68 CHEMICAL STATICS 



in the union of the majority of proteins with inorganic acids and 

 bases. The active agents in accomphshing these unions are, 

 more probably, — COH.N— groups within the protein molecule. 



Whatever may be the method of union between inorganic sub- 

 stances and the proteins, however, there is now no longer any 

 doubt that it is of very general occurrence. The methods which 

 have been employed by various investigators to demonstrate 

 the existence of compounds of the proteins with inorganic sub- 

 stances are very diverse in nature, but they may be conveniently 

 classed as direct and indirect. The direct methods consist in the 

 precipitation of the (supposedly) unaltered compound by appro- 

 priate reagents (in the case of compounds such as those with the 

 heavy metals, which are insoluble in water, addition of a reagent 

 is of course unnecessary), followed by the elementary analysis 

 of the precipitate, or in the analysis of soluble compounds of 

 proteins with substances which, when uncombined, are insoluble 

 in water. The indirect methods may be variously designated: 

 the indirect method of precipitation, the method of electrical 

 conductivity, the cryoscopic method, the potentiometric method, 

 the method of catalysis, the indicator method and the method 

 of "masking" the physiological effects of inorganic substances 

 by the addition of proteins to their solutions. The results ob- 

 tained by these methods will be considered separately. 



2. The Direct Method of Demonstrating the Existence of 

 Protein Compounds by Precipitation or Coagulation. — ■ This, 

 which is the method most frequently employed, consists, usually, 

 in precipitating or coagulating the protein salt by the addition 

 of suitable reagents, the reagent which is most commonly em- 

 ployed being alcohol. 



The very important question immediately suggests itself, 

 whether or not the reagent which is employed for this purpose 

 precipitates the protein compound unaltered, as it exists in the 

 solution, or whether the compound is altered in the process of 

 precipitation. On the whole it may be said that too little atten- 

 tion has been given to this question by investigators who have 

 employed this method and that in consequence we possess very 

 little accurate information on the subject. 



It appears, however, that alcohol may be relied upon, at all 

 events within certain limits, to precipitate the salts of some 

 proteins with bases in an unaltered condition, that is, containing 



