242 Biological Chemistry. 



process to be employed for characterization of proteins 

 obtained in the course of biological research. Of the 

 physical constants for the identification of individual pro- 

 teins, the solubilities in various solvents, the precipitability 

 by salts from aqueous solution, which has been already 

 discussed in detail (p. 238), and the optical rotation and 

 refractive index of the solutions, may also be employed. 

 Far more certain than the physical are certain chemical 

 constants which can be determined with relatively little 

 trouble. These are the following : 



(1) The Empirical Composition and the Sulphur 

 Content. With the exception of the basic protamines, 

 which yield large amounts of diamino-acids on hydrolysis, 

 and the histones, which also contain relatively large 

 amounts of nitrogen, and are also somewhat basic, though 

 less so than the protamines, there is not, as a rule, much 

 difference between the proteins as regards their carbon, 

 hydrogen, nitrogen, and oxygen content. The deter- 

 mination of the composition of a protein by means of the 

 ordinary combustion methods is, therefore, of little value 

 for their characterization, and for distinguishing between 

 proteins of different origins. Proteins yield, however, as 

 one of their hydrolysis products, cystine, which contains 

 sulphur; and as the amount of this element in a given 

 substance is determined very easily, and as there are wide 

 variations in the quantity of cystine which is yielded by 

 the hydrolysis of the different proteins, the sulphur esti- 

 mation affords a valuable method for characterization. 

 The amount of sulphur varies from less than 0'5 up to 

 5 per cent, in the different proteins, the higher value being 

 found in the case of hair, which yields a large amount of 

 cystine on hydrolysis. 



(2) The Nitrogen Distribution in the Hydrolysis Pro- 

 ducts. The " Haussmann Numbers" The hydrolysis 



