112 L. C. CRAIG, W. KÖNIGSBERG, A. STRACHER, T. P. KING 

 diffuse through 20/32 Visking. Insulin is well known to aggregate at the 

 higher pH values. 



The A chain of insulin prepared by performic acid oxidation and purified 

 by CCD did not give a straight line in the dialysis study at any pH, and 

 scarcely passes the membrane above pH 7. It is apparently completely in 

 the extended form with a high optical activity. On the other hand, the B 

 chain gave a fairly ideal curve much like the purified insulin of Fig. 4 except 

 that it diffused through the membrane at a faster rate. 



Very early in the study with proteins, it was discovered that salt in the 

 solution had a retarding effect on the rate of dialysis. As an example, escape 

 curves at 25° and 20/32 Visking with ribonuclease in solutions of different 

 sodium chloride concentrations are shown in Fig. 5. In each case a break 

 in the curve was noted, but at a different point on the curve for each salt 

 concentration. Studies at 40° showed a faster overall escape rate but similar 

 breaks in the curve and were otherwise comparable. 



Hours 



Fig. 5. Escape rate curves of ribonuclease in aqueous solutions with various amounts 

 of sodium chloride. 



If the 50% time is plotted against ionic strength the curve shown in Fig. 6 

 is obtained. When magnesium sulfate was used one-fourth the molar con- 

 centration was found to have the same quantitative effect as sodium chloride. 

 Thus the ionic strength of the solution seems to be important rather than 

 the specific ion involved. 



An attempt was made to isolate the faster diffusing protein before the 

 break for a run with no salt and also the part emerging after the break. 



