THE CHEMICAL NEWS. VOL. XXXIX. No. 1015. AN EXAMINATION OF DR. PAVY'S METHOD OF By OTTO HEHNER, F.C.S., F.I.C. THE glowing account given by Dr. Pavy (CHEMICAL NEWS, vol. xxxix., p. 77) of the results obtained in determining glucose by means of ammoniated Fehling solution has doubtless induced many chemists to repeat Dr. Pavy's experiments and to test the accuracy of his method. 120 c.c. of ordinary Fehling solution are mixed with 300 c.c. of strong ammonia (sp. gr. o.88) and diluted to 1000 C.C. 100 c.c. of this liquid, containing 12 c.c. Fehling solution and capable of oxidising, according to Dr. Pavy, o'05 grm. glucose, were used in the following experiments instead of 40 c.c., as recommended by Dr. Pavy, in order to obtain results comparable without calculation with those furnished by io c.c. of ordinary Fehling solution. The mode of titration was precisely that described by Dr. Pavy. Following thus Dr. Pavy's directions I was surprised to obtain results widely differing from his, inasmuch as in a long series of experiments I found a difference of about 8 per cent in the total amount of glucose when determining it both by the ordinary copper solution and by the same rendered ammoniacal, the latter furnishing the higher results. In order to obtain corresponding results I had to dilute about 130 c.c. of Fehling solution with ammonia and water to 1000 c.c., instead of 120 c.c. as found by Dr. Pavy. The copper solution used in these experiments contained 400 c.c. of soda solution (of 114 sp. gr.) per litre, and the sugar solution (inverted sugar) was quite neutral; hence there could not possibly be too large a quantity of alkali, against which Dr. Pavy warned in his paper. Thus it appears that the smaller the quantity of fixed alkali, the smaller also the amount of sugar the copper solution is capable of oxidising; in fact, when no caustic soda at all is present, as in the last of the above experiments, I molecule of glucose requires exactly 8 molecules of cupric oxide for oxidation. With ordinary Fehling solution the ratio is 5 molecules; with the same rendered ammoniacal and containing no less than 120 grms. NaHO per litre, 6 molecules; and, lastly, the same without soda, 8 molecules. But the reaction without fixed alkali takes place exceedingly slowly, and on that account the endpoint is not easy to hit off. Instead, therefore, of guarding against too large a quantity of alkali, it is of far greater importance to avoid a deficiency, and good results can only be obtained by doubling the quantity of soda usually taken in the preparation of the cupro-tartrate solution. On the other hand, a much smaller excess of soda influences the result than is stated by Dr. Pavy, who found an addition of 5 grms. to 100 c.c. of the ammoniacal solution, or 417 grms. to the litre of Fehling solution without influence, whilst my results, which I have verified over and over again, show that even 2 grms. to 100 c.c. of the ammoniated solution, or 166 to the litre of Fehling, show a small but quite perceptible alteration. Thus the limits of alkali allowable or necessary are not so wide as might appear. If the proportions given by me are adhered to, the method is capable of furnishing excellent results. The solution containing the glucose should be added drop by drop to the ammoniacal copper solution, kept gently simmering. The end-point of the reaction is beautifully sharp, and titrations of the same liquid will never differ by more than o'r c.c. of the sugar solution. The action is, however, somewhat slower than with ordinary Fehling liquid. By suitable arrangements the ammonia can readily be absorbed and any nuisance avoided which would water-result from its entering the atmosphere. I then prepared another quantity of Fehling_solution, employing 480 c.c. soda, as recommended by Fresenius. I tested this both without and with the addition of ammonia, by titration with an invert sugar solution, obtained by heating 10153 grms. pure cane-sugar dissolved in 150 c.c. of water, with 10 c.c. strong HCl, on the bath, neutralising, and diluting to 250 c.c. 10 c.c. of Fehling solution required 1170 c.c. sugar solution. 10 c.c. Fehling + 1 grm. NaHO used 1165 c.c. sugar solution. The results show quite conclusively that Fehling solution prepared with 480 c.c. of soda of 114 sp. gr., corresponding to about 68 grms. NaHO per litre, does not give results concordant with the ratio stated by Dr. Pavy, and also that additions of very small quantities of soda steadily but perceptibly alter that ratio, until 50 grms. of soda per litre have been added to that already contained in the liquid, when further addition of soda, up to more than 80 grms., is without influence. Between these limits, namely with a total of 120 to 150 grms. of soda It must not, however, be taken for granted that the ratio holding good between the ordinary and the ammoniated copper solution is valid also in the case of other reducing saccharine matters. Dextrose and lævulose act equally, but I find that both milk sugar and maltose possess entirely different reducing power against two kinds of copper solutions. Thus a solution of pure milk-sugar acted as follows:- The ratio is therefore just contrary to that resulting by the action of glucose. The titration of milk-sugar, difficult and unsatisfactory as it is with the ordinary Fehling test, is, however, still more readily influenced by dilution, quantity of alkali, and rate of addition, and hence still less trustworthy in ammoniacal solution. Its action on that solution is very slow, and the end-point is somewhat difficult to observe, because on the experiment being much protracted cuprous oxide deposits and obscures the colour of the liquid. Maltwort acts similarly to milk-sugar, proving that it does not contain glucose, but another sugar, doubtless maltose. Experiments in reference to this matter are in progress. 54, Holborn Viaduct, London, April 12. 198 History of Detonating Agents. CHEMICAL NEWS, May 9, 1879. RECENT CONTRIBUTIONS TO THE HISTORY | thicknesses, with a Martini-Henry rifle, at short ranges, OF DETONATING AGENTS.* By Professor ABEL, C.B. F.R.S. Ir will now be evident why the readily yielding nature of the particles of liquid nitro-glycerine tends to counteract its great sensitiveness to detonation, and why, when the motion of the liquid particles is impeded by their admixture with solid matter, and when they are consequently placed in a position to resist mechanical motion by the force applied through the agency of detonation, its natural sensitiveness to detonation, and the rapidity with which it can be transmitted from particle to particle became fully developed. Again, the reduction of gun-cotton fibre to a fine state of division, which renders the material readily convertible into very compact and dense masses, places the particles in the condition most favourable to resist mechanical motion upon the application of a blow, or of the concussion resulting from a detonation; hence, compressed gun-cotton is readily susceptible of detonation in proportion to the extent of compression, or to its density and compactness, while loose gun-cotton wool, or the lightly twisted or compressed material, cannot be readily detonated, because the force applied is expended in imparting motion to the readily yielding particles of the mass. If the force applied through the agency of a detonator to a mass of explosive material just borders upon that required for the development of the detonation, or if the condition of the mass is such as hardly to present the requisite resistance to mechanical motion essential for its detonation, then results intermediate between the mechanical dispersion of the mass and its violent chemical dispersion or disintegration, i.e., detonation, are obtained. Thus frequent instances have been observed, especially in the experiments in the transmission of detonation through tubes, in which the initiative detonation has brought about an explosion attended with little, if any, destructive effect, portions of the mass being at the same time dispersed and occasionally inflamed. Not only have such results often been obtained with gun-cotton and dynamite, but even mercuric fulminate, exposed to the concussion of a distant detonation transmitted through a tube, has frequently been exploded in a manner quite distinct from the violent detonation developed in other instances. Silver fulminate, which under conditions detonates violently, even when only a particle of the mass is subjected to a sufficient disturbing influence, has been exploded without the usual demonstrations of force, by the transmitted effect of a detonation of mercuric fulminate. In these instances the violence of the concussion produced by the initiative detonation was only just bordering on that required for the development of detonation, and it appears probable that only some small portion of the mass operated upon was in a condition or position favourable to the action of the initiative blow. The remainder of the mass would then be dispersed by the gases developed from the detonated portion; in some instances the particles would be inflamed at the moment of their dispersion, in others they would even escape ignition. The latter appears to be always the case when gun-cotton is exploded by a blow from a hammer or falling weight. However carefully the arrangements are adjusted with a view to distribute such a blow uniformly over the entire mass struck, the concentration of a preponderance of the force applied upon some portion or portions of the entire mass, appears almost inevitable; hence only a small portion is actually detonated, the remainder being instantaneously dispersed by the gases suddenly generated while the weight is still resting upon the support. Some experiments made in firing at masses of compressed gun-cotton, differently arranged and of different Abstract of a Paper read before the Royal Institution of Great Britain, Friday, March 21, 1879. afforded interesting confirmation of the correctness of the explanation given of the operation of a blow upon masses of explosive material under different conditions. Disks of gun-cotton of the same density and diameter, but differing in thickness, were fired at; they were freely suspended, and their distance from the marksman was in all instances 100 yards. The thinnest disks were simply perforated by the bullets, not a particle of the gun-cotton being ignited. Somewhat thicker disks were inflamed by the impact of the bullet, while still thicker disks, fired at under the same conditions, were exploded, portions being in some instances dispersed in a burning state. was, however, obtained. These differences in effect, obdue to the difference in their power to resist mechanical tained with masses of different thickness and weight, are motion when struck by the bullet, and in the different amount of resistance to penetration presented by the thin and the thicker disks. No instance of detonation It has been explained that nitro-glycerin may be largely diluted with inert solid matters without the sensitiveness to detonation being reduced, while its detonation in open air becomes very much facilitated, because the mobility of the force of a blow or detonation, is very greatly dimi the particles, and their consequent tendency to yield to solid matter the case is different; for in such a mixture of nished. But if a solid explosive agent is diluted with inert the finely divided solid with non-explosive solid particles, there must be a partial and sometimes a complete separaparticles with which it is diluted; hence the sensitiveness tion of the particles of the explosive by the interposed inert to detonation is reduced, and its transmission by the particles is retarded or altogether impeded, by a diminution of the extent of contact between the substance to be detonated and the initiative detonation, and by the barrier which the interposed non-explosive particles oppose to the transmission of detonation. Thus a mixture of mercuric fulminate with more than one-fifth its weight of French chalk could not be detonated by means of one grain of pure fulminate enclosed in a copper capsule, which was inserted into the mixture; that quantity, similarly confined, sufficed to detonate undiluted fulminate through a tube 8 inches long and o'5 inch in diameter. In experiments made in this direction with finely divided gun-cotton, it was found that although dilution was an inert solid, applied in the solid form, reduced the sensitiveness of the material to detonation, this was not the case when it was incorporated with a salt soluble in water, the mixture being then compressed while in the wet state. The compressed masses thus obtained were, when dried, in a condition of greater rigidity than could be attained by submitting sure, because the crystallisation of the soluble salt used as undiluted gun-cotton to considerably more powerful presthe particles composing the mass more rig dly together. the diluent upon evaporation of the particles, cemented The gun-cotton was therefore presented in a form more capable of resisting the mechanical action of a small charge of fulminate than a more highly compressed undiluted gun cotton, and hence the reduction in sensitiveness due to the detonation of the explosive compound is nearly counterbalanced by the greater rigidity imparted to the mass. If a soluble oxidising agent (a nitrate or chlorate) be employed as the diluting material, the predisposition to chemical reaction between it and the guncotton (which is susceptible of some additional oxidation), appears to operate in conjunction with the effect of the salt in imparting rigidity to the mixture, thus rendering the minimum fulminate charge as undiluted gun-cotton. the latter quite as sensitive to the detonating action of Moreover, the interesting fact has been conclusively esta blished that these compressed mixtures of gun-cotton with a nitrate or a chlorate are much less indifferent to the in its pure state. Chlorated and nitrated gun-cotton are influence of detonating nitro-glycerin than gun-cotton detonated with certainty by means of oz. of nitroglycerin, whereas the detonation of 2 ozs. of the latter NEWS accomplished the detonation of ordinary compressed gun- | gun-cotton from time to time as the exterior becomes sufcotton only once in a large number of experiments. If compressed gun-cotton is diluted by impregnating the mass with a liquid, or with a solid which is introduced into the mass in a fused state, its susceptibility of detonation is reduced to a very much greater extent than by a corresponding quantity of a solid inert body, incorporated as such with the gun-cotton, the cause being the converse of that which operates in preventing a reduction of the sensitiveness to detonation of nitro-glycerin by its dilution with an inert solid. In this case the explosive liquid envelopes the solid diluent, and remains continuous throughout, occupying the spaces which exist between the solid particles; hence detonation is readily established and transmitted. But in the case of the solid explosive, the diluent, which is liquid, or at any rate is introduced into the mass in the liquid state, envelopes each particle of the solid, so that a film of inert material surrounds each, isolating it from its neighbours, and thus opposing resistance to the transmission of detonation, which is proportionate to the original porosity or absorbent power of the mass. While compressed gun-cotton, in the air-dry state, is detonated by 2 grains of mercuric fulminate imbedded in the material, its detonation by 15 grains, applied in the same manner, becomes doubtful when it contains 3 per cent of water, over and above the 2 per cent which exists normally in the air-dry substance. Specimens which had been impregnated with oil or soaked in melted fat and allowed to cool could not be detonated by means of 15 grains of fulminate. These diluted samples of gun-cotton could only be detonated by adding very considerably to the power of the initiative detonation; 100 grains of confined fulminate generally failed to detonate gun-cotton containing from 10 to 12 per cent of water, and if the amount reached 17 per cent, 200 grains of fulminate were needed to ensure its detonation. But moist or wet compressed gun-cotton is decidedly more susceptible of detonation by (dry) compressed guncotton itself than by mercuric fulminate. Thus 100 grains of dry gun-cotton, detonated through the agency of the ordinary fulminate fuze, suffice to detonate wet gun-cotton containing 17 per cent of water, though this result is somewhat uncertain. If the diluting agent amounts to 20 per cent, detonation is not certain with less than I oz. of dry gun-cotton, and if the compressed material be completely saturated with water (i.e., containing 30 to 35 per cent) 4 ozs. of the air-dry substance, applied in close contact, are needed to ensure its detonation. Detonation is transmitted through tubes from dry compressed gun-cotton to a moist disk of the material with the same facility as to the dry substance; and this is also the case with regard to the propagation of detonation from one mass of moist gun-cotton to another, in open air, all the pieces being ranged in a row, in contact with each other, provided that the piece first detonated does not contain less water than the others to which detonation is transmitted. Some curious results, obtained in experiments on the transmission of detonation, with gun-cotton containing different proportions of water, appeared to indicate that the character or quality of detonation developed by gun-cotton is subject to modification by the proportion of water which the latter contains. Gun-cotton containing 12 to 14 per cent of water is ignited with much difficulty on applying a highly heated body. As it leaves the hydraulic press upon being converted from the pulped state to masses having about the density of water, it contains about 15 per cent of water; in this condition it may be thrown on to a fire or held in a flame without exhibiting any tendency to burn; the masses may be perforated by means of a red-hot iron or with a drilling tool, and they may with perfect safety be cut into slices by means of saws revolving with great rapidity. If placed upon a fire and allowed to remain there, a feeble and transparent flame flickers over the surface of the wet ficiently dry to inflame; and in this way a piece of compressed gun-cotton will burn away very gradually indeed. A pile of boxes containing in all 6 cwts. of gun-cotton, impregnated with about 20 per cent of water, when surrounded by burning wood and shavings in a wooden building, was very gradually consumed, the gun-cotton burning as already described when the surfaces of the masses became partially dried. In two other experiments quantities of wet gun-cotton of 20 cwts. each, packed in one instance in a large, strong wooden case, and, in the other, in a number of strong packing cases, were placed in small magazines, very substantially constructed of concrete and brickwork. Large fires were kindled around the packages in each building, the doors being just left ajar. The entire contents of both buildings had burned away, without anything approaching explosive action, in less than two hours. This comparatively great safety of wet gun-cotton, coupled with the fact that its detonation in that condition may be readily accomplished through the agency of a small quantity of dry gun-cotton, which, through the medium of a fulminate fuze or detonator, is made to act as the initiative detonating agent, gives to gun-cotton important advantages over other violent explosive agents for purposes which involve the employment of more or less considerable quantities at one time, on account of the comparative safety attending its storage and the necessary manipulation of it. Moreover, it has been well established by experiments of many kinds carried out on a considerable scale, as well as by accurate scientific observations, that the detonation of wet guncotton is decidedly sharper or more violent than that of the dry material; a circumstance which affords an interesting illustration of the influence exerted by the physical condition of the mass upon the facility with which detonation is transmitted from particle to particle. In the determinations made by means of the Noble chronoscope, of the velocity with which detonation is transmitted along layers or trains of gun-cotton and nitro-glycerin, the lecturer has included experiments with gun-cotton containing different proportions of water. When the material contained 15 per cent of the liquid, some indications were obtained that the rate of transmission of detonation was a little higher than with dry gun-cotton; the difference was very decidedly in favour of wet gun-cotton, when the latter was thoroughly saturated with water. (With air-dry gun-cotton the mean rate of transmission ranged in several experiments between 17,000 and 18,900 feet per second; with gun-cotton containing about 30 per cent of water, the mean rate of transmission ranged between 19,300 and 19,950 feet per second.) The air in the masses of compressed gun-cotton being replaced entirely by the comparatively incompressible body, water, the particles of explosive are in a much more favourable condition to resist displacement by the force of the detonation, and hence they are more readily susceptible of sudden chemical disintegration. Moreover, the variations in the rate of travel of detonation in dry gun-cotton, resulting from differences in the compactness or rigidity of different masses of the material, are very greatly reduced, if not entirely eliminated, by saturating the disks with water and thus equalising their power of resisting motion by a sudden blow. Another striking illustration of the influence which the physical character of an explosive substance exercises over its susceptibility to detonation and the degree of facility with which its full explosive force is developed, is furnished by one of the most recently devised, and one of the most interesting of existing, explosive agents. Twelve years ago, soon after the process of producing compressed and granulated gun-cotton had been elaborated by the lecturer, it occurred to him to employ these forms of gun-cotton as vehicles for the application of nitroglycerin. A considerable proportion of the liquid was absorbed by the porous masses of gun-cotton, and a nitroglycerin preparation analogous in character to dynamite was 200 agent. Electric Lighting Apparatus at the Royal Albert Hall. CHEMICAL NEWS, EXHIBITION OF ELECTRIC LIGHTING ON Wednesday evening last an Exhibition of Electric Lighting Apparatus at the Royal Albert Hall was inaugurated by a lecture on the electric light, which was given by Mr. W. H. Preece, M.Inst.C.E., in the presence of the Prince of Wales, the Duke of Edinburgh, Prince Christian, and the Duke of Teck. Among the visitors were Lord Lindsay, Lord Rayleigh, Sir F. Pollock, Sir Charles Bright, Dr. Lyon Playfair, C.B., F.R.S., Dr. De la Rue, F.R.S., Prof. Tyndall, F.R.S., Prof. Abel, C.B., F.R.S., Dr. William Siemens, F.R.S., Dr. Frankland, F.R.S., Mr. Crookes, F.R.S., Mr. J. N. Lockyer, F.R.S., Prof. Ayrton, &c. thus obtained. The absorbent was in this case a violently explosive body instead of an inert solid as in dynamite, but the quantity of nitro-glycerin in a given weight of APPARATUS AT THE ROYAL ALBERT HALL. the preparation (to which the name of Glyoxilin was given), was considerably less than in the Kieselguhr-preparation; hence the latter was nearly on a point of equality with it, in regard to power, as an explosive Nobel has observed that if, instead of making use of the most explosive form of gun-cotton, or trinitro-cellulose, a lower product of nitration of cellulose (the so-called soluble or collodion gun-cotton) is added to nitro-glycerin, the liquid exerts a peculiar solvent action upon it, the fibrous material becoming gelatinised while the nitroglycerin becomes at the same time fixed, the two sub. stances furnishing a product having almost the characters of a compound. By macerating only from 7 to 10 per cent of soluble gun-cotton with go to 93 per cent of nitroglycerin, the whole becomes converted into an adhesive plastic material, more gummy than gelatinous in character, from which, if it be prepared with sufficient care, no nitro-glycerin will separate even by its exposure to heat in contact with bibulous paper, or by its prolonged immersion in water, the components being not easily susceptible of separation even through the agency of a solvent of both. As the nitro-glycerin is only diluted with a small proportion of a solidifying agent which is itself an explosive (though a somewhat feeble one), this blasting gelatine, as Nobel has called it, is more powerful not only than dynamite but also than the mixture of a smaller quantity of nitro-glycerin with the most explosive guncotton, as the liquid substance is decidedly the most violent explosive of the two. Moreover, as nitro-glycerin contains a small amount of oxygen in excess of that required for the perfect oxidation of its carbon and hydrogen constituents, while the soluble gun-cotton is deficient in the requisite oxygen for its complete transformation into thoroughly oxidised products, the result of an incorporation of the latter in small proportion with nitro-glycerin is the production of an explosive agent which contains the proportion of oxygen requisite for development of the maximum of chemical energy by the complete burning of the carbon and hydrogen, and hence this blasting gelatin should, theoretically, be even slightly more powerful as an explosive agent than pure nitro-glycerin. That such is the case has been well established by numerous experiments, but although this blasting gelatin may be detonated like dynamite by means of small quantities of confined detonating composition, when it is employed in strongly tamped blast-holes, or under conditions very favourable to the development of great initial pressure, it behaves very differently from that material, or other solid though plastic preparations of nitro-glycerin, if the attempt is made to detonate it when freely exposed to the air or only partially confined. It not only needs a much more considerable amount of strongly confined detonating composition than dynamite and similar preparations do, to bring about a detonation with it under those conditions; but when as much as 15 or 20 grains of confined fulminate are detonated in direct contact with it, although a sharp explosion occurs, little or no destructive action results, and a considerable portion of the charge operated upon is dispersed in a finely-divided condition. This dispersion appears to take place to some slight extent with dynamite also, when a small charge is detonated in open air, in consequence of its want of rigidity, though the amount of explosive which thus escapes detonation is very small as compared with the gelatin. (To be continued.) Temper of Steel.-M. Jarolimek maintains that steel can not only be hardened by immersion in boiling water, but even in boiling oil, melting lead, and melting zinc.Moniteur Scientifique. After the Prince of Wales had taken a seat on the right of the orchestra, the Duke of Edinburgh advanced to the front of the platform, and as Senior Vice-President of the Council of the Albert Hall introduced the Lecturer, who began by demonstrating that all systems of artificial illumination are dependent upon the production of heat. Some brilliant experiments were introduced to show that the greatest concentration of heat can be produced by electric currents in overcoming resistance. When this resistance is the air itself the electric arc is the result: when it is a wire or carbon rod we have light by incandescence. The discussion at the present time was whether light by the arc or by incandescence is to be the light of the future. The arc gives two and a half times the intensity of light given by incandescence by the same power. Mr. Preece showed that the improved methods now employed for the production of electricity by mechanical means is due to the development of Faraday's discovery that electric currents are produced by the rapid rotation of coils of wire in a powerful magnetic field, Faraday's original apparatus for showing this being exhibited by the Royal Institution. The electric light dependent on incandescence was practically illustrated by the lamps of Werdermann and the AngloAmerican Light Company. That dependent on the arc was shown by the regulators of Serrin, Siemens, Rapieff, and Wallace. The form of light based on the arc, but independent of regulators, called the candle, was illustrated by those of Wilde and Jablochkoff. Mr. Preece also introduced to the audience a powerful lamp called the "holophote," which is about to be introduced into the ports at Spithead, with a view to testing their value in detecting the advance of an enemy's torpedo. The many shortcomings of the electric light-such as the noise, the flickering, the deep shadows-were referred to, as well as such advantages as the absence of smoke, and the purification instead of the poisoning of the air in large buildings. The electric light was pronounced to be at the present time in the tentative stage, there being, as Mr. Preece remarked, three stages of every physical invention—the theoretic, when it is the dream of the philosopher; then the tentative stage, when it is the dream of the capitalist; and the third stage, when the practical man realises these dreams. The lecture was very warmly applauded. At its conclusion the Duke of Edinburgh proposed, on behalf of the Council of the Royal Albert Hall, a vote of thanks to Mr. Preece for his lecture. In the course of his speech His Royal Highness said that the Council of the Royal Albert Hall was anxious to employ the electric light even in its present imperfect condition in lighting the building, and would persevere until something satisfactory was accom. plished. The vote of thanks was seconded by His Royal Highness the Prince of Wales. The Exhibition will remain open until Saturday, and on Friday evening, at 8 o'clock, an explanatory lecture will be given by Mr. J. N. Shoolbred. The Council has endeavoured to make the collection of apparatus embrace the entire scope of all applications into which electric light strictly enters; and also as completely representa. NEWS tive as possible of all the various methods hitherto | own boiling-point, the bulb is filled with the liquid, and devised for the production of the electric light by mechanical means. PROCEEDINGS OF SOCIETIES. CHEMICAL SOCIETY. Dr. WARREN DE LA RUE, President, in the Chair, THE minutes of the previous meeting were read and confirmed. The following certificate was lead for the first time:-J. Sakurai. The PRESIDENT then called on Dr. W. RAMSAY to read a paper "On the Volumes of Liquids at their Boiling-points obtainable from Unit Volumes of their Gases." Kopp, in 1855, pointed out that the specific gravities of organic compounds show a certain regularity with regard to each other. If the molecular weights of various compounds be divided by their respective specific gravities at their boiling points, a series of numbers is obtained, which Kopp ultimately named specific volumes. Kopp's method o determining the volume of a liquid at its boiling-point (the only point at which volumes are comparable, for at that point the vapour-tensions of all liquids are equal) was to ascertain the boiling-point with great accuracy, to determine the specific gravity of some known temperature, and calculate the volume required by means of the coefficient of expansion. This process involves the use of complicated and expensive apparatus, and necessitates laborious calculation. Before describing the apparatus used by himself, the author discusses the precise conceptions involved in the expressions used by Kopp, &c.-" Atomic volume," "molecular volume," and "specific volume:" specific volume as used by Kopp I = molecular weight specific gravity suspended by a platinum wire in a glass vessel resembling amounts of heat evolved in the formation of these sub- Method of Precipitating Manganese entirely as Dioxide, By molecular weight is meant the specific gravity of the I 5059°2 |