54 THE NUCLEOALBUMINS. 



solutions, unlike the globulins, and differ from the alkali 

 albumins by being decomposed by the action of gastric juice 

 into an albumin, which is digested, and an indigestible 

 phosphorus compound called nuclein. The nucleoalbumins 

 may be considered, then, as compounds of a nuclein and an 

 albuminous substance. 



The nucleoalbumins are insoluble in water or dilute 

 acids. They can be dissolved in alkaline solutions. They 

 have the properties of dibasic acids, as is shown by the fact 

 that the solution in an alkali, where not too much of the 

 alkali has been used, has a slight acid reaction. The acid 

 reaction is also shown by their setting free the carbonic 

 acid of carbonates. The nucleoalbumins can be precipi- 

 tated from their alkaline solutions by acidifying. The 

 acid removes the alkali with which they are united and sets 

 the nucleoalbumin free as an insoluble substance. This 

 may be shown in the precipitation of the casein in milk. 



The nucleoalbumins are soluble in strong acetic acid 

 or an excess of hydrochloric acid, being at the same time 

 decomposed, nuclein being set free and the albumin being 

 converted into acid albumin. They are also decomposed 

 and coagulated by suspending the free nucleoalbumin in 

 water and boiling. 



In general, being compounds of the albuminous sub- 

 stances, the nucleoalbumins respond to the same tests. 



127. PKEPAKATION OF CASEIN. Dilute about 100 

 cubic centimeters of milk with 400 cubic centimeters of 

 water, and precipitate the casein until the liquid above 

 is nearly clear by adding acetic acid drop by drop, avoiding 

 an excess. Filter and wash with water. If fat-free sub- 

 stance is desired, it must be extracted in an extraction- 

 apparatus with ether. For many tests this is not neces- 

 sary. The casein can be to some degree purified by dis- 



