606 SUBSTRATE COXCEXTRATIOX AXD HYDROLYSIS 



found, however, that if the conductivity of the H+ and the total Cl~ were sub- 

 tracted from that of the solution the remaining values were within the limits of 

 error of the measurements. In other words, the conductivity due to the protein 

 ion itself is very small compared to that due to the excess chlorine ion (by excess 

 Cl~ is meant the difference between the total Cci- and the Cci- = Cj). Since, 

 however, the protein ion must equal in concentration the excess chlorine ion the 

 value for the conductivity obtained by subtracting the conductivity of the free 

 HCl from that of the solution may be considered as proportional to the amount 

 of ionized protein. (Recent work, by Noyes, Milner, and others, has rendered 

 questionable the exact interpretation to be put upon conductivity ratios; they 

 very probably do not represent the actual ion concentration in all cases.) The 

 third condition may be experimentally fulfilled by standardizing the apparatus 

 used for the Ch determinations against HCl solutions of known conductivity 

 and taking the Ch as that determined by the conductivity ratios. This method 

 was used in the present experiments. The final values for the conductivity due 

 to the protein-salt ions are the difference between two large figures so that the 

 error is very large and becomes larger as the solution becomes more dilute. 

 Below 1 per cent protein solution (at pH 1.7) the value is meaningless as it 

 usually lies within the limit of error. 



The egg albumin was crystallized three times and then dialyzed under pressure 

 at the isoelectric point until the specific conductivity was lower than 1 X 10"'' 

 reciprocal ohm. The solutions were then brought to a pH of 1.6 to 1.8 with HCl 

 and then diluted with HCl of exactly the same pH. The solutions varied from 

 16 to 1 per cent egg albumin. The time necessary to cause a constant small 

 change in the conductivity of the resulting solution by the same amount of pep- 

 sin was then determined as described previously.^** The reciprocal of this time is 

 plotted in the curves as the rate. The conductivity of the solution was measured 

 on an aliquot p art of the solution to which the equivalent amount of inactivated 

 pepsin had been added. The Ch was determined by the e.m.f. method on this 

 solution. The value given for the specific conductivity of the protein is obtained 

 by sub tracting the specific conductivity of the free HCl from that of the solution. 

 The experimental error of the value is 5 to 10 per cent in the high concentrations 

 and 20 to 30 per cent in the lower. The figures given are the averages of three 

 determinations. All measurements were made at 25° ± 0.01. 



The conductivity and rate of digestion of the egg albumin was 

 measured in this way. It was found in general that the conductivity 

 of the protein solution was, within the rather large limits of error, 

 directly proportional to the rate of digestion of the solution. In 

 other words, the rate of digestion is that predicted by the mass law 

 if the ionized protein is considered as the reacting form. The results 

 of three such experiments are given graphically in Fig. 2 in which 



