182 EXPERIMENT STATION. [Jan. 



but the gross differences noted in the several samples were evi- 

 dently due to incorrect methods of production. This view was 

 substantiated bv a large number of tests in the station labora- 

 tory, the resulting compounds varying in composition with dif- 

 fering conditions attending their preparation. To be sure, our 

 work was conducted in a small way (2 to 3 ounces at most), 

 but there was no reason to doubt that it would hold equally true 

 on a commercial scale under like circumstances. 



After having failed to obtain satisfactory salts from two dif- 

 ferent companies, and realizing more than ever the lack of man- 

 ufacturing facilities in the laboratory, the matter was brought 

 to the attention of one of the largest American manufacturers of 

 analytical chemicals with whom the problem had previously 

 been discussed. This firm agreed to undertake the preparation 

 of the arsenicals, following general directions furnished by the 

 laboratory. Dry calcium metarsenite and neutral and acid lead 

 arsenates were received from them early in August, and while 

 all were more or less impure the results, on the whole, were 

 encouraging though showing the necessity of further study in 

 order to give more specific directions. Precipitations under 

 varying conditions were continued into January, 1911, at which 

 time the data at hand warranted j^lacing another order with the 

 last-mentioned firm for acid lead arsenate and calcium metarse- 

 nite in form of paste. Explicit directions were furnished by 

 this laboratory as to the method of manufacture. The resulting 

 lead salt proved to be approximately 97 per cent, pure and was 

 accepted. The first lot of lime arsenite was rejected, but the 

 next shipment, over 94 per cent, j^ure, was accepted and em- 

 ployed in spraying tests during the summer of 1911, together 

 with the acid lead arsenate and Paris green. 



The above is a brief statement of some of the difiiculties 

 encountered in securing these three insecticides. In the papers 

 that follow will be found under the headings of Paris green, cal- 

 cium arsenite and load arscMiatos a somewhat detailed descrip- 

 tion of the work performed in this laboratory relative to the 

 several insecticides. Deductions drawn from a small number of 

 samples must be considered indicative rather than conclusive, 

 and their accuracy can be proved only by additional work. 



