NUTRITIVE PRINCIPLES OF PLANTS. 251 
casein, as it is obtained from beans, peas, and lentils, is allowed 
to stand for twenty-four hours, at a temperature of from 60° to 
70° Fahr., a gelatinous precipitate is formed much resembling 
caseum. The supernatant liquid is of a greenish yellow colour, 
and has a decidedly acid reaction ; a little gas is at the same 
time seen to escape. This acid is the lactic; for when it is eva- 
porated with oxide of zinc, crystals are formed, possessing the 
characteristic insolubility of the lactate of zinc. 
The coagulum is a lactate of vegetable casein; it has an acid 
reaction, and cannot be obtained otherwise by the longest wash- 
ing with water or alcohol. The lactate of vegetable casein is 
very soluble in ammonia and the alkalies; alcohol and ether 
extract from it a green fatty matter. When an alkaline solution 
of vegetable casein is kept boiling for some time with an excess 
of potash, the addition of dilute sulphuric acid causes a precipi- 
tate, and the escape of sulphuretted hydrogen. Vegetable casein 
conducts itself with the salts of the earths and metals, exactly 
like the casein of milk. 
The sulphate of magnesia, the acetate and other salts of lime, 
are not precipitated by an aqueous solution of pure animal casein, 
when cold; but the slightest heat causes immediate coagulation. 
Vegetable casein has the same properties; when it is dried and 
heated to redness, white alkaline ashes are obtained, which con- 
‘tain a great deal of potash, part of it united to phosphoric acid. 
The salts contained in vegetable casein, which are insoluble in 
water, are phosphates of magnesia, lime and iron, as in the milk 
of animals. It is impossible to obtain this casein soluble in water 
by itself, by adding carbonate of lime or barytes to the sulphate, 
as it appears to enter into insoluble combinations with these two 
earths much more readily than animal casein. 
The soluble animal casein, obtained according to the method 
described by Braconnot, is never free from some foreign matter ; 
it possesses also in an equal degree the power of forming com- 
binations: its solutions cannot be warmed with carbonate of lime 
or barytes without being decomposed, forming perfectly insolu- 
ble compounds, which become hard as a stone in the air. 
The animal casein prepared by Berzelius contained 6°5 per 
cent of foreign substances, such as phosphate of lime, magnesia, 
iron, and free lime, so that, strictly speaking, we are as little 
acquainted with a pure soluble animal as we are with a pure 
vegetable casein, free from bases or acids. In a word, it is im- 
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