384 CHEMICAL DISCOVERY AND INVENTION 



" Should, however, the temperature continue to rise and pass 

 the danger mark then a large cock in the bottom of the nitrator 

 is opened, and the contents are rapidly discharged into a large 

 tank, containing water, outside the building, where the charge 

 is ' drowned,' and thereby the danger avoided of serious de- 

 composition and probable explosion. 



"When everything goes right the nitration of the charge is 

 usually completed in about one hour, the agitation with the air 

 is discontinued, and the separation of the nitroglycerine from 

 the acids takes place ; being lighter it comes to the top. A pipe 

 in which a glass window is fitted leads from the top of the nitrator- 

 separator to a pre- washing tank ; by allowing waste acid from 

 a previous operation to enter at the bottom the nitroglycerine 

 is forced over into the washing tank, and the flow of acid is 

 stopped whenever all the nitroglycerine has passed into the 

 washing tank, which can be observed through the window." In 

 the washing tank the nitroglycerine is stirred up repeatedly with 

 fresh water, then with a solution of sodium carbonate, and 

 finally with water. After this it is filtered to remove traces of 

 water or impurities. 



Nitroglycerine is a colourless oil of specific gravity 1-6, and 

 therefore sinks in water in which it is insoluble. It has a sweetish 

 taste and is poisonous. In minute doses it is used in medicine. 

 When a lighted match is applied it burns quietly away, but it 

 detonates violently when struck on an anvil by a hammer or by 

 sudden heating to 257 C. Nitroglycerine becomes solid when 

 exposed to frost and in use it requires to be thawed, an operation 

 attended by considerable risk. 



When nitroglycerine is exploded it yields a mixture of ca n 

 dioxide and nitrogen with 4 per cent of free oxygen, whe is 

 when nitrocellulose is fired the carbon dioxide and nitrogen are 

 accompanied by carbon monoxide and a considerable quantity 

 of free hydrogen. In the latter case the relative proportions of 

 these gases vary with the pressure developed in the space in 

 which explosion occurs. It appears that even when oxygen is 

 present in excess, oxides of nitrogen are never formed in a 

 normal explosion. Nitrous fumes are however formed when one 

 of these high explosives burns freely without explosion. 



In 1875 it was discovered by Alfred Nobel that when a low 

 grade of gun-cotton and nitroglycerine are mixed together the 

 cotton loses its fibrous or cellular structure and becomes gela- 



