ELECTROLYSIS 177 



protein is insoluble, while the combined protein is soluble. Con- 

 sider the electrolysis of a compound of such a protein with a base. 



The anion 



rl 



I 



R.N" 

 I 

 OH 



will migrate to the anode, and after neutralizing any excess of 

 base which may be present (since the ion, obviously, must contain 

 N.HOC groups and therefore, like the entire molecule, is am- 

 photeric) must eventually, when the film in immediate contact with 

 the electrode has become saturated with protein, be precipitated 



as the uncombined and therefore insoluble protein. The case is 



++ 

 very different with the cation R.CONa, for this, on arriving at 



the cathode, will bring it an excess of base and the cathode region 

 must become alkaline and, therefore, free protein cannot be pre- 

 cipitated there. Similarly, in the electrolysis of a salt of such a 

 protein with an acid the uncombined protein must be precipi- 

 tated at the cathode, but not at the anode. If the protein is 

 of such a type that the free protein is soluble, for example ovo- 

 mucoid, I have observed that no deposition of protein occurs at 

 either electrode, but only the evolution of gas, presumably hydro- 

 gen at the cathode and oxygen at the anode. That under such 

 conditions the protein nevertheless migrates to both electrodes has 

 been shown by Stirling and Brito (36) and by Howell (11). 



If a direct current of about one milliampere be passed through 

 a solution of potassium caseinate, which is neutral to litmus, 

 gas may be observed to be evolved at both electrodes, but a firm 

 white spongy precipitate is deposited upon the anode, the cellu- 

 lar texture of which is attributable to entangled bubbles of gas, 

 presumably oxygen (29). 



A quantity of this precipitate was collected. The anode con- 

 sisted of a spiral of platinum wire some 9 cm. long. This wire, 

 when coated with the precipitate, was well washed in a stream 

 of distilled water, and the precipitate was then scraped off into 

 99.8 per cent alcohol. The precipitate which was thus collected 

 under alcohol was washed with alcohol and ether and dried at 

 30 degrees over sulphuric acid for 48 hours. 



The precipitate proved to be uncombined (base free) casein. 



