380 CHEMICAL DISCOVERY AND INVENTION 



of the factory. The raw material is cotton waste, which is specially 

 prepared for the explosive manufacturer. First it is hand picked 

 in order to remove all foreign matter as much as possible, and it 

 it amazing to see how much rubbish in the form of pieces of wire, 

 wood, nails, etc., is thus removed. Next it is teased and dried, 

 because cotton ordinarily contains about 10 per cent of moisture 

 and this water would needlessly dilute the nitrating acids. The 

 photograph (Fig. 133) shows a drying plant in use at Waltham 

 Abbey. Here it is exposed to a temperature of about 80 C. for 

 twenty minutes. It is then weighed up, according to the older 

 method introduced by Sir Frederick Abel, into lots of 1 J Ib. called 

 a charge, and is kept dry in an air-tight box till it is dipped. 



The acids used consist of a mixture of 1 part by weight of 

 strong nitric acid of specific gravity 1-5, with 3 parts by weight 

 of strong sulphuric acid of specific gravity 1*84. Mixing the 

 acids is attended by evolution of heat and the mixture is allowed 

 to become completely cool before it is run into the cast-iron 

 dipping tank. 



The charges of cotton are immersed in the acid for a few 

 minutes, then placed on a grating and the excess of acid squeezed 

 out. The partially changed cotton, still saturated with acid, is 

 placed in an earthenware covered pot standing in water, and left 

 for about twelve hours (Fig. 134). The nitration is then complete, 

 and the contents of the pots are lifted out by tongs and placed 

 in a centrifugal machine, where the excess of acid is wrung out. 

 The gun-cotton is then placed in a tank full of running water 

 till the water no longer answers to a test for acid. 



To remove the last traces of acid the cotton requires to be 

 boiled with water repeatedly. It is then reduced to pulp by 

 means of a machine similar in construction to the machines 

 used by paper-makers. It is then in a very fine state of division, 

 and, suspended in water, is passed by a pipe into the " poaching " 

 machine, where paddles keep the fine pulp agitated with water 

 and thoroughly wash every portion of it. After some hours 

 a small quantity of lime-water, whiting, and caustic soda is 

 added so as to leave the cotton pulp slightly alkaline. It is then 

 drawn off by means of a vacuum pump, and the pulp strained 

 off in measured quantities into moulds, where pressure is applied 

 sufficient to reduce the substance to the condition of a solid cake 

 hard enough to bear handling. Finally, the moulded cotton is 

 submitted to hydraulic pressure amounting to about five tons 



