802 



Journal of A. gri culture. 



[lo Dec, 1910. 



Assuming a standard arsenate of lead contains approximately 50 per 

 cent, water and 12.5 per cent, arsenic acid, considerable variation will be 

 noted in the brands mentioned above. The water content varies from 

 17.70 per cent, to 67.67 per cent, while the arsenic oxide content ranges, 

 from 10.09 PSJ^ cent, to 24.32 per cent. 



TABI.E II. — Dey Basis. 



Thi.s Table shows the composition of the dry material as eaten by the- 

 insects. The arsenic oxide varies from 34.65 per cent, to 20.80 per cent., 

 the lead oxide from 72.03 per cent, to 61.26 per cent., the water soluble 

 arsenic oxide from 5.06 per cent, to 0.14 per cent., and the water soluble 

 impurities from 11.26 per cent, to 2.36 per cent. The variation in the lat- 

 ter content is evidently due to .some of the salts which are formed as by- 

 products in the process of manufacture not being thoroughly washed out. 

 Considering the comparatively recent introduction of this particular 

 material as a spray an improvement will no doubt be effected in this direc- 

 tion when the result of experience is brought to bear on the preparation 

 and manufacture of the article. 



It will be evident to the grower that some of the arsenates under re- 

 view contain a very high percentage of water, and this may appear un- 

 usual, but the reason advanced is that a better and more uniformly mixed 

 spray can be made from the moist article. If the lead arsenate has been 

 allowed to dry, great difficulty is likely to be experienced in preparing a 

 mixture for use, as the material has, to a certain extent, lost its colloidal 

 property of remaining in suspension. A moisture content of from 40 to 

 50 per cent, has been found to give good results. For the reason given 

 it is advisable that, when a tin or vessel of arsenate of lead is opened and 

 only partly used up, the unused portion be covered with at least an inch 

 of water and that the vessel be covered in a manner which will prevent 

 evaporation as much as possible. 



