140 THE CARBOHYDRATES 



outer .surface may be deiiitrated by treatment with alkali, 

 whereby it is rendered non-flammable. Artificial gutta-percha 

 is obtained by allowing an acetone solution of tetra-acetyl 

 cellulose to evaporate. 



Celluloid is produced by mixing the tri- and tetra-nitrates, 

 as employed for collodion, with camphor. 



Artificial Silks. — These are produced in a variety of ways 

 by precipitating some form of cellulose from solution. The 

 first artificial silk was prepared by Chardonnet, who obtained 

 it by forcing collodion through fine nozzles ; the thin stream 

 of nitrocellulose solution on coming in contact with the air 

 solidifies to a thread by the rapid evaporation of the solvent. 

 To render it non-flammable the thread is denitrated by treat- 

 ment with ammonium sulphide. 



A second process for preparing artificial silk consists in 

 dissolving bleached mercerized cotton (see p. 131) in cupram- 

 monium solution. A fine stream of this solution is then run 

 into a dilute sulphuric acid, whereby a continuous thread of 

 cellulose is at once precipitated. 



Viscose is obtained by acting on finely divided cellulose 

 with soda and treating the resulting substances with carbon 

 disulphide, whereby a cellulose thio-carbonate is produced ; 

 this substance on exposure to air decomposes spontaneously 

 into cellulose alkali and carbon disulphide. Viscose solutions 

 are employed for sizing paper, in the manufacture of wall- 

 papers and for the production of thin threads for spinning by 

 forcing the solution through fine nozzles and allowing the 

 emerging stream to coagulate in the air. 



Mixed with metallic dust and colouring matters, viscose 

 can be converted into an artificial leather, and may also be 

 employed for rendering canvas waterproof and for making 

 cinematograph films, etc. 



Viscoid, which is congealed viscose, is a hard mass obtained 

 by mixing viscose with various substances and allowing the 

 mixture to decompose spontaneously and harden ; it is used 

 for mouldings, cornices, statuettes, etc.* 



Solid Spirit. — The substance sold under this name is ob- 

 tained by pouring a solution of cellulose acetate in glacial 



*See Bersch : " Cellulose, Cellulose Products and Artificial Rubber," Phila- 

 delphia, 1904. 



