CHEMICAL NEWS, May 28, 1804. Volumetric Estimation of Tannic and Gallic Acids, &c. On the Volumetric Estimation of Tannic and Gallic Acids, Iron, Manganese, &c., by MORITZ MITTENZWEY." THE known disposition of tannic acid in alkaline solution to absorb oxygen from the air affords an excellent means of estimating this body for technical purposes. The estimation can be conveniently made in the simple apparatus here figured and described. The air in a bottle (A), capable of holding about a litre and a-half, communicates with the atmosphere by the bent tubes (B) and (c), the latter being drawn out at the end (D) to the diameter of about one or one and a-half millimetres. The two glass tubes are united by means of a moderately long piece of indiarubber tubing (E), provided with a pinchcock (F) to close it; and the lower glass tube is fixed in the neck of the bottle by a bored cork, or, better, a caoutchouc stopper (G). same In executing the analysis it is absolutely necessary that the air in the bottle should be perfectly renewed, and the temperature of all reaching the fluid be the as that of the laboratory. As soon as the absorbing lye (which should amount to 150 or 250 c.c.) is prepared, the bottle should be perfectly closed, and then the pinchcock opened just for a moment, so that the pressure of the internal and external air may be equalised. The absorption of the oxygen is then hastened by strongly shaking the bottle, which must be wrapped in a cloth to avoid raising the temperature by the warmth of the hand. After each shaking, water must be allowed to flow into the bottle (A) from a weighed quantity in a beaker (B, Fig. 2), so that the fluid in the two vessels may attain the same level, as shown in the drawing. 253 2 c.c., and with gallic acid only 12 c.c. From six to ten experiments can be carried on simultaneously with ease, and indeed with advantage. The best alkaline solution to use is a soda solution containing 2 or 3 per cent. of caustic soda, or a potash solution with from 3 to 5 per cent. of the caustic alkali. Experiments have proved strong solutions to be useless; for example, one gramme of tannic acid in a potash solution containing 35 per cent. of alkali only absorbed 22 c.c. of oxygen. Further experiments confirmed this unexpected result. It has been already remarked that gallic acid absorbs oxygen with much greater readiness than tannic. One gramme of tannic acid, after shaking for 60 seconds, only absorbed 234 c.c.; while 07 gramme of gallic acid, after shaking for the same time, absorbed 71 c.c. of oxygen, the same proportion of each acid taking up when the absorption is complete one and the same volume (175 c.c.). We have here an indication of a means of estimating the two acids in the presence of each other. Suppose, for example, we have a substance, 2 grammes of which absorb 140 c.c., this will answer to 1+0=0.800 grammes of tannic acid, or to 10.0,7 = 0.560 of gallic acid. For a second and decisive experiment, we now weigh as much of the substance as should combine with 175 c.c., in this case 2. 178 2.500 grammes, and shake this strongly with the lye for 60 seconds. Suppose, after this, we have 40 c.c. absorbed, we have then a decisive proof of the presence of both acids, and we can draw a conclusion as to their respective proportions. It must be observed that in these experiments an equal weight of the substance, equally strong alkaline solutions, and a flask of equal size, and of similar form (about 14 litre capacity), are indispensable conditions. The following table, which gives the means of the numbers obtained in three experiments after shaking for sixty seconds, show sufficiently concordant results: 1'000 grammes Tannic acid) absorbed 23'4 c.c. 0'000 0*900 0°070 0'570 0'300 O'200 Gallic acid Tannic acid) Gallic acid J Tannic acid) Gallic acid J Tannic acid 61.0 c. c. The experiment is ended when, after repeated shakings, no more water runs from B-to A, and the difference in the weight of the water in the beaker in grammes gives the amount of oxygen absorbed in cubic centimetres, which can be corrected for the standard temperature and pressure. 0'560 O'Coo 0'700 A rather roundabout but quite conclusive experiment may be made in the following way :-The mixture to be estimated is dissolved in a known quantity of water, and the tannic precipitated by gelatine; the gallic acid solution is then transferred to the absorption bottle to be estimated. A second experiment is then made with the mixture, and so all necessary data for the calculation are obtained. In making use of the process to determine the tannic acid in leather, gall nuts, sumach, bark, &c., we proceed I. For Gallic and Tannic Acid.-Place in the in the same way as with pure tannin. If the amount of bottle about 200 c.c. of a 3 per cent. potash or soda tannic acid usually present in the substance is not solution, then drop in one gramme of tannic or gallic already known, it is advisable to make a preliminary acid loosely wrapped in paper, and proceed as above de-ceed with the quantity calculated to absorb 175 c.c. By experiment with a small quantity, and afterwards proscribed. The absorption is at first rapid, and in the case of gallic acid is soon complete; with tannic acid a longer time is required. One gramme of tannic acid will absorb the same amount of oxygen as 07 gramme of gallic acid, namely, 175 c.c. at 20° C. In twelve experiments the greatest variation in the case of tannic acid amounted to only * Journal für Prakt. Chemie, No. 2, 1864, p. 81. VOL. IX. No. 234.-MAY 28, 1864. To Estimate Tannin in Leather.-From 4 to 7 grammes of the leather is cut into the thinnest possible slices, which are digested in about 200 c.c. of warm water; after cooling from 7 to 10 grammes of stick potash wrapped in paper is dropped into the flask, and the shaking proceeded with. With sumach and oak bark the same method is followed, or a hot-filtered decoction is used. The results with the decoction always differ from those with the substance itself, the latter being higher, which seems to show that a portion of the tannic acid withstands the solvent action of the water. Gall nuts, catechu in powder may be estimated in the same way as pure tannic acid. II. Iron Compounds. These must be reduced to the state of protoxide by means of zinc, and the excess of acid neutralised with caustic potash or soda. (Ammonia and the carbonated alkalies must be avoided.) The solution is then poured into the absorption-flask and pieces of potash wrapped in paper are then dropped in. The absorption is complete in a very short time. For accuracy this process is second to none, and may be recommended in preference to that of Margueritte and Fuchs, since it requires fewer precautions. 50 c.c. of a solution of protoxide which contained 1395 Fe absorbed in three experiments 148 o c.c., 148°44 c.c., and 1484 c.c. of oxygen at 19° C.; the mean = 148 28 c.c., which at this temperature weigh o.1987 grammes, answering to 1391 grammes of iron. III. Manganese Compounds.-As these are easily reduced to the state of protoxide, the estimation is made in the same way as in the case of protoxide of iron, but it is necessary to know to what extent the protoxide of manganese unites with iron. Further experiments are required to determine this point, and the following proportional numbers are only the results of some few experiments that have led to the conclusion that one part by weight of absorbed oxygen corresponds to 4'34 parts by weight of manganese, which may be calculated as the oxide Mn,O,. In the absence of more complete researches it is superfluous to discuss the rational formula of the resulting oxide; but one thing is certain-namely, that the oxidation does not proceed so far as the state of binoxide. The estimation of manganese in the presence of iron is performed in two operations-one with the iron in the state of protoxide, and the other with the iron in the state of peroxide, and the absorption observed in the two cases. The combination of the two results will give the desired explanation. Active oxygen may be estimated in a similar way, by means of a solution of protoxide of iron. Indigo may be valued in the following way :-In a well-closed glass bottle finely-powdered indigo is reduced by means of potash or lime and a protosalt of iron, under a layer of mineral oil. When the precipitate has completely deposited, a certain volume of the clear solution of indigo-white is removed by means of a pipette, care being taken that a layer of oil swims on the surface of the solution. The pipette is then emptied into the absorption bottle, which must also contain oil, and the shaking is continued until the indigo blue is re-formed. According to theory, 8 parts by weight of combined oxygen answer to 131 parts of indigo blue; or, for one gramme of indigo blue 45'7 c.c. of oxygen at 20° C. are required. From these numbers we may see at once what degree of accuracy this way of analysing indigo promises. TECHNICAL CHEMISTRY. Conversion of Salt Meat into Fresh; a further Application of Dialysis, by A. A. WHITELAW. As an appendix to the notice of my process for the utilisation of brine (published in the CHEMICAL NEWS for March 26), I now beg to direct attention to a modification of that process, applicable to ships at sea, by which the quality of the meat supplied to the men may be much improved, and their food varied. 'The salt meat is placed in a dialytic bag made of untanned skin, or other suitable material, and the bag filled nearly, but not quite, full of brine from the beef barrel. The dialyser is then placed in sea water, and the process allowed to go on for several days, till the brine in the dialytic bag is within 1° or 2° of Twadde's meat and brine are sufficiently fresh for use, or till the hydrometer of the same strength of sea water. In this way, as the brine becomes freed from salt, the beef, which, by the action of salt, has been contracted, gives its salt to the brine in the bag, and so the process goes on, the beef expanding like a sponge, and gradually taking up a great part of the natural juice that it had previously lost in the salting process. In this way no loss of juice is sustained by steeping, and the brine left in the bags, after a nightly dialysis in fresh water, can be used for soup. Thoroughly salted beef, without bone, takes up nearly one-third its weight of juice, and this absorption takes place gradually as the strength of the brine in the dialyser becomes reduced. Meat thus treated-being, in fact, fresh meat-may be cooked in a variety of ways that are obviously not available for salt meat; and so the food of sailors, and, consequently, their health, may be improved. 55, Sidney Street, Glasgow. PROCEEDINGS OF SOCIETIES. ROYAL INSTITUTION OF GREAT BRITAIN. Friday, April 15, 1864. ment. 9 "On the Chemical History and Application of Gun-cotton," by Professor ABEL, F.R.S., Chemist to the War DepartTHE history of gun-cotton affords an interesting illustration of the facility with which the full development of a discovery may be retarded, if not altogether arrested, for a time, by hasty attempts to apply it to practical purposes before its nature has been sufficiently studied and deterthat he had discovered a new explosive compound, which mined. When Schönbein, in the autumn of 1846, announced he believed would prove a substitute for gunpowder, the statement attracted general attention, and attempts were made with little delay in different countries to apply the material to purposes for which gunpowder hitherto had been alone used. Schönbein, and Böttger (who appears to have discovered gun-cotton independently shortly after the former had produced it) lost little time in submitting their discovery to the German Confederation; and a committee was appointed for its investigation, by whom guncotton was eventually pronounced inapplicable as a substitute for gunpowder. immediately after the method of its preparation was pubIn this country, gun-cotton was experimented with lished by Schönbein. Researches were instituted into its nature, preparation, &c., by Porrett and Teschemacher, John Taylor, Gladstone, and others. A few experiments were made on its application as a propelling and mining agent, and the manufacture of the material upon a con- period taken an active interest in Baron von Lenk's invessiderable scale was set on foot by Messrs. Hall, the well-tigations. After upwards of one year's experiments, a known gunpowder-makers at Faversham, a patent having system of rifled field and mountain-guns, to be employed been previously taken out in this country for the produc- with gun-cotton which had been elaborated by von Lenk, tion of gun-cotton according to Schönbein's process. This was introduced into the Austrian service. Thirty batteries factory had, however, not been long in operation before a of these guns were equipped, and it was considered as very disastrous explosion occurred at the works, by which definitely settled that gun-cotton would before long be a number of men lost their lives, and which was ascribed introduced into the service in the place of gunpowder, for to the spontaneous ignition of the gun-cotton, by the jury artillery purposes. In 1862, however, an explosion occurred who endeavoured to investigate its cause. From that time at Simmering, near Vienna, where both gunpowder and the manufacture of gun-cotton upon any considerable scale gun-cotton were stored, and this disaster appears to have was abandoned in England, and no important contributions fortified to such an extent the arguments which were to our knowledge of this material were made until, in 1854, adduced against the employment of gun-cotton by its Hadow published the results of some valuable investiga- opponents in the artillery service that its use in this direction tions, which served to furnish a far more definite know- was again put a stop to for a time. Ultimately a Committee ledge regarding the true constitution and proper method of Investigation was appointed, which consisted in part of of producing gun-cotton than had hitherto existed. eminent scientific men, and which appears, after careful deliberation, to have reported highly in favour of the stability, and important properties as an explosive, of the material,- -a report which was supported by the favourable opinion entertained of gun-cotton by the Austrian engineers, in whose name Baron von Ebner prepared a very complete and interesting account of the properties and effects of the agent, with particular reference to mining and other engineering operations. In France, gun-cotton was also made the subject of experiments as early as the winter of 1846, and its manufacture was carried on at the Government powder works at Bouchet, near Paris. Some interesting balistic experiments were instituted, under the direction of Piobert, Morin, and other men of eminence, with gun-cotton in comparison with different kinds of gunpowder, the results of which indicated that, for producing equal effects to those furnished by a given weight of gun-cotton, it was necessary to employ a double quantity of sporting powder, three times the quantity of musket powder, and four times the weight of cannon powder. It was also found that the best results appeared to be obtained by arranging the gun-cotton so that it should occupy the same space as the charge of gunpowder required to produce an equal effect; and other data were arrived at, which show that the investigators were being led to work in a direction similar to that afterwards so successfully pursued by Baron von Lenk in Austria. Unfortunately, however, disastrous explosions occurred at the works at Bouchet, one as early as March, 1847, in a drying chamber, and two, following closely upon each other, in 1848. One of these took place in a magazine near which it was believed that nobody had been for several days; the other occurred also in a magazine where guncotton was being packed, and on this occasion several lives were lost. These disasters appear to have put an end, until quite recently, to experiments with gun-cotton in France. After the material had been pronounced upon unfavourably by the Committee of the German Confederation, one of its members, Baron von Lenk, continued to devote himself to its study, and with such success, it appears, that a Committee was eventually appointed by the Austrian Government in 1852 to inquire fully into the merits of the material. A sum of money was paid to Schönbein and Böttger in recognition of the value of their discovery, and an experimental manufactory of gun-cotton was established at the Castle of Hirtenberg, near Vienna. A particular form of cannon was devised by Baron von Lenk for employment with gun-cotton, of which a 12-pounder battery was established. The performances of these guns were considered sufficiently satisfactory to warrant the preparation of four more batteries, which were sent to the Army of Observation in Galicia in 1855, but did not go into active service. It appears that, in consequence of a want of uniformity in the effects of the gun-cotton, and of an injurious effect upon the guns, added probably to the prejudice entertained against it by the artillery, the material fell into disfavour, and its application in cannon was for a time abandoned. It was received, however, with much Gun-cotton appears, therefore, to have been again restored to favour in Austria, but no official accounts have reached England up to the present time, with regard to its employment in the recent war operations in that country. In the spring of 1862, full details relating to the manufacture and modes of applying gun-cotton were communicated by the Austrian Government to that of Her Majesty, and the War Office chemist was at once instructed to institute experiments upon the manufacture of gun-cotton, and In the upon its chemical constitution and stability. autumn of that year General Sabine directed the attention of the British Association to the results obtained with gun-cotton in Austria, and a combined committee of engineers and chemists was appointed to inquire into the subject. At the meeting of the Association in 1863, this committee presented a report, which was based upon information received partly from General von Lenk, who had been permitted by the Austrian Government to visit this country for the purpose of communicating fully with the British Association on the subject, and partly upon the results already arrived at in the experiments instituted by the lecturer under the direction of the Secretary of State for War. Subsequently a committee of investigation was appointed by the latter, under the presidency of General Sabine, composed of scientific men connected with the Royal Society and British Association, and of military and naval officers of considerable experience; and this committee has been entrusted with the full investigation of the properties of gun-cotton, as improved by Baron von Lenk, with reference to its applications to military, naval, engineering, and industrial purposes. The chemical constitution of gun-cotton, concerning which the opinions of chemists were divided until 1854, has been conclusively established by the researches of Hadow. In the formation of substitution-products by the action of nitric acid upon cotton or cellulose, three atoms of the latter appear to enter together into the chemical change, and the number of atoms of hydrogen replaced by peroxide of nitrogen in the treble atom of celluloseC18H30O15-3 (C&H10Os) may be nine, eight, seven, or six, according to the degree greater favour by the engineers, and was applied with great success to mining and submarine operations. Meanwhile, Baron von Lenk's labours to perfect gun-cotton as a material for artillery purposes were unceasing; and at the close of the Italian war the subject of its application was again thoroughly re-opened at the instigation of Count Degenfeld, then Minister of War, who had at an earlier this being the substance first produced by Pelouze in an (H21 C18 15 H, impure condition, in 1838, by the action of very concentrated nitric acid upon paper, or fabrics of cotton, or linen, and afterwards obtained in a purer form by Schönbein, who employed a mixture of concentrated nitric and sulphuric acids for the treatment of cotton wool; the object of the sulphuric acid being to abstract water of hydration from the nitric acid, and also to prevent the action of the nitric acid from being interfered with by the water which is produced, as the chemical transformation of the cotton into gun-cotton proceeds. The formation of trinitro-cellulose is represented by the following equation : The lowest substitution-product from cotton, of those named above, appears to have the same composition as the substance which Braconnet first obtained in 1832, by dissolving starch in cold concentrated nitric acid, and adding water to the solution, when a white, highly combustible substance is precipitated, to which the name of Xyloïdin was given. The substitution-products from cotton, intermediate between the lowest and highest, are soluble in mixtures of ether and alcohol, and furnish by their solution the important material collodion, so invaluable in connection with photography, surgery, experimental electricity, &c. According to Schönbein's original prescription, the cotton was to be saturated with a mixture of one part of nitric (of sp. gr. 15) and three parts of sulphuric acid (sp. gr. 185), and allowed to stand for one hour. In operating upon a small scale, the treatment of cotton with the acid for that period is quite sufficient to effect its complete conversion into the most explosive product pyrozilin, or trinitrocellulose; but when the quantity of cotton treated at one time is considerable, especially if it is not very loose and open, its complete conversion into pyroxilin is not effected with certainty unless it be allowed to remain in the acid for several hours. This accounts in great measure for the want of uniformity observed in the composition of gun-cotton and its effects as an explosive, in the earlier experiments instituted; and it is, moreover, very possible that the want of stability and, consequently, even some of the accidents which it was considered could only be ascribed to the spontaneous ignition of the material, might have been due to the comparatively unstable character of the lower products of substitution, some of which existed in the imperfectly-prepared gun-cotton. The system of manufacture of gun-cotton elaborated by General von Lenk is founded upon that described by Schönbein; the improvements which the former has adopted all contribute importantly to the production, of a thoroughly uniform and pure gun-cotton; there is only one step in his process which is certainly not essential, and about the possible utility of which chemical authorities are decidedly at variance with General von Lenk. The following is an outline of the process of manufacture of gun-cotton as practised by Lenk. The cotton, in the form of loose yarn of different sizes, made up into hanks, is purified from certain foreign vegetable substances by treatment for a brief period with a weak solution of potashes, and subsequent washing. It is then suspended in a well-ventilated hot air chamber until all moisture has been expelled, when it is tranferred to air-tight boxes or jars, and at once removed to the dipping tank, or vessel where its saturation with the mixed acid is effected. The acids of the specific gravity prescribed by Schönbein are very intimately mixed in a suitable apparatus in the proportions originally indicated by that chemist, i.e., three parts by weight of sulphuric acid to one of nitric acid. The mixture is always prepared some time before it is required, in order that it may become perfectly cool. The cotton is immersed in a bath of the mixed acids, one skein at a time, and stirred about for a few minutes, until it has become thoroughly saturated with the acids; it is then transferred to a shelf in this dipping trough, where it is allowed to drain and slightly pressed to remove any large excess of acid, and is afterwards placed in an earthenware jar provided with a tightly-fitting lid, which receives six or eight skeins, weighing from two to four ounces each. The cotton is tightly pressed down in the jar, and if there be not sufficient acid present just to cover the mass, a little more is added: the proportion of acid to be left in contact with the cotton being about ten and a-half pounds to one pound of the latter. The charged jars are set aside for forty-eight hours in a cool place, where, moreover, they are kept surrounded by water to prevent the occurrence of any elevation of temperature and consequent destructive action of the acids upon the gun-cotton. The same precaution is also taken with the dipping. trough, as considerable heat is generated during the first saturation of the cotton with the acids. At the expiration of forty-eight hours the gun-cotton is transferred from the jars to a centrifugal machine, by the aid of which the excess of acid is removed as perfectly as is possible by mechanical means, the gun-cotton being afterwards only slightly moist to the touch. The skeins are then immersed singly into water, and moved about briskly, so as to become completely saturated with it as quickly as possible. This result is best accomplished by plunging the skeins under a fall of water, so that they become at once thoroughly drenched. If they are simply thrown into water and allowed to remain at rest, the heat produced by the union of a portion of the free acids, with a little water would be so great as to establish at once a destructive action upon the gun-cotton by the acid present. The washing of the separate skeins is continued until no acidity can be detected in them by the taste; they are then arranged in frames or crates and immersed in a rapid stream of water, where they remain undisturbed for two or three weeks. They are afterwards washed by hand to free them from mechanical impurities derived from the stream, and are immersed for a short time in a dilute boiling solution of potashes. After this treatment, they are returned to the stream, where they again remain for several days. Upon their removal they are once more washed by hand, with soap if necessary; the pure guncotton then only requires drying by sufficient exposure to air at a temperature of about 27° C. to render it ready for use. A supplementary process is, however, adopted by General von Leuk, about the possible advantage or use of which his opinion is not shared by others, as already stated. This treatment consists in immersing the air-dried gun-cotton in a moderately strong, hot solution of soluble glass (silicate of potassa or soda) for a sufficient period to allow it to become completely impregnated, removing the excess of liquid by means of the centrifugal machine; thoroughly drying the gun-cotton thus "silicated," and finally washing it once more for some time until all alkali is abstracted. Lenk considers that by this treatment some silica becomes deposited within the fibres of the gun-cotton, which, on the one hand, assists in moderating the rapidity with which the material burns; and, on the other hand, exercises (in some not very evident manner) a preservative effect upon the gun-cotton, rendering it less prone to undergo even slight changes by keeping. The mineral matter contained in pure gun-cotton which has not been submitted to this particular treatment amounts to about 1 per cent. The proportions found in specimens which have been "silicated" in Austria and in this country, according to Lenk's directions, varies between 15 and 2 per cent. It is difficult to understand how the addition of 1 per cent. to the mineral matter, in the form chiefly of silicate of lime and magnesia (the bases being derived from the water used in the final washing) which are deposited upon and between the fibres in a pulverulent form, can influence to any material extent either the rate of combustion or the keeping qualities of the product obtained by Leuk's system of manufacture. Gun-cotton, prepared according to the system just described, is exceedingly uniform in composition. The analyses of samples prepared both in Austria and at Waltham Abbey have furnished results corresponding accurately to those required by the formula per cent. H In its ordinary air-dry condition, it contains, very uniformly, about 2 per cent. of moisture-an amount which it absorbs again rapidly from the air when it has been dried. The proportion of water existing in the purified air-dried cotton, before conversion, is generally about 6 When pure gun-cotton is exposed to a very moist atmosphere or kept in a damp locality, it will absorb as much as from 6 to 7 per cent. ; but if it be then exposed to air of average dryness, it very speedily parts with all but the 2 per cent. of moisture which it contains in its normal condition. It may be preserved in a damp or wet state apparently for an indefinite period without injury; for if afterwards dried by exposure to air, it exhibits no signs of change. In these respects it possesses important advantages over gunpowder. The normal proportion of hygroscopic moisture in that substance varies three-quarters and one per cent.; but if exposed in any way to the influence of a moist atmosphere, it continues to absorb water until, however firm the grains may have originally been, it becomes quite pasty. It need scarcely be stated that when once gunpowder has become damp, it can no longer be restored to a serviceable condition, except by being again submitted to the processes of manufacture, starting almost from the commencement. cautions of experience, combined with more searching investigations than have hitherto been instituted, upon the possibility of its undergoing change when under the influence of moderate heat, alone or combined with that of moisture, or when preserved under a variety of conditions, are unquestionably indispensable before its claims to perfect permanence can be considered as properly established. It has already been ascertained, by very recent experiments of the lecturer, that gun-cotton prepared and purified with the most scrupulous care speedily undergoes some amount of decomposition when exposed to temperatures ranging from 32° to 66° C.; it remains to be seen whether such decomposition, if once established by exposure of gun-cotton to some temperature within the above limit, will cease permanently when the material is removed from the influence of heat, or whether preor efficient supplementary processes can be adopted in the manufacture, to counteract the tendency to change exhibited by gun-cotton under the above circumstances. These are only some of the points which need patient investigation before it is positively known whether the requisite confidence can be placed in the material, as an agent susceptible of substitution for gunpowder. It has been ingeniously argued that a slight indication of spontaneous change in gun-cotton need give rise to no alarm, because gunpowder is also liable to slight spontaneous change, reference being made to the fact that a very minute proportion of the sulphur in that material has been noticed to undergo oxidation. It need hardly be stated that such a minute change cannot have the slightest effect upon the stability of the mechanical mixture gunpowder, in which variations as regards purity and proporPerhaps the most vital considerations bearing upon the tions of ingredients occur to an extent which render this possibility of applying gun-cotton to important practical change of absolute insignificance; whereas, in the case of purposes, are those which relate to the risk likely to be gun-cotton, as now manufactured, the development of incurred in its manufacture and preservation, in large acid, however minute the proportion, may very possibly quantities. The manufacture of gun-cotton is, unques-brium in a compound, the stability of which is based upon give rise to an important disturbance of chemical equilitionably, much safer than that of gunpowder; in fact, there is no possibility of accident until the final drying process is reached, as, in all the other stages, the material is always wet, and therefore harmless. With the adoption of a proper system of warming and ventilation in the drying-chamber, the last operation is certainly not a more dangerous one than that of gunpowder. The question of the safe preservation of gun-cotton cannot, as yet, be so easily and satisfactorily disposed of. Specimens of guncotton exist which were prepared according to Schönbein's directions in 1846, and which have undergone no change whatever; on the other hand, it is well known that guncotton which was believed to have been perfectly purified, has become extremely acid, and has even undergone so complete a decomposition as to have become converted into oxalic acid and other organic products, when preserved in closed vessels, and especially when exposed continuously or occasionally to light. This susceptibility to chemical change has been particularly observed in samples of gun-cotton known to consist chiefly, or to contain some proportion, of the less explosive or lower substitution products (i.e., gun-cotton specially prepared for the manufacture of collodion). Hence it is very possible that such instances as are considered to have been well authenticated, of the spontaneous ignition of gun-cotton when stored in considerable quantities, or during exposure to very moderate heat, may have arisen, not simply from an imperfect purification of the material, but also from the more or less imperfect conversion of cotton into the most explosive and apparently most stable product. the perfect uniformity of its composition; and it may also be at once productive of further change by the tendency which the acid itself has to exert chemical action upon certain elements of the gun-cotton. The general properties of gun-cotton as an explosive agent have long been popularly known to be as follows:When inflamed or raised to a temperature ranging between 1378 and 150° C. it burns with a bright flash and large body of flame, unaccompanied by smoke, and leaves no appreciable residue. It is far more readily inflamed by powerparticular portion of a mass of loose gun-cotton between ful percussion than gunpowder; the compression of any rigid surfaces will prevent that part from burning when heat is applied. The products of combustion of gun-cotton considerable proportion of nitric oxide, and act rapidly in air redden litmus paper powerfully; they contain a and corrosively upon iron and gun-metal. The explosion form in which it was always prepared in the early days of of gun-cotton when in the loose, carded condition-the its discovery-resembles that of the fulminates in its violence and instantaneous character. In the open air it may be inflamed when in actual contact with gunpowder without igniting the latter; in a confined space, as in a shell or the barrel of a gun, the almost instantaneous rapidity of its explosion produces effects which are highly destructive as compared with those of gunpowder, while the projectile force exerted by it is comparatively small. There is no doubt that the improvements effected in the system of manufacture of gun-cotton have been instru--The members of the Academy appointed to consider mental in rendering it far more stable in character than it was in the early days of its production upon a considerable scale. At the same time, although General von Lenk and its warmest partisans consider that its unchangeability can no longer be disputed, a greater amount Professor of Chemistry to the Royal Academy. the Report of the Royal Commissioners have joined in the recommendation of a professorship of "chemistry as applicable to art." We have already advocated the appointment as most desirable, and hope the Academicians will soon give effect to the recommendation. |