SUNDBY APPLICATIONS OF CASEIN. 155 



The elasticity and resisting properties of the mixture of 

 casein and neutral wool fat render this composition specially 

 adapted for grounding artists' canvas. 



Another composition, suitable for photographers' back- 

 grounds, is obtained by mixing cement or diatomaceous earth 

 with casein solution. In this case also the durability of the 

 priming can be increased by spraying it with a dilute 

 solution of formaldehyde. 



In the case of canvas for other decorative purposes, the 

 power of resisting the action of the weather is a prominent 

 necessity. The priming for this purpose may be prepared 

 by stirring 18 parts of chalk and 2-J- of earthy pigment to a 

 pap with water. Ten to 14 parts of casein that have been 

 treated with alkali are next stirred in, and the whole is 

 diluted with another 10 parts of water. 



For priming canvas out of doors the following method 

 is recommended : 10 parts of finely powdered casein soluble 

 in water are intimately mixed with 10 parts of slaked lime 

 and 90 of levigated chalk, and diluted with water to workable 



consistency. 



SOLIDIFYING MINERAL OIL. 



Casein and formaldehyde play a- special part in the solidi- 

 fication of petroleum and other mineral oils. The oil is 

 treated with dissolved casein or an alkali salt of same, 

 e.g., sodium caseate. According to Helbing & Passmore's 

 Patent Specification, the resulting compound is hardened 

 with formaldehyde, and is then insoluble in water ; it has no 

 melting-point, but the petroleum can be recovered by dis- 

 tillation. The product is similar in colour to the petroleum 

 used, but is less transparent. 



USES OF CASEIN IN PHOTOGRAPHY. 



In connection with the employment of casein as a medium 

 for photographic purposes, Dr. Otto Buss expresses himself 

 in the following terms : 



