INDUSTRIAL USES 237 



resulting substance may be made to have any degree of elas- 

 ticity, according to the materials which are mixed with it. 

 It forms a more or less satisfactory substitute for rubber and 

 possesses a high electric resistance. Though not explosive, it 

 is inflammable, but to do away with this inconvenience the 

 outer surface may be denitrated 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 

 sohdifies 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. 209) in cupram- 

 monia 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. 



A third process is that in which viscose solution is forced 

 through fine nozzles, the emerging streams being coagulated 

 either by hot air or by a bath of ammonium chloride. The 

 fine threads which result can be spun like silk. Cellulose 

 acetate also is used for this purpose. 



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 alkaH and carbon disulphide. Viscose solutions 

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

 papers. 



Mixed with metallic dust and colouring matters, viscose 

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



