The Typical Cellulose and the Cellulose Group 45 



which on evaporation leave the nitrate as a glass-clear film of 

 considerable elasticity and tenacity. The products, both in 

 solution and in the form of films, are applied in numerous 

 directions, chiefly in connection with photography. 



It is important to observe that these nitrates preserve in a 

 remarkable degree the essential physical properties of the 

 original cellulose, which will be most obvious by comparison 

 of the above products with those obtainable with the cellulose 

 regenerated from solution as thiocarbonate. But this is still 

 better illustrated by the processes of converting the nitrates 

 into a continuous thread, available as a textile material. This 

 product is known as artificial silk. Various inventors have 

 devised means for 'spinning' solutions of cellulose nitrates 

 into thread, one of which may be briefly described as having 

 reduced the operation to one of extreme mechanical simplicity. 

 It is essential to the production of a thread of sufficient tensile 

 strength as directly obtained to stand the strain of the 

 drawing process, that the solutions employed contain a certain 

 minimum proportion of the dissolved nitrate. Dr. Lehner, of 

 Zurich, 1 after investigating the various problems involved, found 

 that, whereas ordinary collodion containing such a proportion 

 of the pyroxylin (10-12 p.ct.) in solution is unworkable under 

 the prescribed conditions, the adding of dilute sulphuric acid 

 causes a molecular change, and gives the solution the requisite 

 fluidity. With such a solution the conversion into thread is 

 effected as follows : The solution, carefully filtered and free 

 from all bubbles, is caused to flow by way of glass tubes to a 

 lower level, where it is delivered through a much narrowed 

 opening with a steady constant flow. The shorter limb ending 

 in this fine orifice is contained in a glass cell filled with water. 



1 See original German patent D.P. 58508/1890. The earlier pro- 

 cesses of De Chardonnet (1885) and du Vivier (1889) must also be men- 

 tioned. See D.P. 38368/1885 and 46125/1888. Also Br.Pat. 2570/1889. 



