246 ANIMAL PROTEINS 



involving a disadvantageous lyotrope influence. There is 

 another objection to oxidizing agents also ; whilst their 

 bleaching action on the pigments is undoubted, some of 

 them have also a special action upon the gelatine itself 

 which is in reality akin to tanning, and may indeed involve 

 an insolubilization of the gelatine. Thus, chlorine gas 

 (\vhich Meunier patented for tanning) has been used for 

 bleaching gelatine, but the conditions of success have not 

 vet been thoroughly elucidated, and it is problematical 

 indeed whether the process is consistent with best results. 

 Hypochlorites and bleaching powder have also a similar 

 action, which has been utilized with some success in 

 practice. Rideal suggests that a suitable concentration for 

 these reagents is i : 2000, and emphasizes the care necessary. 

 An advantage of all these chlorinations is the formation of 

 the strongly antiseptic chloramines, which preserve the 

 gelatine from putrefaction. Ozone has also been tried as an 

 oxidation bleach for gelatine, but not successfully, partly 

 on account of difficulties in controlling the quantity used. 

 Peroxide of soda has also been used, but it is not only 

 alkaline, but liable to contain sodium hydrate and carbonate 

 as impurities, and this involves neutralization either before 

 use or in the gelatine sol, and the consequent presence of 

 sodium salts in the finished article. Peroxide of calcium is 

 open to the same objections, except that calcium is more 

 easily removed from the sol than sodium. Rideal's suggestion 

 for removing this lime, viz. precipitation by a current of 

 carbonic acid, merits attention in this and in other directions 

 also. Rideal also states that in the case of an acid bone 

 gelatine, a good peroxide of lime is almost an ideal reagent 

 for bleaching, inasmuch as " the lime carries down phosphate, 

 several impurities and colouring matters." It thus acts 

 as bleach, as neutralizing agent, and as precipitant, and the 

 precipitate itself is a strong adsorbent. On account of its 

 freedom from bases, and because its residue is simply water, 

 peroxide of hydrogen has been found of great service in 

 practice, and in most factories it has shown itself superior 

 not only to the other peroxides, but also to all other oxidizing 



