1912.] PUBLIC DOCUMENT — No. 31. 181 



In March, 1910, a persistent effort was made to obtain all 

 help possible in furtherance of the work, as it was then thought 

 that it would be necessary for us to prepare the salts in the sta- 

 tion laboratory. A circular letter was sent to manufacturers 

 of chemicals, particularly those firms making insecticides, ask- 

 ing for information relative to the general process of manu- 

 facture of the several products. A statement was inserted to 

 the effect that the station was not in quest of trade secrets, but 

 merely wished to secure a fairly broad knowledge of the diffi- 

 culties attending the manufacture, and of the impurities likely 

 to be present, so as to be in position to handle the problem intel- 

 ligently. The replies in general contained little or no informa- 

 tion of value. Two large concerns, however, took a more liberal 

 view of the matter and readily furnished any data at their 

 command. One of these companies volunteered to supply any 

 insecticides needed free of cost. Inasmuch as a manufacturer 

 of arsenicals with adequate facilities was unquestionably in a 

 better position to handle the matter, the offer was gratefully 

 accepted. In May large, dry samples of Paris green, copper 

 arsenite, lime arsenite and neutral and acid lead arsenates were 

 received from the factory. A laboratory examination showed 

 that not one of these specially prepared insecticides was entirely 

 satisfactory, the Paris green alone being set aside for actual use 

 in spraying tests. 



The matter now began to assume rather a serious aspect. Was 

 it possible to produce arsenicals of definite molecular ratios or 

 not ? Two companies had signally failed in the attempt, pre- 

 sumably using all the precautions they knew. Letters some- 

 what similar to those sent the manufacturers had also been ad- 

 dressed to several eminent chemists, requesting their opinions 

 as to the preferable precipitants and conditions of manipulation 

 to insure the proper equilibrium for the production of com- 

 pounds of theoretical composition. The substance of their re- 

 plies, while general in character, was to the effect that " the 

 difficulties are inherent in the nature of the compounds," and 

 that arsenites (particularly) are unstable, hydrolizing in the 

 presence of water. The latter fact had long been a matter of 

 record ^ and might excuse slight discrepancies in composition, 



' See p. 185 of this article. 



