130 



wliicli three horizontal portions A, B, and Care to be distinguished. 



A indicates the motionless phase of the galvanometer during the 

 time when there is only the oxalale-plasm between light-source and 

 thermo-battery; a. indicates the moment when CaCl, is added; the 

 first moment the plasm becomes clearer, see b., which is owing to 

 the dilution of the plasm. But directly after this the liquid becomes 

 very turbid which is due to the forming calciumoxalate ; the curve 

 ascends almost vertically, see c, and would gradually liave reached 

 the i?-level, if not an irregular weakening of the light had been 

 brought about by the stirring rod; the jerks in the curve at d. 

 illustrate this irregularity, so that thej' have nothing to do with the 

 process of turbidity. The calcium oxalate is not |>recipitated but 

 remains in suspension; for a few uiinutes the galvanometer remains 

 constant, as shown in the Z^-portion. 



Up to this moment coagulation is out of the question. Soli- 

 ditication commences at e. at a certain moment, apparently quite 

 independently from the inital turbidity (formation of calcium-oxalate), 

 and simultaneously the second phase of turbidity begins. It is this 

 portion of the curve that interests us most. Its shape is an objective 

 illustration of the coagulation process. 



It appears that this coagulation starts very slowly, then proceeds 

 more quickly until a maximum rate is attained, after which a 

 retardation sets in again until the terminal value is ultimately 

 reached. 



I will not discuss here the nature of this curve, but only point 

 to the method, which enabled me to typify any given portion of 

 the curve by a tigure. I note the exact time at which certain levels, 

 e.g. 74 ^"d V4 of the difference of the B-, and C-level are reached ; 

 the time-difference is my control-number. 



My researches were performed in the Physical Laboratory of the 

 Utrecht State-University, where I had the freedom of the instruments. 



Utrecht, December 1921. 



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