being too fine for such heavy articles you must make sudden leakage when the piston has arrived at that it porous with a little soil, or, better still, crush a point of its stroke represented by the top of the half-burned piece of the clay, and mix, say, one and loop-(N.B.-This is not the end of the stroke, as supposed by "R. E.")-but how this leakage occurs is, I take it, almost impossible to conjecture without an examination of the cylinder opened out. Now, "A. L. K." should have sent a diagram from the other end, as the two diagrams will often verify an opinion, which can only be a guess from the one diagram only. However, looking at the diagram before na it seems to me that a sudden fall in pressure begins at the top of the loop, and continues until the bottom point of the loop is marked, or until the piston has arrived at the end of its stroke, at which point it begins to rise until the piston has arrived at a point exactly under the top point of the loop (where the sudden drop begins), when the pressure rises more rapidly. Now we will suppose that the piston passes the port; what would be the result? The compres sion would go on until the piston passed or opened the port, when the confined or compressed steam would rush past the piston into the other end of the cylinder, and a drop in the pressure would continue until the valve was opened to steam, when part of the steam would pass to the back of the piston, and the pressure would rise perhaps in the other part pressure or admission line would rise in the usual until the piston again closed the port, when the way; and this appears to me to agree with the pressures as indicated by the loop. Of course if this is a correct solution, the pressure caused by the steam escaping past the piston ought to show itself at the exhaust corner of the other diagram. Perhaps "A. L. K." could send it. I should be pleased if he could.-ARQUES. [34571.]-Tinning Saucepans.-You will find the tinning of cast-iron saucepans too expensive. Copper ones may be done as follows:-Scour the part to be done until quite bright with a soda soln. tion, with scales from the anvil in it. The soda should be put in boiling water, and made strong. When bright rinse in cold water, and before the saucepan is dry rub it well with sal-ammoniac. Block tin is the best for a good job. Melt it in a ladle, and pour it in when you have got the saucepan to a proper heat to take it. You will have to use your own judgment about the heat, and will find it an advantage to have a soldering iron to assist and run the metal. Begin with the bottom first, and work up the handle; do not try to do too much at once. Finish off at the front, so that the spare metal can be put back in the ladle. If you find any place missed put more sal-ammoniac on that part. wiping out; when completely covered and cold polish As you are proceeding with the tinning use tow for with fine silver sand. You may not expect to suc ceed at the first trial.-TINMAN. [34574.]-Breaking Roll.-Get a few charges of gun-cotton to break it; it is a simple process. Get your roll solid on the ground, put a charge on top surface of roll near the centre, place a detonator and a safe length of fuse, and cover all with a flat cake of clay, leaving a part of the fuse protruding through the clay to fire it. I have seen chilled rolls of 28" diameter broken into pieces of balf-hundredweight easily in this manner. I would advise you to get a person that understands the use of gun. cotton to do it. If that is not available prop your roll up both ends about a foot clear of the ground. light a good coke fire under and around it, get it near the cupola tuyere, and put the blast on until it is white hot underneath, a few blows from a heavy sledge-hammer will then break it. I have found by experience that gun-cotton is the cheapest method. -T. FRANCIS. solution of alum, when the dye will take.[31576.J-Dyeing Grass.-Wash the grass in a JOHNSTON. [31586.]-Melting Copper.-Get a plumbago crucible; you can get them any size from 4oz. upwards; they are the best I know of. I have one now that has melted 24 times, and to all appearances will last another 24 melts.-T. FRANCIS. nal Venice, dates from 421, the succession of the [34587.]-Venice.-The town of Rialto, the origi Doges from 697. The government was at first in the hands of the people; but as the wealth of the state increased so grew the power of the nobles. Doges acquired and abused the sovereignty, and for centuries they and the nobles struggled to obtain the mastery. The aristocracy prevailed, and from that time jealously confined the government within their own body. All public spirit gradually disap peared, and the republic fell, at the summons of Napoleon without a struggle. If "Thane" can procure Sismondi's "History of Italian Republics," Evelyn's Travels in Venice," Condor's "Italy," or Eustace's Classical Tour," he will find every information.-AN OLD SHOEMAKER. [34593.]-Boring Bit.-If "N." will get a brass countersink, cut off the point, and re-cnt it to the shape wanted, he will find it the tool he wants.STOCK TURNER. (34504]-To Preserve Eel Nets.-Catechu is the material used by fishermen to preserve their pets. A strong solution is made in boiling water, and the nets are well soaked in it while hot. Sails are also tanned in the same way. Oak bark is sometimes added to the solution, where a large quantity is required. I have preserved eel skins by simply dry. ing, and beating afterwards with a mallet to soften them. I think they might be tanned in the catechu solution.—WAR. (34594]-To Preserve Eel Nets.-Tan them either with oak bark or catch. A few days or less will be sufficient.-H. R. PROCTOR, [94595.]-Motive Power for Lathe.-Any high pressure steam-engine can be driven with air, and the ordinary gauge will do. The air-condenser will get hot if not cooled with water. Will not the plan be somewkat costly ?-H. R. PROCTOR. [34600.]-Limelight. An ordinary Herepath blowpipe with small jet, fed with oxygen, and directed on a lump of lime, will give a brilliant light; or a common blowpipe directed through a Bunsen lamp, with the air holes closed, might do for a lecture experiment.-H. R. PROCTOR. [34604.]-Phosphorescent Centipedes. The Scolopendra electrica (phosphorescent centipede) is not uncommon, but is seldom seen, as it rarely leaves its holes by night. It may often be found in the débris collected in hollow trees. I should be glad to know if the phosphorescent matter, a trail of which is left by this myriapod, has been microscopically examined.-OTTER. [34605.]-Draught of Bicycle.-To give "V." anything like a correct idea of what he wants to know could only be done by a series of experiments, and it would also depend upon "V.'s" experience on a bicycle, as a good rider can propel a bicycle 8 miles per hour with less power than a learner. The weight, kind of bearings, and rake of machine would have to be considered; it would have to be known what "V.'s" ideas of roads were, because what into use until 4 centuries after clocks were first [34613]-Watch Finishing.-Prepare crocus or [34614.] Bunsen Battery.-This does not happen so long as the batteries are kept in use, and the porous cells wet. When you put the batteries away you must allow the cells to soak for several hours in water, changed every half hour, before letting them get dry. This is the only way of overcoming the difficulty.-GLENNAQUOICH. [34619.]-Geneva Screw-head Tool.-If "Ex. would be called a good road here I suppose might be perimenter" will go to any watchmaker's tool-shop set down as an indifferent one by a south country he will be shown this tool without objection, and bicyclist. Under such circumstances" V.'s" question cannot be answered without "V.," his bicycle, can see much better than by a diagram if it will answer. I cannot understand how a respectable and foot-lathe were present. The draughts of jobbing shop anywhere should be without one, either bicycles differ as much as the draughts of ships.-Geneva or English; from the latter Experimenter" will get a sufficient idea of the suitability of the former, if bis object be an extra-trade one.LIVERPOOL FINISHER. 50in. KEEN. [34607.]-Boring Holes Endways of Grain.I have made bits for a mortising machine (boring) like 2 pin bits-back of one overlying the other, one put in a chuck. If "Inquirer" can get speed and power they will bore any way of the grain. I have a small one he could see if he will advertise his address and pay the postage back again; and the -T. P. 21 7:048 8.273 11.8 44° 18 3 7:878 11.1 100 000 45° 21 6.827 7:477 10.9 18.3 6.830 8:003 10.8 89.250 12.096 82.625 46° 12:096 it. Brooke's "Natural Philosophy" requires a more B [34639.]-Theatrical Lightning.-The powder generally used for lightning effect, &c., is very finely powdered rosin blown through a tube; coming in contact with a light it produces the flash of blue colour. I know of no powder which produces the effect by being lighted with a taper.-T. P. lycopodium is used for this purpose, probably a [34639.] Theatrical Lightning. Generally little magnesium powder with a thin piece of blue gelatine in front. Blue fire would burn too slowly, but could be burned in a vessel with a door, so that a number of flashes could be produced by opening and closing the door.-W. J. LANCASTER. [31610.]-Electric Lighting.-To MR. LANCAS TER.-You would not require an induction coil to produce the light; the cells should all be connected in one line, so that the elements are continuous. The best size carbon plates I have found to be about 4in. x 24in., the zinc being the same size, and the two plates about in. apart. I have during the last week devised an arrangement which keeps the bichromate cells in action for 4 or 5 hours, and I have also devised a lamp which gives a continuous light, and will produce such a light from 12 bichromate cells, lasting for 5 hours. I should have sent all sketches, &c., this week, but I am not quite ready, having been reducing the lamp to its smallest limits. I have done away with regulators in any form; the lamp is self-feeding, and will burn any length of time, in proportion of course to consumption and steam or hand.-LANCASHIRE FITTER. supply. I hope to send all particulars to our next number. At present the lamp could be made well The work is composed of marble. The huge blocks elements costing perhaps 9s. per dozen pairs, and the [34625.]-Plymouth Breakwater Marble--for a guinea; the cells are of course very cheap, the used in its construction weigh from one to ten tons cost of chemicals is very little more, especially as I each. The quarries from which these were procured now use them. Gas carbon is the best material for are situated at Overton, on the eastern shore of Cat; experimental work, but I hope to add infusible water; they lie under a surface of about 25 acres, and electrodes to my lamp, and if I can do all I hope to thousand pounds. These quarries consist of one vast be covered either with indiarubber or guttapercha. were purchased from the Duke of Bedford for ten do I will communicate the results. The wires should mass of compact close-grained marble, many speci- the former preferred, but for a small light this is of mens of which are beautifully variegated. The first block was sunk on the 12th of August, 1812, and on no moment.-W. J. LANCASTER. the 31st of March, 1813, the breakwater made its [34644.] Photography. There are many first appearance above the surface of the Sound at methods for the production of purple prints. In the low water spring tide; at the conclusion of the year first place there is a paper manufactured of that 1816 upwards of one million tons had been deposited. colour which looks very pretty, more especially in Eddystone lighthouse consists of Portland stone vignettes. The next is the Bath, of which there incased in granite.-AN OLD SHOEMAKER. are many formulas. The one that is generally used by "card" photographers is as follows:-Formula, [34625.]-Plymouth Breakwater Marble.-chloride of gold, 15 grains; acetate of soda, 1 ounce; The brown marble ink bottle which "Murano" pos- water, 40 ounces. You can make up the whole of sesses is made of what is commonly known as Devon this with profit, as it keeps well, and is likewise a shire marble. This is merely limestone, which admits very good bath indeed, as you can procure any tone of a very fine polish, and I have seen it in nearly all you like. Warm it in cold weather-it works quicker. colours, from a pale blue to the most delicate salmon I know of no practical camera for what you mention. colour. It is procured from the Preston quarries, I heard of one the other day, but it had so many near Plymouth, which furnished the whole of the drawbacks and flaws that the inventor and myself stone for the Plymouth breakwater. The Eddystone thought it a failure. The only handy way is to have lighthouse is built entirely of granite (Cornish), and a dark bag to change them in, put your head and I believe the lighthouse on the breakwater is also of arms in, and it can be rolled into very small com. granite.-ADYE DOUGLAS. pass. The dark slides are another good contrivance. PROFESSIONAL PHOTO. [34631.]-Varnishing Paper.-You have pro- [34610]-Old Clock.-If your clock was made, to fostering the spread of information, the collection [34656.] Engine Cylinder. Make feet 4 TOP of which has already cost so much, would be a wise brackets, loose, and mould in a 3-part box, as per expenditure. It would increase the scientific know. ledge of the people, give a greater interest in our museums, give an impetus to the study of the various branches of natural history-the educational value of which is so great-and do something to counteract the bad taste (and bad morality too) inculcated by the pernicious trash of the " penny dreadfuls" which we see so widely diffused and read. Induce a man to take up natural bistory or science-to have a "hobby"-and how his intellect is improved, his mind expanded-how much he sees which he never noticed before, and how he must look from Nature to Nature's God! Mentally compare the man who has throughout the year read our ENGLISH MECHANIC with one who has wasted his time in sensational garbage. What a difference! A better workman-how much more intellectual-knowing more. but also appreciating the littleness of his knowledge and how much he has to learn-a more reasonable being, a better citizen.-J. N.D., Tuxford. [34649.]-New Zealand Moon. - If "Stargazer" would stand himself upon his head next time the moon shines he would place himself in the relative position with the face of our satellite that the residents in New Zealand constantly maintain, and the vague resemblance of the moon's disc to the features of a man would transform themselves into a badly defined map of America.-GIMCRACK. [34650.]-Drawing the Corona.-I am surprised you did not at once refute the absurd argument of the lecturer. Look at a bright light, and you of course will see a number of radiating rays of light, but hold between the light and your eye an opaque body just obscuring the light, and "oh! where, and oh! where" have the rays gone? The disappearance of them cannot be put down to any alteration in the lamine of the crystalline lens, but in the fact that the source of illumination has been obscured. With special reference to the corona, you might have questioned him as to how the fact is to be explained that both drawings and photographs come out so nearly alike. Would he hold that a photo lens had a fibrillated structure? I suppose not. At the same time I have never yet been perfectly satisfied in my own mind with the corona, and I should be obliged if "F. R. A. S." would be good enough to give the information I now lack. When one holds a circular disc between the eye and a circular source of light-e g., an opal globe containing the electric light, it is found that a series of circular rings is produced of various colours; in fact a circular diffraction spectrum is seen, beginning with a red circle touching the dark disc, and passing through the other colours of the spectrum in the outer rings. These colours are only seen when the light is in focus on the retina, and are lost when the eye is adjusted to the disc. Now, do eclipse observers take this diffraction into account, and allow for it? This is my query then-Are astronomers well grounded in the appearance of diffraction spectrums, and do they allow for them during eclipses ?-W. J. LANCASTER. [34653.]-Telephones.-Have a single line wire connected between the two houses, and use the gas pipes for return wires. You may use galvanised wire-it will not require insulation. The right way to wind the wire on the magnet to make it suitable for a telephone is to wind it on the south pole in the same direction as the fingers of a clock or watch travel, and upon the other pole the opposite direction to the motion of the fingers. Connect the wires near the bend of the magnet, and the other ends to the binding screws, to be connected to the line wire. -W. J. LANCASTER. [34655.1-Lathe Saddle.-I should recommend using 2 half-nuts of gun-metal, and working them, sketch; then there will be no difficulty in getting pattern out of sand.-W. S. [34660.]-Hydraulic Rams.-" Country Bump. kin" gives but meagre particulars of the site where he proposes to fix a ram. The elevation as givenviz., 900 yards rising 1 in 3-would be 900ft., for which height a ram would not be suitable. This is probably an error, and if he will give it correctly. and measure the flow of water by observing how long it takes to fill a two or three gallon bucket, or further. Before choosing a ram it is necessary to by the following plan of gauging, I will advise him ascertain the quantity of water available for working it. This may, sometimes be done by catching the water in a bucket or measure of known capacity, and noting the time required to fill it. Generally, however, the only practicable mode is by causing the water to flow over a notch or weir, as represented in the above sketch. The weir most suitable for small streams is formed of a piece of in, deal (Fig. 1) of FIG.I FIG. 2 sufficient length to span the brook, having a V notch cut in its upper edge, the angle of which must be a right angle or 90°. A convenient depth of notch is 5in., which is large enough to allow the passage of 110 gallons per minute. The edge of the notch should be chamfered off, so as to leave a thickness of 1-16in. only in contact with the flowing water. The ends and bottom are also chamfered for convenience in fixing. A peg with a step cut on one side, as shown in the annexed sketch (Fig. 2), should also be provided, care being taken that the height from the step to the top of the peg is exactly the same as the vertical depth of the notch. A rule divided into inches and tenths completes the apparatus required. After choosing the site for the dam, with a sharp spade cut grooves in each bank, and press the board down firmly in the grooves, so as to entirely stop the water, pressing soft clay round if necessary. Now measure the height from the surface of the water to the top of the board at each end, and press down the highest end until it is quite level. When the rising water approaches the bottom of the notch, fix the peg into the bed of the brook at a distance of about 3ft. from the weir; and at the moment the water rises to the bottom of the notch, drive the peg down until the step is exactly level with the surface of the water, and therefore level with the notch. The water will now begin to flow through the notch, and will rise to a height that corresponds with the supply; so that by ascertaining the depth of water running over the notch, the quantity may be deduced. This required depth is now to be measured in inches and tenths, by putting the end of the rule on the step in the peg, and carefully noting the height of the surface of the water. The flow of gallons per minute, corresponding with the height, will be found in the following table, calculated for the purpose by the writer. To shorten the length of time required for the operation, it is advisable to stop the notch with clay while the water is rising, Care should be taken that the stream be damned up by the weir sufficiently to reduce it nearly to the condition of a still pond, and also that the water should have a clear fall from surface to surface not less in height than double the depth it runs over the notch. Where great accu racy is required, the weir should be adjusted by means of a spirit level, and the top of the peg made exactly level with the upper edge of the weir by means of the same instrument and a parallel straight edge. The weir may with advantage be faced with thin sheet iron, and the notch cut through it; that through the wood being made of larger dimensions, so as to reduce the friction of the water to a minimum. TABLE OF QUANTITIES OF WATER CORRESPONDING TO A GIVEN HEIGHT ABOVE THE BOTTOM OF THE NOTCH. Height in inches. 2. Quantity in gallons per minute. 10 76 [34660.]-Hydraulic Ram.-There must surely be an error in reply on page 233. 5 gallons per minute at a head of 6ft. is equal to 1 gallon at a head of 30ft. Can one gallon falling 30ft. raise another 40ft.? Rams are considered to utilise about 60 per cent. of the theoretical power.-J. BROWN, Belfast [34665.]-Varnishing Stephen's Stains.-I think the white and greasy look which "R. O." speaks of is either occasioned by his not having varnished the wood in a warm place or from his brush being damp. I have found this to be the case in using spirit varnish.-PICTOR. [34667.]-Endorsing Ink.-"Iron Horse" can make an endorsing ink of any colour with Judson's dyes and glycerine. His druggist will mix it for him.-PONTO. [34668.]-Electrotyping.-1. One wire should be insulated, not by covering, but simply at its supports to prevent leakage along walls, &c. 2. See reply 34691, as to thermo-electric batteries. 3. Rub the surface over in the plumbago; when first put in liquid, lead the current to the most difficult parts hollows, &c.-by a guttapercha-covered wire, with the point only exposed, and touching the surface; or use a number of such wires, until a film or succession of patches of copper forms; then remove these wires, and allow deposit to go on.-SIGMA. save annoyance and trouble by having a new crown [34669.]-Repairing Gas Holder.-You will put in at once; you cannot make a successful job of it by patching it up; still you may glue a piece of indiarubber cloth, such as is used for gas bags inside; this may make it last a little longer.-W. J. LANCASTER. [34671.]-Explanation Wanted. - Maxwell's "Theory of Heat" gives Professor James Thompson's explanation of this phenomenon as due to surface tension. The thin layer of liquid on the sides of the glass becomes more watery by the evaporation of the alcohol. This increases the superficial tension at the sides of the glass, and causes the surface to be dragged from the strong wine to the weak. The watery portion is always uppermost, and creeps up the sides of the glass, dragging the stronger wine after it, till the quantity of the fluid becomes so great that the different portions mix, and the drop runs down the side.-J. BROWN, Belfast. [34673.]-G. N. 8ft. Engines.-I beg to hand "N. Z." the following date and numbers of 8ft. single bogie engines:-Nos. 1, 8, in 1870; 33, in 1871; 22, 48, in 1874; 34, 47, 53, in 1875; 62, 94, 321, in 1876; 69, 98, 544, 545, in 1877; 548, 547, 548, 549, and 60, in 1878. There are some others which I do not know. No. 60 is the latest; it came out in Septem |