fur is the active agent this last method of making would also be the 

 best as nascent sulfur will be produced both by the oxidation of the 

 polysulfids and the breaking down of the thiosulfate. 



Turning to the question whether a long or a short boiling is the 

 better, with these conclusions in mind it is at once evident that boil- 

 ing for so short a time that the sulfur does not all enter into chemi- 

 cal combination produces a wash less effective than it should be. 

 As examination of the sediment at the bottom of the kettle after 

 boiling for half an hour has. frequently shown that this consists to 

 quite a degree of sulfur coated externally with lime, it is clear that in 

 such cases the boiling has not been sufficient, and Haywood finds 

 that it takes longer than this to dissolve all the sulfur. 



The writer appreciates that the foregoing, together with what 

 immediately follows is liable to criticism on the ground that the con- 

 clusions are drawn from too limited experiments, but in view of the 

 fact that we have no more extensive tests in this line to make use of, 

 the conclusions may at least have a tentative value and may be sum- 

 marized as follows : 



1. Take sufficient lime to combine with all the sulfur. 



2. Calcium thiosulfate is the active insecticide and more of this 



is gradually formed by the decomposition of the polysul- 

 fids : therefore, boil to obtain as much of the polysulfids as 

 possible. 



3. Too long boiling produces more thiosulfates and free sulfur at 



the expense of the polysulfids present. The wash will 

 be more active when first applied under these conditions 

 but will not act during as long a time, and it is desirable 

 that it should be active as long as possible. 



4. Letting the wash stand after being made may perhaps give an 



opportunity for the polysulfids and thiosulfate to decom- 

 pose in part, forming substances having no insecticidal 

 value and thus reducing its effectiveness. 



5. From the study of a large number of experiments it seems 



probable that forty minutes to an hour of actual boiling will 

 be needed in order to obtain the greatest amount of the 

 polysulfids. 



