82 



greatei- or lesser degree, and that this dcnitration explains the anomalies 

 that are so frequently met with in connection with the viscosity of 

 collodions, and also with the behaviour of different films from one 

 and the same solution. This decomposition is capable of acceleration 

 not only by temperature but by many chemical agents ; and also, 

 probably takes place spontaneously at ordinary temperatures. The 

 action of bromides in causing denitration is well known. One aspect 

 of this jDhenomena is its importance in relation to the question of 

 the keeping properties of collodion plates and papers, and of the 

 permanence of the photographic image, whether negative or positive 

 after the usual processes of development, fixation, &c., and in this 

 direction much further investigation is called for. 



CELLULOSE ESTERS. 



By Foster Spboxton, B.Sc, F.I.C, Chief Chemist to the British 



Xylonite Co., Ltd. 



The technical problems which arise in any colloid industry naturally 

 depend on the uses to which the finished material is put, and in view 

 of the varied nature of the applications of such products as leather, 

 glue, starch, explosives, and colloidal metals, it is not surprising 

 that each industry is concerned with a somewhat different aspect of 

 the chemistry and physics of highly disperse matter. 



The industry of the cellulose esters has for its principal object 

 the manufacture of a material of valuable mechanical properties. 

 Its colour, transparency, surface, &c., though of great importance, 

 would be of Uttle moment if the material did not possess elasticity, 

 tensile strength, and toughness at ordinary temperatures, and plasticity 

 at higher temperatures. The object of the industry is the provision 

 of a material combining these properties -without prejudice to its 

 adaptability for artistic and imitative effects. 



It must be admitted that in the case of celluloid a high standard 

 of technical excellence has been reached without the assistance of 

 theories of the nature of the plastic material. The reproduction of 

 material possessing the desired properties is accomplished only by 

 strict control of the raw and semi-manufactured material, and close 

 adherence to the conditions ascertained by experience. 



A brief account of the manufacture of celluloid will be found in 

 Thorpe's " Dictionary of Applied Chemistry, "^ to which the reader 

 is referred. The manufacture of plastic materials from acetyl cellulose 

 is described by Worden.- The colloidal problems encountered in 

 the two manufactures are very similar except in the case of the 

 preparation of the starting materials, nitro-ceUulose and acetyl 

 cellulose. These will be considered separately. 



Nitro- cellulose is made, as is well known, by the action of a mixture 

 of sulphuric and nitric acids on cellulose, usually in the form either 

 of cotton or paper. The two phases, solid cellulose and liquid acid 

 mixture, persist throughout. It has been shown by Cross, Bevan, 

 and Jenks, and by Hake and Lewis,* that there is an intermediate 

 formation of sulphuric esters of cellulose, which are gradually converted 



