80 



5 Lumiere & Seyewitz, Bull. Soc. Chim., iii., 33, 1032 (1905). ' Sur la 

 composition de la gelatine iinpregnee de bichromate de potassium insolubilis^e 

 par la lumiere et sur la theorie de cette insolubilisation.' 



■* Lumiere & Seyewitz, Bull. Soc. Chim., iii., 35, (376 (1906). 'Action des 

 alums et des sels d'alumines sur la gelatine.' 



* Lumiere & Seyewitz, Bull. Soc. Chim., iii., 35, 377 (1906). 'Sur le 

 ph^nomene de rinsolubilisation de la gelatine dans le developpement et en 

 particulier dans Femploi des revelateurs a I'acide pyrogallique.' 



"Lumiere & Seyewitz, Bull. Soc. Chim., iv., 1, 428 (1907) ' Siu' I'insolu- 

 bilisation de la gelatine par la quinoine.' 



' Lumiere & Seyewitz, Bull. Soc. Chim., iv., 3, 743 (1908). ' Sur les phenomenes 

 de la precipitation et de I'insolubilisation de la gelatine.' 



■* Procter, Transaction.^ of the Chemical Society, 105, 313 (1914). ' Equilibrium 

 of dilute hydrochloric acid and gelatin.' 



' Procter, British Association, First Report on Colloid Chemistry cnul its 

 Industrial Application, 24 (1917). ' Colloid Chemistry of Tanning.' 



i» Sheppard & ElKot, Brit. Jour. Phot., 65, 480 (1918). ' The Reticulation 

 of Gelatin.' 



" C. R. Smith, Jour. Am. Chem. Soc, 41, 149 (1919). ' Mutarotation in 

 gelatin and its significance in gelatinisation.' 



Gum. 



Gum is used in the gum bichromate process as the base of a pigment 

 process jiist as gelatin is used in the carbon process, but a very thin 

 layer of the colloid is used so no transfer is necessary. The gum is 

 made insoluble by exijosure to light after sensitisation with a 

 bichromate. Gum arable is generally used in this process. Starnes 

 states that better results are obtained by the use of gum Senegal. 



Starnes has made some experiments from which he concludes 

 that when bichromate is added to the gum it is at once rendered 

 less soluble. On exposure to hght it first becomes quite soluble and 

 then, on further exposure more and more insoluble. Thus in the 

 early stages of printing there is a reversal of the image. The 

 phenomenon has, however, not been investigated quantatively. 



Starnes, The Photographic Journal, 42, 287 (1918). 'The gum-bichromate 

 process with a now colloid.' 



COLLODION IN PHOTOGRAPHY. 



By H. W. Greenwood. Research Chemist to The Leto Photo Materials 



Co. (1905), Ltd. 



The use of collodion has been coincident with the rise and progress 

 of photograjihy — by collodion is here meant a solution of pyroxylin 

 in ether alcohol. 



Any discussion of the colloid chemistry of collodion apart from 

 other forms of nitro-cellulose is almost an impossibility, for although 

 a great volume of work has been done, only a very small part of this 

 may be claimed as appertaining solely to collodion. 



The role of collodion in photography is similar to that of gelatine. 

 It acts as a protective colloid, as a support, and also at times plays 

 a part in the actual reactions. The greatest difference between 

 collodion and gelatine is that collodion, except to a negligible degree, 

 does not act as a sensitiser. Its insolubility in water, comparative 



