HANDBOOK FOR BIO-CHEMICAL LABORATORY. 13 



solution. On shaking the precipitate it dissolves in the com- 

 mon salt solution, yielding a cloudy liquid ; place the solution 

 in a separatory funnel and shake with an equal volume of 

 ether. It will remain clear or nearly so. Draw off the 

 watery solution and allow it to stand until the next day, 

 when a cloudiness will have appeared; this is settled byre- 

 shaking again with ether. Draw off the watery liquid again, 

 measure it, and dilute with 10 vols. of water. The very fine 

 precipitate produced is filtered off the following day, washed 

 with water and then with alcohol. To further purify the 

 substance thus obtained place the precipitate in a flask, boil 

 with absolute alcohol on the water-bath, filter, wash with alco- 

 hol, then with ether, and lastly subdivide the mass in a flat 

 dish and allow to dry over sulphuric acid or in a vacuum. 

 (Salkowski.) 



Properties. Vitellin is insoluble in water, but soluble in 

 dilute neutral salt solutions. It is soluble in hydrochloric acid 

 of 1 p.m. and in very dilute solutions of alkalies or alkali 

 carbonates. The coagulation temperature for the solution 

 containing NaCl lies between 70 and 75 C. It yields nuclein 

 when digested with pepsin and hydrochloric acid. Vitellin 

 obtained as above should contain only 0.95$ phosphorus. 



Casein. 



Preparation. 200 c.c. fresh milk are diluted with 800 c.c. 

 water and treated with acetic acid so that the dilute milk con- 

 tains 0.75-1 p.m. acetic acid. (Hydrocloric acid may also be 

 used.) The casein hereby precipitated is quickly washed with 

 water by decantation and rubbed with water in a mortar so that 

 it is as fine as possible. Dissolve it with the least possible quan- 

 tity of a 0.1$ caustic-soda or ammonia solution, continually 

 stirring, and taking care that the liquid does not became alka- 

 line but neutral. The milk-white liquid is filtered through 

 several folds of filter-paper, when it will become water-clear 



