148 



ISOELECTRIC POINTS OP PROTEINS 



placed a buffer solution of the same hydrogen ion concentration 

 extending to stop-cocks, AA, and conveniently introduced at DD by 

 creating a slight vacuum at C. Between the buffer solution (at A) 

 and the zinc sulfate in the non-polarizable electrodes a sodium chlo- 

 ride solution was placed to avoid the formation of insoluble zinc 

 salts. It was ascertained that the sodium chloride never met the 

 protein by testing for the faster moving chlorine ion in a drop of 

 solution pipetted from the arms of the U-tube. Once filled the level 

 of the solutions was adjusted through C. The stop-cocks BB were 

 then opened and, provided there was no diffusion, a 110 volt direct 



RdCl 



I\dCl 



ABBA 



IZnSOjCaCl I Buffer I Proleia I Buffer I T>Cl ISnSOj 

 Calophoresis ... 



Fig. 1. Apparatus for the determination of protein migration in an electric field. 



current was passed in series through the apparatus and a silver 

 coulometer. The deposit of silver in the latter recorded the flow of 

 current during cataphoresis. The drop in voltage across BB was 

 approximately 3 volts, but varied in different experiments with the 

 conductivity of the protein solution. Cataphoresis was carried on in 

 a thermostat at 25° ± 1°C. 



The Protein of the Potato. 



About 8 per cent of the solids of the potato is protein and about 

 4 per cent is ash." As a result, more than half the protein is dis- 



" The average of all the values given in Konig, J., Chemie der menschlichen 

 Nahrimgs-und Genussmittel, Berlin, 4th edition, 1903, i, 713. 



