CASEIN ADHESIVES AND PUTTIES. 87 



The ammonia can of course be replaced by caustic potash, 

 caustic soda or any other alkali, but the presence of such 

 alkalies makes the glue more sensitive to moisture. 



POWDERED CASEIN GLUE. 



Dried, purified casein, 15 to 20 parts by weight, is ground 

 to fine meal in a pulveriser, and then incorporated, in a sift- 

 ing and mixing machine, with 1 to 4 parts of ground borax 

 or 2 to 8 parts of sodium bicarbonate, great care being be- 

 stowed on proper mixing. 



CASEIN AND BORAX GLUE. 



This is a solution of casein in a saturated solution of 

 borax. It has a transparent, gelatinous appearance, and 

 when dried forms a yellowish-white, somewhat brittle 

 mass, which is readily soluble in water, has high adhesive 

 properties and is suitable for cabinetmakers' use. It is 

 prepared by setting milk to curdle in a warm place, the 

 completeness of the operation being tested with hydrochloric 

 acid, 1 per cent, of which is added to the milk if the test 

 indicates that casein still remains in solution. The purifi- 

 cation and drying of the casein are performed in the manner 

 already described at the beginning of the present chapter. 

 For use the necessary quantity is placed in a suitable vessel 

 and mixed with levigated chalk, slaked lime, water-glass and 

 borax solution, an excellent adhesive being thus obtained. 



According to another report, this product is prepared as 

 follows. Milk is heated with a little tartaric acid, or when 

 large quantities are to be produced, is curdled in the 

 ordinary way as for cheesemaking. The resulting curd, in 

 a still moist condition, is sprinkled with a solution of 6 parts 

 of borax in 100 parts of water, and gently warmed and 

 stirred, the casein being thereby dissolved. The clear solu- 

 tion is a strong adhesive, cheap and durable, and can be 



