ASPECTS OF ADSORPTION PHENOMENA 185 



the conductivity commenced to go up again, finally becoming 160 

 gemmhos. If, therefore, we take this last as the true value, the 

 amount of electrolyte taken up by gelatin was very small, a difference 

 of 3 gemmhos only between the two cases. If, on the other hand, 

 we take the lowest value to which the conductivity fell, the difference 

 is considerable, viz., 75 gemmhos. 



In the case of the commercial gelatin and its equivalent calcium 

 sulphate solution, the rise produced by the addition of 1 5 c.c. of 

 saturated calcium sulphate and phosphate was 68 gemmhos in the 

 watery solution and 56 gemmhos in that where the gelatin was 

 present, a difference of 12 gemmhos. The addition of the electrolyte 

 at first caused a rise of 106 gemmhos where the gelatin was present, 

 it fell to 72 in one hour, but the final value was not reached for 

 several hours, as opposed to the first case, where it was reached in 

 two-and-a-half hours. 



This experiment affords a certain amount of evidence that 

 electrolytes are taken up by gelatin, but does not distinguish between 

 adsorption and chemical combination. As we shall see later, the effect 

 of heat shows it to be, in all probability, a case of the former. 



III. THE KINETICS OF ADSORPTION 



i . Velocity of Reaction. 



Very little information is to be obtained as to the rate at which 

 bodies are taken up by adsorbing substances. A few experiments that 

 I have made on this question may therefore be of interest. 



Experiment : 50 c.c. of 20 per cent, alcohol in test-tube lined with 

 filter-paper. In thermostat at 39. When warmed, i c.c. warmed 0*5 

 per cent, congo-red added, stirred, conductivity taken at intervals by 

 pipette electrodes. The curve (Fig. 3) shows the time course of the 

 diminution of conductivity. It will be noted that the curve is hyper- 

 bolic and that it arrives nearly at the asymptote in 10 minutes. At 

 this temperature the velocity is considerable. The first part of the 

 curve in all probability escaped observation, owing to the great initial 

 velocity of the reaction as shown by the shape of the curve. 



