362 CHEMICAL DISCOVERY AND INVENTION 



out so long ago as 1890, the use of artificial silk as a weaving 

 material has not become commercially important till within the 

 last few years. 



As a matter of history the first process employed was based 

 on the already long known properties of the nitrocelluloses. 

 (See also Explosives.) When cotton is immersed in a mixture of 

 nitric and sulphuric acids with a little water, a mixture of 

 cellulose nitrates is formed which retains the form of the cotton, 

 but differs from it in being soluble in a mixture of alcohol and 

 ether. The resulting viscous solution when evaporated leaves a 

 colourless film insoluble in water, the collodion of the photo- 

 grapher. If such a viscous solution made of suitable strength is 

 forced through minute holes or fine glass jets either into water 

 or into a warm atmosphere, the alcohol and ether are removed 

 and fine threads are obtained which may be wound on a spool 

 much in the same way as in winding silk from the cocoon. The 

 fibre thus produced, however, has the great disadvantage of 

 being dangerously inflammable. It was therefore reduced by 

 passing it through a solution of ammonium sulphide by which 

 the nitrate groups it contains are removed and a substance 

 having the composition of cellulose is reproduced. This process 

 has survived only to a limited extent as a manufacturing process, 

 but by the employment of other and cheaper solvents artificial 

 silk is manufactured and finds application in a variety of ways. 



The cuprammonium process based on the employment of the 

 solution of copper oxide in ammonia already described is one of 

 these. The threads of cellulose solution are forced through jets 

 into dilute sulphuric acid which removes the copper and repro- 

 duces the solid cellulose. But another and more successful 

 process employs the viscose reaction of Messrs. Cross and Bevan 

 which has already been explained. 



Yet another process based on the formation of a cellulose 

 acetate is employed for the production of threads, but more 

 particularly, films of cellulose for use in the cinematograph and 

 for other purposes. 



It is obvious, from the brief description which has been given, 

 that the threads of cellulose thus produced and which when 

 spun form artificial silk, are entirely devoid of structure. Instead 

 of being hollow, as are natural fibres, they are solid cylindrical 

 threads, and as such present in the woven form an appearance 

 different from that of cotton or linen. The lustre of artificial silk 



