Ball — On the Action of Pectase. 353 



Experiment II. 



The viscosimeter was kept in a tank of water at 14° 0. The usual 

 quantities of Syringa sap and pectin solution, which had been kept in 

 separate test-tubes immersed in the tank for half-au-hour, were mixed, and 

 tlie mixture introduced into the viscosimeter. Viscosity determinations were 

 made every five minutes, and tlie results are plotted on a curve. The viscosity 

 increases rapidly until a maximum is reached, and then decreases rapidly. 

 Towards the end of the experiment the homogeneous gel which had previously 

 been formed became broken up into clumps of more solid matter suspended 

 in a liquid. These clumps gradually settled down to the bottom of the 

 viscosimeter, so that further determinations of viscosity were useless, as the 

 capillary tended to become clogged, and irregular readings resulted. 



Experiments III and IV. 



An experiment which had previously been conducted showed that sap, 

 extracted from the leaves of Syringa and saturated with toluene, had 

 practically lost its activity in coagulating pectin after about a fortnight. 



In the following two experiments sufficient sap was extracted for use on 

 two consecutive days. 



In tlie first experiment the method adopted was exactly similar to that of 

 Experiment II, but the temperature was kept constant at 21° 0. The results 

 obtained are plotted on a curve which shows that a maximum viscosity was 

 reached, but the time taken to reach the maximum was longer than in the 

 previous experiment. The cause of the delay will be discussed later. 



In all the experiments up to the present the pectase was acting in a slightly 

 acid medium, due both to the acidity of the cell sap and to tiie fact that the 

 pectin solution itself was faintly acid. 



In Experiment IV the sap was neutralized by the addition of a few 

 drops of sodium hydrate solution. 



The sap was accidentally made slightly alkaline to litmus, and more acid 

 had to be added to make it neutral. This resulted in a slight increase in the 

 total quantity of electrolytes present, and also in the substitution of sodium 

 lor hydrogen ions. The pectin solution was also neutralized, and the 

 experiment conducted similarly to the last. 



The curve obtained from the results is interesting. It will be seen that 

 the rate of increase in viscosity is not very different from the rate of increase 

 in the last experiment, but a maximum is attained at a much lower viscosity. 

 The reason for the decrease in viscosity after the maximum is reached may be 



