84 



in which case loss of weight/loss of vohime = 0. On a priori grounds, 

 therefore, any vahie for this ratio (which is the apparent specific gravity 

 of the alcohol and camphor lost) might be expected. It was found 

 in some careful experiments on a certain variety of celluloid in the 

 final stages of drying that the ratio varied only from 0-82 to 0-91, 

 the mean value for 28 samples being 0-87. This is the specific gravity 

 of a solution of camphor in alcohol containing 42 per cent, of camphor 

 by weight. Although these experiments do not prove that the 

 shrinkage in volume of celluloid while seasoning is exactly equal to 

 the volume of camphor and alcohol lost, they show that the difference, 

 if any, must be small. 



There is no more fascmating branch of the technology of cellulose 

 esters than the study of solvents. Hundreds of substances and mixtures 

 of substances are known which have more or less marked solvent 

 action on nitrocellulose or acetylcellulose, but the question of how to 

 make a fair comparison between one solvent and another has never 

 been completely worked out. The work was begun for nitrocellulose 

 by the late F. Baker ^ He came to the conclusion that the best 

 solvent of a particular sample of nitrocellulose was the solvent which 

 yielded the solution of lowest viscosity, and this is in agreement with 

 manufacturing experience. It may be pointed out, however, that 

 another method might be chosen, and that is to find the solvent 

 yielding solutions which wiU bear the greatest dilution with an 

 indifferent, miscible non-solvent, such as petroleum ether, before the 

 cellulose ester is precipitated. This method is also in line with the 

 technical valuation of solvents, and a rigorous comparison between 

 the two methods would be most interesting. Petroleum ether has been 

 suggested here as the indifferent liquid, because of the unexpected results 

 sometimes obtained when mixtures of liquids -act on cellulose esters. 

 It has been long known that ethyl alcohol and ether are, separately, 

 non-solvents of soluble nitro-cotton, but form a solvent when mixed. 

 This mixture was investigated by Baker^, and he concluded that the 

 solvent power was exerted by a complex formed by the combination 

 of ether and alcohol. This is a reasonable explanation of this par- 

 ticular case, but it does not explain the extraordinary effect sometimes 

 produced on solvent power by the additions of quite small amounts 

 of foreign substance. One instance which has long been known is 

 the solvent power imparted to methyl alcohol by the presence of 

 traces of acetone. A recent example of the technical appUcation of 

 the jDrinciple is Eng. Pats. 14,655 and 14,656", in which the addition 

 of small quantities of substances such as nitro-toluenes, formanihde, 

 &c., is employed to facilitate the solution of nitrocellulose in nitro- 

 glycerine. 



But, returning to the consideration of mixtures such as ether- 

 alcohol where each constituent is present in bulk, it would be of 

 interest to extend Baker's viscosity work on solvent power to such 

 mixtures, and find what proportions of the constituents produced the 

 best solvent mixture. Probably the records of such experiments exist, 

 but they do not appear to have been published. — Index 9a. The results 

 would be of value in a field somewhat remote from that of colloid 

 chemistry, in view of the recent work of Bramley and others on binary 



