100 HOW CROPS GEOW. 



(one to one and oue-lialf parts potash to 1000 parts of water), and the 

 liquid, after standing some days at rest, may be poured oflf 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 Kitthausen) 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 vegelaUe-fibrin nearly pure. 



Vegetable-fitrin is readily soluble ia hot alcohol, but 

 slightly so in cold alcohol. It does not at all dissolve in 

 water. It has no fibrous structure like animal fibrhi, 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 acid. 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 mUk 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, Jlfec?. Chem. Uh- 

 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. 

 Digitized by Microsoft® 



