1908] 



POND—SOLUTION TENSION AND TOXICITY 



243 



this test. The reagent acidity of lead is correspondingly less than that 

 of copper, although the control figures agree fairly well with those of 

 copper. The point of total inhibition for lead is not determined in 

 this test, so it is not apparent whether the acidity of the reagent and 

 control is identical at that point as was found to be the case with 

 copper and zinc. 



In this test lead proves to be equitoxic with copper and zinc. The 

 figures for copper agree closely wath those preceding. The figures for 

 zinc agree fairly well, the important difference being that at the point 

 of total inhibition the reagent acidity and control acidity are not 

 identical for the w/1024 concentration, although at w/512 the coinci- 

 dence may be noted. The following test is sufficient confirmation of 

 the relation here found. 



TABLE XII 



COPPER 



m 



Control 



Fnzyme 



Increase 



4096 



2048 



1024 



512 



0.13 

 0.20 

 0.40 

 0.70 



0.20 

 0.23 

 0.40 

 0.70 



0.07 



0.03 



O.CX) 



0.00 



LEAD 



0.04 



0.03 

 0.00 



o.co 



ZIN'C 



Enzyme 0.05 per cent. Incubation 5 hours at 40- C. 



All the unboiled zinc solutions were free from sediment. The 

 copper and the lead solutions all contained sediment, though the 

 w/4096 of each contained only the smaUest traces. While* total 

 inhibition may apparently occur in the absence of any precipitation, 



cadmium 



VIII) some inhibition accompanying precipitation. 



