April 5, 1900] 



NA TURE 



549 



than at any other stage in the manufacture. There are usually six 

 mills working in the same building, with partitions between. 

 Over the bed of each mill is a horizontal board, the " flash 

 board," which is connected with a tank of water overhead, the 

 arrangement being such that the upsetting of one tank dis- 

 charges the contents of the other tanks on to the corresponding 

 mill beds below, so that in the event of an accident the charge 

 is drowned in each case. The " mill-cake " is now broken 

 down between rollers, the "meal" produced being placed in 

 strong oak boxes and subjected to hydraulic pressure, thus 

 increasing its density and hardness, at the same time bringing 

 the ingredients into more intimate contact. After once more 

 breaking down the material (press-cake), the powder only requires 

 special treatment to adapt it for the various purposes for which 

 it is intended. 



Within the last half-centuiy an enormous alteration has taken 

 place in artillery, the old smooth-bore cannon, firing a round 

 shot, having gradually given place to heavy rifled cannon, firing 

 cylindrical projectiles and requiring very large powder charges. 

 This has naturally had its influence on the powder used, and 

 modifications have been introduced in two directions — first, 

 alteration in the form of powder, and second, in the proportions 

 of the ingredients. As the heavier guns were introduced, a 

 large grain powder which burned more slowly was adopted, 

 but further increase in the size of the guns led to the introduc- 

 tion of pebble powders, which in some cases consisted of cubes 

 of over an inch side. Such cubes having large available surface 

 evolved the usual gases in greater quantity at the start of the 

 combustion than towards the finish, since the surface became 

 gradually smaller, thus causing extra strain on the gun as the 

 projec ile was only just beginning to move. General Rodman, 

 an American officer, introduced prism powder to overcome this 

 difficulty, the charges being built up of perforated hexagonal 

 prisms in which combustion started in the perforations and pro- 

 ceeding, exposed more surface, the prisms finally breaking down 

 into what was virtually a pebble powder. 



In order to secure still further control over the pressure, modi- 

 fications in the proportions of the ingredients became necessary ; 

 the diminution of the sulphur and increase of the charcoal 

 causing slower combustion, and moreover the use of charcoal 

 prepared at a low temperature giving the so-called "cocoa- 

 powders." 



The products of the combustion of powder and its manner of 

 burning are largely influenced by the pressure, a property well 

 illustrated by the failure of a red-hot platinum wire to ignite a 

 mass of powder in a vacuum, only a few grains actually in con- 

 tact with the platinum undergoing combustion. The gaseous 

 products obtained are carbon dioxide, carbon monoxide and 

 nitrogen, other products being potassium carbonate, sulphate and 

 sulphide. The calculated gas yield at o° C. and 760 mm. pres- 

 sure is 264 '6 c.c, whilst Noble and Abel actually obtained by 

 experiment 26374 c.c , numbers agreeing very closely. At the 

 temperature of explosion this volume is enormously increased. 



In 1832, Braconnot found that starch, ligneous fibre and 

 similar substances when treated with strong nitric acid yielded 

 exceedingly combustible substances, and Pelouze in i8j8 ex- 

 tended the investigation to cotton and paper. Schonbein an- 

 nounced in 1845 his ability to make an explosive which he 

 termed gun cotton, and a year later Bottger made a similar 

 announcement, and on a conference being held between these 

 chemists their methods were found to be identical. The method 

 was not disclosed at the time, since it was hoped that the Ger- 

 man Government would purchase the secret, but in a very 

 short time several investigators solved the problem, and attempts 

 to make the new explosive commercially were common. Un- 

 fortunately the earlier product was unstable, and several dis- 

 astrous accidents occurred which led to the abandonment of the 

 experiments except in Austria. General von Lenk, who con- 

 tinued experimenting in that country, showed that if sufficient 

 care was taken to ensure complete nitration and to remove all 

 traces of free acid from the finished material, the substance was 

 stable. He introduced a method of manufacture which was 

 improved by Sir Frederick Abel in 1865. The physical character 

 of the cotton fibre is such that it presents every obstacle to the 

 removal of free acid, .since it is built up of capillaries, but by 

 reducing these tubes to the shortest possible length, as in Abel's 

 process, the removal of acid is facilitated. 



Since water is a product of the reaction of nitric acid on 

 cellulose, the nitric acid would become diluted, forming " collo- 

 dion cotton " instead of the more highly nitrated gun-cotton, 



NO. 1588, VOL. 61] 



and therefore sulphuric acid is used with the nitric acid to 

 absorb this water, the usual proportions being three parts by 

 weight of sulphuric acid ( i 84) to one part by weight of nitric 

 acid (I "52). Cotton waste, which has been picked, cleaned, cut 

 into short lengths and dried, is dipped in \\ lb. charges in the 

 acid, removed after five or six minutes, the excess of acid 

 squeezed out, and the cotton placed in cooled earthenware pots 

 for some twenty-four hours for nitration to be completed. The 

 gun-cotton now goes through the lengthy process for removal 

 of all traces of acid, starting with the removal of the greater 

 portion of the acid by a centrifugal extractor, washing in water 

 till no acid taste can be detected, boiling in water till free from 

 action on litmus, reducing to pulp in a hollander, and, finally, 

 the thorough washing of the pulp by more water. If the pro- 

 duct now satisfies the tests for purity, sufficient alkali — lime- 

 water, whiting and caustic soda — is added to leave from one 

 to two per cent, in the finished gun-cotton. The pulp is drawn 

 up into a vessel from which it can be run off" in measured 

 quantities into moulds fitted with perforated bottoms, the 

 water being drawn off by suction from below, and, finally, a 

 low hydraulic pressure is brought to bear on the semi-solid mass. 

 The blocks are taken to the press-house and submitted to a 

 pressure of some five tons per square inch, after which the 

 finished block will contain from twelve to sixteen per cent of 

 water. 



From its chemical reactions gun-colton must be regarded as 

 an ether of nitric acid, a view first suggested by Bechamp. The 

 point of ignition of the substance has been found to vary con- 

 siderably, ranging from 136° to 223° C, this difference being 

 probably due to variations in composition. Good gun-cotton 

 usually ignites between 180° and l84°C. The combustion is 

 extremely rapid when fired in loose unconfined masses, so rapid, 

 in fact, that it may be ignited on a heap of gunpowder without 

 affecting the latter. When struck between hard surfaces gun- 

 cotton detonates, but usually only in that portion which is 

 subjected to the blow. The volume of permanent gases evolved 

 by the explosion of gun-cotton, as stated by different observers, 

 has varied greatly. Macnab and Ristori give for nitrocellulose 

 — 13*30 per cent, nitrogen — 673c. c. per gram, calculated at o°C. 

 and 760 mm. Berthelot estimates the pressure developed by the 

 detonation of gun-cotton — sp. gr. fi — under constant volume 

 as 24,000 atmospheres or 160 tons per square inch. 



Various attempts have been made to adapt gun-colton for use 

 in guns, but the tendency to create undue pressure led to its 

 abandonment. In 1868, Mr. E. O. Brown, of Woolwich, 

 showed that wet gun-cotton could be detonated by the use of a 

 small charge of dry gun-colton with a fulminate detonator, and 

 since it can be stored and used in the moist state, it becomes one 

 of the safest explosives for use in submarine mines, torpedoes, 

 &c. 



Nitroglycerine is a substance of a similar chemical nature to 

 nitrocellulose, the principles of its formation and purification 

 being very similar, only in this case the materials and produce 

 are liquids, this rendering the operations of manufacture and 

 washing much less difficult. The glycerine is sprayed into the 

 acid mixture by compressed air injectors, care being taken that 

 the temperature during nitration does not rise above 30° C. The 

 nitroglycerine formed readily separates from the mixed acids, 

 and being insoluble in cold water, the washing is comparatively 

 simple. 



This explosive was discovered by Sobrero in 1847. Nitro- 

 glycerine is an oily liquid readily soluble in most organic 

 solvants, but becomes solid at three or four degrees above the 

 freezing point of water, and in this condition is less sensitive. 

 It detonates when heated to 257° C. , or by a sudden blow, yieldirig 

 carbon dioxide, oxygen, nitrogen and water. Being a fluid 

 under ordinary conditions, its uses as an explosive were limited, 

 and Nobel conceived the idea of mixing it with other substances 

 which would act as absorbents, first using charcoal and after- 

 wards an infusorial earth, " kieselguhr," and obtaining what he 

 termed "dynamite." 



In 1875, Mr. Alfred Nobel found that "collodion cotton"— 

 soluble gun-colton— could be converted by treatment with nitro- 

 glycerine into a jelly-like mass which was more trustworthy in 

 action than the components alone, and from its nature the sub- 

 stance was christened " blasting gelatine." The discovery is of 

 importance, for it was undoubtedly the stepping-stone from 

 which the well-known explosives ballistite, filite and cordite 

 were reached. In 1888, Nobel took out a patent for a smokeless 

 powder for use in guns, in which these ingredients were adopted 



