154 CASEIN. 



started, 5 parts of casein powder are run in by degrees, 

 and in this way a uniform solution is obtained. It will not 

 do to add too much powder at a time or to put the casein 

 into the trough first and then the water, or a lumpy pap will 

 be obtained instead of a thin solution. The warming of the 

 trough throughout the operation will prevent the solution 

 thickening too soon. 



This solution is next applied evenly to the surface of the 

 stretched canvas. When the coating is dry the next step is- 

 to apply the priming composition a mixture of neutral 

 wool fat, dissolved casein and the finest levigated chalk or 

 lithopone. Drying oils and driers may also be added in 

 moderate amount. 



The neutral wool fat, which exudes from the glands in the 

 skin of the sheep, and constitutes the grease permeating the 

 wool, is met with in a purified state in commerce, as lanolin, 

 It differs from vegetable and animal fats inasmuch as the con- 

 tained fatty acids are not combined with glycerine, but with 

 cholesterin and the so-called fatty alcohols. Thanks to this 

 constitution the fat is better able to stand the influence of 

 warmth, air and light than the other fats of animal or vegetable 

 origin. It remains perfectly sound even after prolonged ex- 

 posure to atmospheric influences, and unlike the glycerine fats 

 it shows no increase of acidity, no rancidity. Another conse- 

 quence of the peculiar composition of neutral wool fat is its 

 high resistance to the action of alkalies and caustic alkaline 

 earths, so that, under ordinary conditions, it is unsaponifiable. 

 The neutral wool fats are miscible with water, and are able to 

 absorb and permanently retain up to twice their own quantity 

 of water a valuable property when the incorporation of 

 large quantities of water into a fatty mixture is in question. 

 As a rule the neutral wool fats are among the most stable 

 fats known, and their valuable qualities ensure them a pro- 

 gressively extending industrial future. 



