CASEIN ADHESIVES AND PUTTIES. 81 



afterwards warmed to make it curdle. To test whether all 

 the casein has been precipitated by the lactic acid of the 

 milk, a sample of the separated liquid is treated with a little 

 hydrochloric acid ; if a precipitate is formed there is still 

 some casein in solution, and this should be thrown down by 

 an addition of 1 per cent, of hydrochloric acid, without wait- 

 ing any longer for it to curdle. The curd is next pressed and 

 washed with soft water until the washings are free from all 

 trace of acid. To remove the final particles of fat the curd 

 is boiled up with water and spread on a filter cloth. 



When dry the curd is pressed and dried, first at a mod- 

 erate temperature, then with an increased application of heat, 

 and finally in a partial vacuum if necessary. In this way it 

 can be obtained either in the form of fine granules or as a 

 horny shrunken mass. In either case it will keep indefinitely, 

 but is liable to insect ravages, and especially to those of 

 larvae. 



CASEIN GLUE. 



" Casein glue is prepared by dissolving fat-free casein in a 

 saturated solution of borax, the resulting concentrated solution 

 having strong adhesive properties and finding extensive em- 

 ployment as a substitute for glue and gum arabic," says the 

 Revue des Produits Chimiques. 



The borax solution is prepared by dissolving one part of 

 borax in 12 parts of cold water, the casein being then added, 

 little by little. Casein powder is a mixture of 6 parts of 

 casein and one part of chalk, both in a powdered condition. 

 The mixture must be stored in a dry place, and shaken up with 

 cold or luke-warm water for use. To prepare casein cement, 

 curdled milk is triturated in a mill and with successive addi- 

 tions of slaked lime until a compact mass is formed. This 

 must be used almost immediately since it hardens very quickly. 

 Casein dissolved by a solution of carbonate potash or soda also 



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