32 THE ALBUMINS. 



salts, without loss of their characteristic properties or change iu 

 structure. The resulting precipitates are soluble as before. This 

 behavior toward neutral salts is not characteristic of albumins, 

 however, as every substance can, generally speaking, be withdrawn 

 from its solution by a second body, but owing to the great molec- 

 ular size of the albuminous molecule these bodies are thrown out 

 of solution more readily than others. 



The salts which are usually employed in the chemical laboratory 

 for the precipitation of the albumins are sodium chloride, sodium 

 sulphate, magnesium sulphate, and especially ammonium sulphate 

 and zinc sulphate. The two latter are especially important, as they 

 are universal precipitants, while the other salts and many others, 

 which have not been mentioned, will throw down only certain in- 

 dividual albumins. Generally speaking, the more highly differen- 

 tiated albumins can be precipitated by the least active salts, such as 

 sodium chloride and magnesium sulphate, while for the complete 

 precipitation of the less complex albumins (serum-albumin) and 

 certain albumoses ammonium sulphate or zinc sulphate is necessary. 

 The more complex the albumin the more readily it is precipitated, 

 so that with certain bodies, such as fibrinogen, casein, and other 

 nucleo-albumins complete saturation is not necessary. In their 

 behavior toward ammonium sulphate these bodies differ from the 

 less complex albumins in the fact that they require a smaller amount 

 of the salt for their precipitation. The simpler the structure, on 

 the other hand, the more salt is necessary. The deutero-albumoses, 

 which probably represent the least complex bodies, which still have 

 a distinct albuminous character, can only be precipitated by com- 

 plete saturation with ammonium or zinc sulphate, and with one of 

 their number it is necessary to carry out the saturation in acid 

 solution, while all other albumins and albumoses can be thrown 

 down from their neutral solutions. 



Magnesium sulphate occupies a position intermediate between 

 sodium chloride and ammonium sulphate, and readily precipitates 

 both globulins and primary albumoses. 



The behavior of the different albumins to neutral salts, and 

 notably to ammonium and zinc sulphate, is now largely utilized in 

 their differentiation from each other and the identification of the in- 

 dividual bodies. It has been ascertained that under certain con- 

 ditions each albumin has a definite lower and upper limit of precip- 

 itation, which for that body is quite constant i. e., for a given 

 volume of the solution a definite amount of salt is necessary, 

 beneath which no precipitation occurs the lower limit, and beyond 

 which no further precipitation takes place the upper limit. In 

 conformity with Hofmeister's suggestion this examination is now 

 generally conducted as follow r s : A series of test-tubes is prepared 

 which are successively charged with a constant number of c.c. (2) 

 of the albuminous solution (2 per cent.) and increasing amounts of 



