124 CASEIN. 



of formaldehyde is of 1 to 2 per cent, strength. Formal- 

 dehyde bisulphite is prepared by mixing 8 parts by weight 

 of 40 per cent, formaldehyde with 10 of sodium bisulphite 

 of 30 B. strength. The hexamethylenamine is obtained 

 from 8 parts of formaldehyde and 10 of concentrated 

 ammonia. 



CASEIN FOR MERCERISED CREPE. 



According to a German patent process, the fabric is 

 printed with casein or albumen, steamed to produce co- 

 agulation, passed through a concentrated solution of caustic 

 soda (30 to 35 B.), squeezed between rollers to express 

 the superfluous lye, hung up for a time to prevent an un- 

 due rise of temperature in consequence of the mercerisation 

 process, then acidified with dilute hydrochloric acid, washed 

 and dried on a tenting frame. 



FIXING ZINC WHITE ON COTTON WITH FORMALDEHYDE. 



The use of formaldehyde or formalin in cotton printing 

 is based on its property of coagulating casein, albuminoids, 

 glue, etc., and rendering them insoluble. Thus, in printing 

 metallic powders and pigments on cotton fabrics, use can 

 be made of a compound of casein or gelatine and formalin 

 (Schering). Moreover, formalin can be employed with 

 advantage for fixing zinc oxide, printed in a medium of 

 casein and borax on thin, transparent fabrics or on mercer- 

 ised cotton goods. The fabric remains soft, and the dull 

 zinc white produces a favourable effect in contrast with the 

 glossy ground ; and it can also be toned to any desired shade 

 by the addition of pigments. At the same time it appears 

 that the action of the formaldehyde on the casein is more 

 rapid and thorough in an atmosphere of hot steam than in 

 ordinary air. The fabric is therefore put through a Mather 

 and Platt machine, in which the formaldehyde is vaporised 



