158 CASEIN. 



ical means. These experiments were also given up; and 

 although it is not asserted that the use of alkaline solutions 

 of casein in one or other of these directions is an impos- 

 sible matter, it would seem that some technical device of a 

 very different character to the usual methods of working 

 will have to be adopted to ensure success ; at any rate, the 

 writer does not at present think it likely that a normal 

 practical method will be discovered. 



An explanation of the peculiar behaviour recorded above 

 is afforded by the chemical conduct of casein. The sub- 

 stance may be regarded both as a basic and a dibasic acid, 

 since it is insoluble in water, alcohol, ether, acetone and other 

 known solvents, whilst it furnishes salts both with metals 

 -and acids. The alkali caseates are readily soluble in water, 

 whilst the compounds with the heavy metals, such as iron, 

 copper, silver, etc., are thrown down as insoluble, amorphous, 

 flocculent precipitates from the solutions of the alkali salts. 



The dibasicity of casein is revealed by the fact that it 

 dissolves to an acid solution when stirred up with water 

 and carefully treated with a dissolved alkali, whilst, after 

 neutrality is reached, a further quantity of alkali can be 

 added before the same appears in excess, that is to say 

 before the appearance of an alkaline reaction can be detected. 



The alkali caseate will therefore act as a dibasic salt in 

 presence of silver nitrate, normally with the formation of 

 silver caseate (presumably containing two atoms of silver) 

 and alkali nitrate ; and this will invariably occur, no matter 

 in what manner the casein and alkali are brought into 

 solution. Silver caseate, however, is by far inferior in sta- 

 bility to silver albuminate, inasmuch as the silver caseate 

 image is soluble in hypo. 



On the other hand, casein dissolves in dilute acids, from 

 which solution it can be reprecipitated by neutralisation 

 with alkali, without decomposition. The same precipitate 



