EXPLOSIVES 381 



on the square inch, which leaves the cake so hard that it does 

 not yield perceptibly to pressure by the finger. 



Newer methods of nitration have been introduced by which a 

 larger quantity of cotton can be immersed in the acids at one 

 time. 



Centrifugal machines have been constructed which can be 

 rilled with the acids and a much larger weight of cotton, generally 

 about 17 Ibs., can be immersed. When the nitration is complete 

 the acid can be run off and the cotton drained by setting the 

 machine in motion. 



Another method employed at the Royal Factory, Waltham 

 Abbey, is known as the displacement process. The plant consists 

 of shallow earthenware circular pans grouped together in sets 

 of four. They are provided with perforated false bottoms, and 

 the bottom of each pan is connected with a pipe by which the 

 nitrating acid can be supplied, and a pipe by which the spent 

 acid can be drawn off. These pans will each take a charge of 

 20 Ib. of dry cotton. 



Hoods connected with an exhaust fan draw off the fumes 

 from the acids, and these hoods are made of aluminium, a metal 

 which is practically unacted on by nitric acid. When all the 

 cotton is immersed perforated earthenware plates are laid on 

 top of the cotton to keep it under the acid, and a thin layer of 

 water is cautiously run over the surface of the acid. This prevents 

 the escape of acid fumes and allows of the removal of the hoods. 

 After two and a half hours the nitration is complete ; the spent 

 acid can be drawn off, and an equivalent quantity of water run 

 into each pan. In this way the spent acid is displaced .much 

 more completely than by the older methods. 



After draining off the water from the pans the gun-cotton is 

 ready for the processes of purification already described. 



Up to this point the nitrated cotton has been treated as non- 

 explosive, but in order to dry it, it is removed to one of the 

 stoves in the danger area. Dry gun-cotton is one of the most 

 dangerous explosives, as when dry and warm it is very liable to 

 explode by friction, and the greatest care has to be exercised in 

 handling it. 



In the production of gun-cotton the composition of the acid 

 mixture is of the utmost importance, and if the sulphuric acid 

 present is deficient in amount, or the proportion of water formed 

 in the process is allowed to exceed a certain amount the nitration 



