August 5, 1909] 



NA TURE 



179 



of producing a deposit in the bore, whicli it was hoped 

 would get rid of the difficulty of metallic fouling. Of 

 all these various substances the one which appeared to 

 answer the purpose most satisfactorily was refined vaseline, 

 and this material became the third ingredient of cordite 

 as eventually introduced into the British service. When 

 the manufacture was commenced on a large scale, vase- 

 line, which is the proprietary name of one of the refined 

 products of the distillation of petroleum, was replaced by 

 mineral jelly, the same material, but in a cruder form. 



The original object with which mineral jelly was intro- 

 duced was of no importance when cordite was substituted 

 for the black and brown powders used in large guns, but 

 in order to have bjit one nature of smokeless powder in 

 the service mineral jelly was added to all cordite, whether 

 for use in small arms or artillery. Subsequent experience 

 has demonstrated how very fortunate was the selection of 

 this material for rifle cordite and the e.xtension of its 

 use to all sizes of cordite. 



Mineral jelly is one of the best ingredients it is possible 

 to have in smokeless powders from the point of view of 

 their chemical stability. This important fact, not recog- 

 nised originally, was brought out in the following way. 

 In order to facilitate the explosion of cordite in blank 

 ammunition for the rifle it was cut into very thin flakes, 

 and the non-explosive mineral jelly was omitted from its 

 composition. After a comparatively short storage in a 

 hot climate the stability of the smokeless blank, as it 

 was called, was found to have suffered seriously, whereas 

 the stability of normal cordite containing mineral jelly 

 was not appreciably affected. These facts led to a 

 thorough investigation at Waltham Abbey of the action 

 of mineral jelly in preserving the stability of cordite, and 

 it was discovered that mineral jelly contained constituents 

 which had the valuable property of combining with the 

 decomposition products (the result of prolonged storage 

 of cordite at high temperatures) to form stable bodies, 

 thus removing these decomposition products, which un- 

 doubtedly exert a deteriorating influence on the cordite 

 from their sphere of action. 



When Abel was engaged on his researches in connection 

 with the production and properties of guncotton, it was 

 obvious to him that some test of a chemical nature was 

 required in order to ascertain whether or not the finished 

 guncotton had been thoroughly purified in manufacture. 

 It will be remembered that accidents occurred in the early 

 days of its production because this purification had not 

 been carried sufficiently far. The test which he devised 

 was based on the principle that if guncotton be subjected 

 to an elevated temperature, traces of oxides of nitrogen 

 will be given off, and will reveal their presence by acting 

 on a suitable reagent. 



The test is carried out by heating guncotton in a test- 

 tube placed in a water bath, and suspending over it a 

 strip of moistened filter paper impregnated with potassium 

 iodide and starch. If the purification of the guncotton 

 has not been sufficient, the discoloration of the test paper 

 takes place early ; as the result of experience Abel fixed 

 a time before which no reaction should take place. This 

 test, known as the Abel heat test, is a test for the purity 

 of guncotton and of nitroglycerine, and of freshly made 

 explosives containing either one or both of these in- 

 gredients. For this purpose no test has yet been devised 

 which equals it. But it was never intended to be, and 

 is not, a quantitative test, and is therefore only a rough 

 guide, though a very useful one, as to the stability of 

 an explosive which has been in store for more or less 

 prolonged periods, or under more or less adverse con- 

 ditions. 



Smokeless powders of the types dealt with are all sub- 

 ject to deterioration, and there is very little doubt that 

 this deterioration is for any given explosive a function 

 of the temperature of storage. The higher the tempera- 

 ture the more rapid the deterioration. 



The necessity, therefore, of some quantitative test which 

 would enable a judgment to be formed as to the extent 

 of deterioration suffered by any given sample of cordite 

 is obviously of great importance, because such a test 

 would afford the means of determining how much longer 

 it would be safe to store any given batch of cartridges 

 or lot of cordite at any given temperature. .Anv such test 



XO. 2075, VOL. 81] 



must be a heating test, and it must be possible to correlate 

 the temperature and duration of the test with any given 

 temperature and duration of storage. The rate of deteriora- 

 tion as a function of the temperature was determined by 

 Dr. Will for guncotton, and later by Dr. Robertson at 

 Waltham Abbey for nitroglycerine. From these and other 

 experiments carried out at Waltham Abbey, a factor of 

 increase in rate of deterioration of cordite with increase 

 of temperature was deduced. This factor having been 

 determined, what is known as the " silvered vessel test " 

 was worked out at the Royal Gunpowder Factory. In 

 this test, of which the details will be described presently, 

 cordite is heated in a specially designed vessel at 80° C, 

 a temperature not too far removed from those to be met 

 with when cordite is stored under the worst service con- 

 ditions, and the number of hours' heating at this tempera- 

 ture any given sample will stand before it shows signs 

 of active decomposition are ascertained. Then, by means 

 of an equation, containing the factor connecting rate of 

 increase of deterioration with rise in temperature, a_ calcu- 

 lation can be made converting the hours of heating at 

 80° C. the sample withstood to years and fractions of a 

 year it would stand at any given temperature of storage, 

 and therefore a knowledge is obtained of how much longer 

 it would be safe to store this cordite at any given tempera- 

 ture. 



This test was applied to a considerable number of 

 samples of known age and thermal history. From these 

 data, and knowing the number of hours at So° C. that 

 newly made cordite of good stability will stand before 

 showing signs of decomposition, the number of hours that 

 the different samples should stand the test were calculated. 

 When the samples were actually tested, the number of 

 hours' heating at 80° C. they withstood were in close 

 agreement with the number of hours it was calculated 

 thev should stand. 



The form of vessel in which the heating is carried out 

 is the well-known vacuum vessel of Sir James Dewar. 

 A glass bulb silvered externally is enclosed in an outer 

 bulb silvered internally. The space between the two is 

 highly evacuated for the purpose of limiting the dissipa- 

 tion of any heat evolved by exothermic changes _on_ the 

 one hand, and on the other for the purpose of minimising 

 the effect of accidental slight changes in temperature of 

 environment. 



In the centre of the inner bulb is situated the bulb of 

 a thermometer, the stem of which passes through a cork 

 in the neck of the vessel. A side tube is attached for the 

 purpose of making observations on the colour of the gases 

 evolved. For heating the vessel a bath is provided with 

 cylinders closed at the bottom, and wide enough to admit 

 the vessel to such a depth as the side tube will permit. 

 The bath is surrounded by insulating materials. The 

 vessels ^re packed in the cylinders with wool yarn, and 

 the tops of the cylinders are closed with felt discs to 

 exclude draughts. 



The bath is fitted with a gas regulator or other means 

 for securing that the temperature of the explosive is kept 

 constant. 



The cordite is coarsely ground, and 50 grams are used. 



Readings of the thermometer are taken at intervals, 

 and the time is noted when a rise of 2° C. in the tempera- 

 ture of the explosive above the temperature of 80° C. 

 occurs. At the same time, visual observations are made 

 as to the colour of the column of gas in the side tube, 

 since it is found that, previous to the rise in temperature 

 occurring, orange-coloured fumes of nitric peroxide are 

 evolved. When the temperature exceeds 82° C. the test 

 is complete, and the flask is withdrawn. The number 

 of hours which have elapsed since the start of the test 

 is the measure of the stability of the cordite. 



Until about sixty years ago, the only explosive known 

 for all purposes was gunpowder. With the discovery of 

 guncotton and nitroglycerine, gunpowder was gradually 

 replaced by them for' blasting purposes. In their early 

 days the two explosives were used singly, guncotton as 

 guncotton, nitroglycerine — first of all alone — and then as 

 dynamite. Later on the two were combined as blasting 

 gelatine and explosives of a similar nature, but it was 

 quite forty years after their discovery before either became 

 of practical use for propulsive purposes. 



