100 HOW CROPS GROW. 
(one to one and one-half parts potash to 1000 parts of water), and the 
liquid, after standing some days at rest, may be poured off from any 
residue of starch. On adding acetic acid in slight excess, the purified 
albuminoids are separated in the solid state. By extracting succes- 
sively with weak, with strong, and with absolute alcohol, a form of 
casein (gluten-casein of Ritthausen) remains undissolved, which is perhaps 
identical with the casein (legumin) of the pea. 
‘On evaporating the alcoholic solution to one-half, there separates, on 
cooling, a brownish-yellow mass. This, when treated with absolute al- 
cohol, leaves vegetable-fibrin nearly pure. 
Vegetable-fibrin is readily soluble in hot alcohol, but 
slightly so in cold alcohol. It does not at all dissolve in 
water. It has no fibrous structure like animal fibrin, but 
forms, when dry, a tough, horn-like mass. In composition 
it approaches animal-fibrin. 
Casein.— Animal casein is the peculiar ingredient of 
new cheese. It exists dissolved to the extent of 3 to 6 
per cent in fresh milk, unlike albumin is not coagulated 
by heat, but is coagulated by acids, by rennet, (the mem- 
‘brane of the calf’s stomach), and by heating to boiling 
with salts of lime and magnesia. 
Exp. 50.—Observe the coagulation of casein when milk is treated 
with a few drops of sulphuric acidy Test the curd with nitrate of 
mercury. | 
Exp, 51.—Boil milk with a little sulphate of magnesia (epsom salts) 
until it curdles,. 
When casein is. separated from milk by rennet, as in 
making cheese, it carries with it a considerable portion of 
the phosphates and other salts of the milk; these salts 
are not found in the casein precipitated by acids, being 
held in solution by the latter, 
The casein of milk coagulates spontaneously when it 
stands for some time. Casein has recently been detected 
in the brain of animals, (Hoppe-Seyler, Med. Chem. Un- 
ters., II.) 
Vegetable casein,—This substance is found in large pro- 
portion (17 to 19 per cent) in the pea and bean, and in- 
deed generally in the seeds of the so-called leguminous 
plants. It closely resembles milk-casein in all respects. 
