CHAPTER VII 



THE COMPOUNDS OF THE PROTEINS (Continued) 



1. Compounds with the Heavy Metals. — From what has 

 been said in the previous chapter concerning the mechanism of the 

 precipitation and coagulation of proteins by salts, it will be clear 

 that the percentage of a heavy metal which is bound by protein 

 must depend very intimately upon the mode of preparation of the 

 compound. For instance, in the presence of silver nitrate under 

 conditions involving moderate hydration (e.g., a fairly high con- 

 centration of the silver nitrate or the presence of some other 

 dehydrating agent), or in alkaline solution, the following reaction 

 may occur : jj 



I 

 H2N.R.C0Na.N.R.C00H + 2 AgNOg 



I Ag 



OH I 



= HzN.R.COAg.N.R.COOH + NaNOs 

 I 

 NO3 



in an acid medium, or under conditions involving less hydration, 

 this compound could not exist and the reaction 



Ag 

 I 

 H2N.R.C0Ag.N.R.C00H + H2O 



I H 



NO3 I 



->H2N.R.C0Ag.N.R.C00H+ AgOH 

 I 

 NO3 



must occur. In a still more acid medium the silver would be 

 altogether abstracted from this compound, while in a fairly 

 strongly alkahne medium the compound 



H 



I 

 HaN.R.COAg.N.R.COOH 

 I 

 OH 



137 



