142 GUN-COTTON. 



by various processes which the fibre has undergone, 

 in the different operations of the manufacturer. 



322. Pure lignin, or cellulose, as it is sometimes 

 termed, is scarcely at all acted on by acid or alkaline 

 solutions, either hot or cold, unless they are very 

 concentrated. Strong sulphuric acid converts it into 

 gum (359). Strong nitric acid produces a very re- 

 markable effect on lignin, and changes it into gun- 

 cotton, or xyloidine. In this action the lignin is 

 partially decomposed, and a portion of its oxygen 

 and hydrogen, in those proportions which would form 

 water, is replaced by some of the oxygen and nitro- 

 gen of the nitric acid. 



323. Gun-cotton is best formed by steeping pure 

 clean cotton wool, quite free from all oily matters, 

 either in very strong nitric acid, or in a mixture of 

 nitric and sulphuric acids ; the addition of the latter 

 is merely made for the purpose of rendering the nitric 

 acid stronger by extracting the water which it con- 

 tains. The cotton increases considerably in weight, 

 and when well washed and dried is found to be highly 

 explosive. It detonates at a heat a very little above 

 that of boiling water, with a bright flash, and is wholly 

 converted into carbonic acid, nitrogen, steam, &c. 



324. Woody fibre has a strong affinity for various 

 coloring matters, and also for some particular metallic 

 oxides, especially alumina, and the oxides of iron and 

 tin ; solutions of these substances are consequently 

 much used by dyers. The cotton to be dyed is first 

 impregnated with the mordant, as these substances 



