56 THE GENERAL CHARACTERS OF THE PROTEINS 

 | 



If the sodium salt thus obtained be acidified it is reconverted into the 

 free acid and sodium chloride 



CH 3 . CH : NO . ONa + HC1 = CH 3 . CH : NO . OH + NaCl. 

 Such a solution has at first the electrolytic conductivity of the acid 

 pseudo-form + that of sodium chloride. After a time, however, the 

 pseudo-form gradually reverts to the true nitro-form, the conductivity 

 diminishes, and the solution attains finally the conductivity due to 

 sodium chloride alone. In a like manner the neutralisation of the 

 true nitro-body does not take place immediately, but there is a certain 

 latent period. The higher the temperature the shorter is this period. 

 Similarly certain pseudo-bases have been shown to exist, and 

 both are characterised by this latent period of neutralisation. The 

 conductivity changes, moreover, when neutralisation takes place, are 

 characterised by a high temperature coefficient, owing to the influence 

 of the increased temperature on the rate of change. 



Neither the latent period of neutralisation nor the high tempera- 

 ture coefficient for the conductivity has been observed by Hardy in 

 his investigations on the serum-globulin, and he comes to the conclu- 

 sion that the hypothesis of Cohnheim that proteins act as pseudo-acids 

 and pseudo-bases is not justified by experimental facts. Similar 

 conclusions have also been arrived at by a different experimental 

 method by von Rhorer. 



In concluding this section, emphasis must be laid upon the 

 anomalous behaviour in many respects of the proteins on treatment 

 with acids and bases. This behaviour is probably to be ascribed to 

 their capacity as colloids to adsorb inorganic substances, to which 

 reference has been already made in the introduction. This fact 

 renders it often impossible to discriminate between physical adsorption 

 and chemical combination, and for this reason some of the conclusions 

 recorded above must be accepted with reserve. 



SECTION XVII. THE PRECIPITATION OF PROTEINS BY SALTS 

 OF THE HEAVY METALS. 



It has already been mentioned that the addition of salts of the 

 heavy metals, such as those of copper, mercury and lead, to protein 

 solutions produce precipitates. Numerous attempts have been made 

 to determine the composition of such precipitates and to isolate 

 definite protein salts of the heavy metals. There is a large literature 

 on the subject, and the various investigators have arrived at results 

 which are by no means concordant. The precipitates, which have 

 received the largest amount of investigation, are those produced by 

 the addition of copper salts. Certain of the products isolated have 

 a relatively large copper content, as the following analyses, due to 

 Ritthausen, of vegetable protein precipitates show : 



CuO. Ash. 



" Gluten-caseinogen " from wheat 16-97 



Legumin from peas I5'6i i'2i 



from broad beans 14-10 3-05 



,, from oats 13 '53 



Conglutin from lupines i3'38-ii-6o o 43-2'i6 



The copper precipitate obtained from milk caseinogen also shows a 

 high copper content 127 to 13*6 percent., according to the analyses 

 of Ritthausen and Pott. 



Very widely differing results have been obtained by analyses of 



