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NEWS

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"MONSIEUR,

"Paris, 27 Août, 1878.

"La division de la règle géodésique, que nous faisons pour l'Association Géodésique Internationale, est terminée depuis quelques jours.

Nous avons pensé que vous ne seriez pas mécontent d'apprendre que cette operation à parfaitement réussi, et que c'est au métal que nous attribuons la facilité avec laquelle nous avons pu l'exécuter.

"Le platine iridié de M. Matthey est incontestablement supérieur au platine ordinaire, pour la confection des règles divisées. Il est exempt de ces pailles qu'on rencontre toujours dans ce dernier, et se laisse polir au charbon. On peut, sans danger, enlever les rébarbes des traits et les conserver très beaux. Le platine ordinaire ne peut-être poli qu'au papier à émeré, et l'on est toujours exposé à gâter la division quand on procéde à l'ébarbage. C'est là un inconvénient très-grave.

"Nous ne pouvons que vous remercier, Monsieur, d'avoir mis à notre disposition un metal qui modifie singulièrement les difficultés qu'on rencontre dans la fabrication d'une règle géodésique, et nous vous prions de recevoir l'assurance de nos sentiments les plus distingues. "Brunner Freres.

In the year 1876 the suggestion was made to supersede the rectangular form by a tubular one, and I was requested to produce one of the following dimensions:Length, 1002 centims.; exterior diameter, 37 millims.; interior diameter, 35 millims.; with rounded ends, one having an extension of small tube 4 millims. exterior diameter, 2 millims. interior diameter, 40 millims. long, which I did by the system of tube-making with autogenous joints adopted by me with excellent results for the last twenty years, employing for the purpose an alloy prepared as above described. These proved to be so satisfactory that I have since made others, both round and square, of various dimensions, as lately shown at the Paris Exhibition.

Iridio-platinum alloy has now been proved to possess the following among many advantages for standard rules and weights:

It is almost indestructible, has extreme rigidity, especially in the tube form, and a most beautifully polished surface can be obtained upon it; its coefficient of elasticity is very great, whilst for standard weights its high density

Ruthenium .. Iron

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and gave the density of 21.614.

With such a high density its coefficient of elasticity is 22*200000, one of the highest known, whilst its malleability and ductility are almost without limit.

The volume of the kilogram thus prepared is only 46 266 c.c., it displaces 2.267 c.c. less than the kilogram of the archives of France, and on this account, as on many others, is of course preferable.

The results I have arrived at in preparing alloys of higher grades, viz., 25, 30, 40, and 50 per cent of iridium, are as follows:

The alloy of 20 per cent iridium is, as I have stated already, malleable and ductile.

25 per cent can only with great difficulty and waste be worked into sheet and wire when heated at low temperature. 30 per cent and 40 per cent with great difficulty only at a temperature little less than melting-point, being brittle when cold, but with a grain of great beauty and fineness.

50 per cent I have as yet failed to work up into forms other than castings beyond what I can effect by pressure when in a semi-fused condition.

The general results of my work on this alloy would lead me, therefore, to make the following recommendations. For the manufacture of standard rules to use an alloy of not less than 85 per cent platinum and 15 per cent iridium, adopting the tubular form.

For the standard weights to use an alloy of not less than 80 per cent platinum and 20 per cent iridium, adopting the form now generally made.

Finally, following the expression of the great French chemist, M. Dumas, I hope by these labours "d'avoir enriché l'outillage scientifique d'un alliage doué des propriétés précieuse.”

RECENT CONTRIBUTIONS TO THE HISTORY
OF DETONATING AGENTS.*
By Professor ABEL, C.B., F.R.S.
(Continued from p. 166.)

IT has been stated that detonation can be transmitted from one mass of gun-cotton or dynamite to another through intervening air-spaces. The extent to which such spaces can be introduced without checking detonation is obviously regulated by the size of the masses of explosive detonated; but the distance of air-space through which the detonation of a moderate quantity of the explosive agent will communicate to similar masses are very limited, a space of 2 inches being sufficient to prevent the detonation produced by a mass of 8 ozs. of gun-cotton, freely exposed, from communicating to contiguous ones. If the dispersion of the force is prevented in part, and direction is given to the gases violently projected from the centre of detonation, the power of transmitting detonation to separated masses of explosive is increased to a remarkable degree. This is readily accomplished through the agency of tubes, the charge first detonated being just inserted

Abstract of a Paper read before the Royal Institution of Great Britain, Friday, March 21, 1879.

178

History of Detonating Agents.

{CHEMICAL NEWS,

April 25, 1879.

in tightly-fitting india-rubber tubes. These differences appeared on further investigation not to be ascribable, to any important extent, if at all, to the difference in the nature of the material composing the tubes, but to be simply, or at any rate almost entirely, due to differences in the condition of the inner surfaces of the tubes. Thus, brass tubes, the inner surfaces of which were highly polished, and paper tubes, when coated inside with highly glazed paper, transmitted the detonation of the silver fulminate to about the same distance as the glass tubes; on the other hand, when the inner surfaces of the latter were slightly roughened by coating them with a film of fine powder, such as French chalk, they no longer transmitted detonation to anything like the distance which they did when the inner surfaces were in the normally smooth condition. Other very slight obstacles to the unimpeded passage of the gas-wave through the tubes were found greatly to reduce the facility with which detonation could be transmitted by means of tubes. Thus, when a diaphragm of thin bibulous paper was inserted into the glass tube about half-way between the two extremities, detonation was not transmitted, even with the employment of about six times the quantity of fulminate that gave the result with certainty under ordinary conditions; and, similarly, the transmission of detonation by increased charges of mercuric fulminate and of gun-cotton was prevented by the introduction into the tubes of light tufts of carded cotton-wool just sufficient in quantity to shut out the light in looking through the tubes.

into one extremity, while that to which the detonation | tubes with several layers of paper, or by encasing them is to be transmitted is inserted into the other; or separate charges may be placed at different distances inside a long tube, with long intervening spaces, the initiative charge being inserted at one end. A few illustrations of the results thus obtained may be given. The detonation of a I-oz. disk of gun-cotton in the open air will not transmit detonation with certainty to other disks placed at a greater distance than half an inch from it; but if it be just inserted into one of an iron tube 2 feet long and 1.25 inch in diameter, a similar disk, or even a plug of loose gun-cotton, inserted into the other extremity of the tube, will invariably be detonated. With employment of 2 ozs. of gun-cotton, in a tube of the same material, thickness, and diameter, detonation was transmitted to a distance of 5 feet. In tubes of the same kind, of very considerable length, 2-oz. disks of gun-cotton, placed at intervals of 2 feet, were detonated through the initiative detonation of one such disk inserted into one extremity of the tube. In other experiments a long tube of this kind was fitted with branch pipes, 2 feet long, at those parts where the intermediate disks were placed, and charges of gun-cotton were placed at the extremities of these pipes. By the initiative detonation of 1 oz. of gun-cotton all the charges were detonated, the effect on the air being that of one single explosion. The results obtained with equal quantities of guncotton varied with the diameter, strength, and nature of the material of the tubes used. Dynamite and mercuric fulminate, applied to their own detonation, furnished results quite analogous to those obtained with gun-cotton; but in applying fulminate to the detonation of gun-cotton through the agency of tubes, some singular and instructive results were obtained, for an account of which the lecturer referred to his Memoir on this subject.

Silver fulminate was employed for the purpose of instituting more precise experiments than could be made in operating on a larger scale, with gun-cotton, on the influence of the material composing the tubes, of the condition of their inner surfaces, and other variable circumstances, upon the transmission of detonation. Half a grain of silver fulminate, freely exposed and ignited by a heated body, will transmit detonation to some of the compound placed at a distance of 3 inches from it, but does not do so with certainty through a distance of 4 inches. But when the quantity of the fulminate is just inserted into one end of a stout glass tube, o'5 inch in diameter and 3 feet long, its detonation is invariably induced by that of a similar quantity of the fulminate placed just inside the other extremity of the tube; this result is uncertain when the length of the tubes of the same thickness and diameter exceeds 3 feet 3 inches. Glass tubes were found to transmit the detonation of silver fulminate much more rapidly than tubes of several other materials of the same diameter and thickness of substance. Thus, with the employment of double the quantity of fulminate required to transmit the detonation with certainty through a glass tube of the kind described, 3 feet in length, it was only possible to obtain a similar result through a pewter tube 31.5 inches long, a brass tube 23.7 inches long, an india-rubber tube 15.8 inches long, and a paper tube 118 inches long. The difference in the results obtained was not ascribable to a difference in the escape of force on the instant of detonation, in consequence of the fracture of the tube, nor to the expenditure of force in work done upon the tube at the seat of detonation, since the glass tubes were always destroyed by the first explosion to a much greater distance along their length than any of the others, and the brass tubes, which were in no way injured at the seat of explosion, did not transmit detonation to so great a distance as the pewter tubes, which were always deeply indented. The transmission of detonation appeared, also, not to be favoured by the sonorosity or the pitch of the tube employed, as the sonorous brass tube was not found to favour the transmission to the same extent as the pewter tube. Moreover, the transmission of detonation by the glass tubes was not found to be at all affected by coating these

Among several other interesting results furnished by an examination into the conditions governing and results attending the transmission of detonation by tubes, a remarkable want of reciprocity was found to exist between mercuric fulminate and gun-cotton. The latter substance is more susceptible to the detonative power of mercuric fulminate than of any other substance, as will presently be further shown. The quality of fulminate required to detonate gun-cotton is regulated by the degree to which the sharpness of its own detonation is increased by the amount of resistance to rupture offered by the envelope in which the fulminate is confined. From 20 to 30 grains are required if the detonative agent is confined in a thin case of wood or in several wrappings of paper; but as small a quantity as 2 grains of the fulminate suffices to effect the detonation of compressed gun-cotton, provided the fulminate be confined in a case of stout metal (sheet tin), and be closely surrounded by being tightly imbedded in the mass of gun-cotton. If there be no close contact between the two, the quantity of fulminate must be very considerably increased to ensure the detonation of the gun-cotton; and, in attempting to transmit detonation from mercuric fulminate to gun-cotton by means of tubes, it was found necessary to employ comparatively very large quantities of fulminate in order to accomplish this, even through short lengths of tubes. But when the quantity of fulminate used reaches certain limits, the detonanation may be transmitted from it to gun-cotton through very long lengths of tube. In applying gun-cotton, on the other hand, to accomplish the detonation of mercuric fulminate, it was found that this result could be attained, and through considerable lengths of tube (7 feet and upwards), by means of very much smaller quantities of guncotton than is needed of fulminate to induce the detonation of gun-cotton through the corresponding distances.

This want of reciprocity between two detonating agents corresponds to one even more remarkable, which was ob served by the lecturer in his earlier investigations on this subject. In the first place it was found that the detonation of oz. of gun-cotton (the smallest quantity that can be thus applied) induced the simultaneous detonation of nitro-glycerin, enclosed in a vessel of sheet-tin, and placed at a distance of 1 inch from the gun-cotton; while withoz. of the latter the same effect was produced with an intervening space of 3 inches between the two substances. But on attempting to apply nitro-glycerin to

the detonation of gun-cotton, the quantity of the former, which was detonated in close contact with compressed gun-cotton, was gradually increased in the first instance to oz., and subsequently even to 2 ozs., without accomplishing the detonation of the latter, which was simply dispersed in a fine state of division, in all instances but one, in a large number of experiments.

The force developed by the detonation of nitro-glycerin was found, by careful comparison of the relative destructive effects of corresponding quantities, to be decidedly greater than that of the fulminate, of which from 2 to 5 grains suffice for developing the detonation of gun-cotton, when it is in close contact with them. The non-susceptibility of gun-cotton to detonation by nitro-glycerin is therefore, it need scarcely be said, not ascribable to any deficiency in mechanical force suddenly applied when the nitro-glycerin is detonated.

That the power possessed by different very highly explosive substances, of inducing the detonation of such bodies as gun-cotton and nitro-glycerin is not solely ascribable to the operation of mechanical force very suddenly developed, is indicated not only by the singular inertness of guncotton to the influence of nitro-glycerin as a detonating agent, but also by a comparison of the behaviour of other detonating substances with that of the mercuric fulminate, when applied to the detonation of gun-cotton. Thus, the detonation of silver fulminate is very decidedly sharper than that of the mercury compound, yet it is in no way superior to the latter in its power as an initiative detonating agent; indeed, a somewhat larger amount of it appeared to be required than of the mercury salt to induce detonation of gun-cotton with certainty. Again, the iodide and chloride of nitrogen are far more susceptible of sudden detonation than the silver fulminate; yet while 5 grains of the latter, confined in a stout metal envelope, suffice to detonate gun-cotton, 50 grains of chloride of nitrogen confined by water, appeared to be the minimum amount with which the detonation of gun-cotton could be accomplished with certainty, while no success attended the employment of confined iodide of nitrogen in quantities ranging up to 100 grains.

The incompatibility of these results with the general conclusion, based upon numerous and greatly varied experiments, that the facility with which the detonation of gun-cotton and nitro-glycerin, and bodies of a similar character as explosives, is induced by an initiative detonation, is proportionate to the mechanical force aided by the heat developed by the latter, led the lecturer to the conclusion that a synchronism or similarity in character or quality of the vibrations developed by the detonation of particular substances, operates in favouring the detonation of one such substance by the initiative detonation of a small quantity of another, while in the absence of such synchronism, a much more powerful detonation, or the application of much greater force, would be needed to effect the detonation of the material operated upon. This view has received considerable support from results since obtained by other experimenters, especially by MM. Champion and Pellet; but the subject is one which still needs further experimental elucidation.

(To be continued);

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I HAVE made the well-known reaction

3SiF4+2H20=2H2SiF6+SiO2

the basis of a volumetric determination of fluorine, estimating the quantity of hydro-fluosilicic acid formed from a given weight of a fluoride by means of a standard alkali solution.¦

It is impossible to titrate the hydro-fluosilicic acid directly, because as soon as an alkaline reaction is reached the silico-fluoride is decomposed and an acid reaction is But when indicated, which change goes on slowly. barium chloride and an equal volume of alcohol are added to the solution, barium silico-fluoride is precipitated from the solution, and an equivalent amount of hydrochloric acid is liberated, which can be titrated; by this means, using litmus as an indicator, I was enabled to get some very satisfactory results, but the turbidity caused by the barium silico-fluoride interfered with the change of colour of the litmus, and cochineal I was not able to use at all. On further experimenting I found that potassium chloride possessed some advantages over barium chloride. On adding potassium chloride and an equal volume of alcohol, potassium silico-fluoride is precipitated from the solution, and an equivalent of hydrochloric acid is liberated, but the potassium silico-fluoride is a very transparent precipitate, and does not interfere with the change of colour of the indicators. It is necessary that alcohol shall make up at least one-half the volume of the liquid to be titrated, so as to precipitate the potassium silico-fluoride as completely as possible.

The apparatus needed is very simple, and consists of a gasometer of ten or more litres capacity, a few flasks of about 150 c.c. capacity, a few large plain U-tubes 18 centimetres long and 2 centimetres diameter, made without any narrowing in the bend, and a heavy iron I may be heated with a plate supported properly so that lamp.

The fluoride is weighed out accurately into one of the flasks; unless it is a silicate, 10 grms. of powdered and ignited quartz are added, and two or three pieces of quartz These last facilitate about the size of kidney beans. mixing up the powder when the flask is shaken. The contents of the flask are then drenched with from 30 to 40 c.c. of sulphuric acid which has been previously heated and allowed to cool. The flask is tightly closed with a doubly perforated cork; from the gasometer dry air is passed into the flask by means of a glass tube which reaches nearly to the bottom. The silicon fluoride mixed with air passes from the decomposing flask first through a small U-tube, made from ordinary glass tubing, 5 millimetres in diameter, and kept cool by being placed in a beaker of cold water, then into one of the large U-tubes intended for decomposing the silicon fluoride and absorbing the hydro-fluosilicic acid. The U-tube contains a solution of potassium chloride mixed with an equal volume of alcohol; the escaping gas is made to bubble through this, and to ensure complete decomposition a second smaller U-tube is attached to the first: the first tube absorbs nearly all the acid, the second contains only traces. The decomposing flask is supported on the iron plate; by its side is placed a second flask containing sulphuric acid and a thermometer supported so that its bulb dips into the acid; the lamp heating the plate is placed midway between the flasks, and the heat is regulated so that the temperature of the acid remains between 150° and 160° C.

The decomposition is continued two hours in ordinary cases, and during that time a continuous current of air is forced through the apparatus, amounting to from 5 to 6 litres for the two hours, while the contents of the decomposing flask are frequently agitated by shaking.

Aiter the decomposition and aspiration are completed the contents of the U-tubes are titrated. For this purpose they may be transferred to a beaker, the tubes being rinsed with alcohol and water, or better, the acid may be titrated directly in the U-tubes. In order that the alcohol may make up one-half the volume of the liquid after the titration is completed, add a few c.c. of alcohol before titrating, or where 15 or more c.c. are to be added use a standard alkali one-half of whose volume is alcohol. A the separated silicic acid sticks to the sides of the U-tube it is necessary to have prepared a glass rod bent a little at one end to scrape off and break up this silica.

180

Sanitary Condition of Air in Public Schools.

I have found by experiment that a simple dry U-tube between the decomposing flask and absorbing tube is sufficient to condense any sulphuric acid that may go over from the heated acid.

When fluorine is to be determined in a mineral containing chlorine, as in the case of an apatite, substitute for the empty U-tube one filled with fragments of pumice impregnated with perfectly anhydrous sulphate of copper. This will intercept any hydrochloric acid, and will also serve to condense any sulphuric acid vapour that may go over from the heated acid. The calculation is very simple. Every one equivalent of sodium carbonate equals one equivalent of hydro-fluosilicic acid or six of fluorine, hence the proportion

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CHEMICAL NEWS, April 25, 1879.

about so as to moisten the interior surface of the bottles, and thus hasten the absorption of carbon dioxide. The milky-looking liquid was transferred to small, widemouthed, glass-stoppered bottles, and after the barium carbonate had settled, 25 c.c. of the supernatant liquid were carefully titrated with a known solution of oxalic acid, turmeric paper being used to determine the point of neutralisation. The solution of oxalic acid was made of such strength that I c.c. corresponded to 1 m.grm. of carbon dioxide.

For calculating the volume of carbon dioxide in 10,000 volumes of air the following formula was used— 760(1+0.003665xt)p, Χ H(V-v)0 0019714

in which H represents the height of the barometer in millimetres, V the capacity of the flask, the volume of barium hydroxide solution used for absorption, t the temperature expressed in degrees of the Centigrade scale, and the amount in milligrms. of carbon dioxide in the air experimented upon.

It will be seen from the tabular statement that the amount of carbon dioxide found in several instances was as much as 25 volumes in 10,000, or one-quarter of one per cent. Whether this amount is sufficient of itself to render air decidedly unwholesome may be questioned, though all will admit that an increase of six times the normal quantity found in the atmosphere shows improper or defective ventilation. It was observed that in every instance where the amount of carbon dioxide reached 20 volumes in 10,000 or one-fifth of one per cent, the odour arising from other impurities of respiration was exceedingly offensive; and even where the amount was 10 in 10,000 this offensive odour was distinctly perceptible.

While no reliable method has yet been devised for the direct determination of organic impurities resulting from respiration, recognisable by the sense of smell, they evidently vary with the amount of carbon dioxide present, and may thus be indirectly estimated.

In the construction of these school buildings no provision whatever was made for ventilation other than by doors and windows, except some narrow flues in one of the buildings, and a ventilating-shaft at each of the four corners of one other, with openings entirely too small to

SANITARY CONDITION OF AIR IN PUBLIC be of much service. The General Superintendent of the

SCHOOLS.

By N. T. LUPTON, Vanderbilt University.

THE following series of determinations of carbon dioxide in air from the public schools of Nashville, Tennessee, was made at the request of the City Board of Health. The subject being one of general scientific interest, the results are submitted as a contribution to sanitary chemistry. (See Table cn next page.)

The above observations were made each day at from 12.30 to 1.30 p.m., and from an hour and a half to two hours after recess. In a few instances, as indicated, two bottles of air were taken at the same time from one and the same room, but at different parts of the room. The results are connected by brackets. In making the determinations of carbon dioxide the wellknown method of Pettenkofer was adopted, as it can be easily and rapidly performed, and gives accurate results. Four thin white glass bottles, one of 4950, two of 3950, and one of 3925 c.c. capacity, were used. The bottles were filled with air from about the middle of the rooms while the schools were in session, by means of a small hand-bellows, and after standing a few minutes to equalise temperature and pressure, were closed with well-fitting caoutchouc stoppers. They were then taken to the open air, and exactly 50 c.c. of a solution of barium hydroxide rapidly run into each, the bottles closed, carried to the laboratory, and allowed to remain two or three hours with occasional shaking; or, rather, the solution was moved

schools, appreciating the importance of ventilation, has established a rule which requires the teachers to lower the upper sash of each window a few inches on the side of the room opposite to that from which the wind may chance during recess the windows are required to be raised and to blow, so as to avoid draughts as much as possible, and the doors to be thrown open. It was evident during my visits that these rules were faithfully carried out by the teachers, and that where defective ventilation exists it is caused by defective construction of the room or by overcrowding of pupils. It is a question of grave importance whether the return of children overheated by play to a cold room for the resumption of their studies is not more dangerous to health than defective ventilation.

10.

per minute for one person for healthful respiration. Dr. Opinions differ in regard to the quantity of air required Arnott says that 20 cubic feet are necessary; Dr. Reed, and school-rooms, says "I have come to the conclusion Roscoe, in discussing certain experiments in barracks that 10 cubic feet per minute per head is insufficient to recalculating the amount of ventilation he uses the followmove completely the organic putrescent matter." For ing expression :

V1=V+Va+Va2 . . . . . Va1.

In which V represents the volume of air to be added to produce a given amount of impurity, V the volume of pure air, and a the ratio between the natural impurity in the air (0.04) and that found in the room under examination. Roscue determines only the first three terms of the series,

NEWS

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To determine, then, the quantity of air in its normal condition which must be added to one of the rooms containing 136 pupils so as to give in one hour and a half the percentage of carbon dioxide (0'3242) found, we proceed as follows;-If one person exhales o 686 cubic feet of this gas in one hour, 136 persons will exhale 139 944 cubic feet in one hour and a half. By a simple proportion we get the value of V, which, multiplied by the fraction in the equation whose terms are known, we get within reasonable limits the quantity of air with which 139.944 cubic feet of carbon dioxide must be mixed in order to make the percentage of this gas amount to 0.3242, the quantity actually found in the room. The calculation gives 49'242 cubic feet of air as necessary to reduce 139'944 cubic feet of carbon dioxide to o'3242 of the total bulk. This allows to each person 4 cubic feet per minute, which is not sufficient for healthful respiration.

From the column under "Cubic Feet of Air per Minute for One Person," which was calculated in the above manner, it will be seen that six of the rooms visited gave only 5 cubic feet or less of pure a'r per minute to each

person, a quantity insufficient for healthful occupancy according to all authorities. Eleven other rooms gave only 10 cubic feet or less per minute, an amount insufficient to remove the disagreeable odours of animal effluvia. In a few instances the temperature and percentage of moisture found below the geenrally recognised standard, but these may have been accidental.

The general management of these schools is worthy of praise. The systematic arrangement of studies, thoroughness of instruction, and excellence of discipline, are such as to enlist the sympathy of all classes and command the patronage of those who have children to educate; but the adoption of a more efficient system of ventilation is demanded in view of the facts presented and the important interests involved.

The Discussion on Mr. Hollway's New Process in Metallurgy. We have been requested to announce that a renewal of the discussion on Mr. Hollway's paper, "A New Application of Rapid Oxidation by which Sulphides are Utilised as Fuel," will take place at the Society of Arts on Wednesday evening next, April 30, at 8 o'clock. Dr. Roscoe, F.R.S., will preside.

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