1912.] PUBLIC DOCUMENT — No. 31. 201 



Calcium metarsenite was fairlj soluble in cold water, but 

 much more so in boiling water. The ammonium salts, exclusive 

 of nitrite, dissolved about 19 per cent.^ more arsenic than the 

 corresponding sodium salts. The carbonate in both instances 

 proved very effective, followed by the chloride, sulfate and 

 nitrate with only slight differences between the latter. An inter- 

 change of bases must have resulted in many instances to permit 

 the high solubility recorded. Carbonic acid, combined and free, 

 was the most active of any single agent, consequently excess lime 

 should afford one of the best methods of protection under atmos- 

 pheric conditions. Ammonium hydroxide depressed slightly 

 the solubility of the arsenic. 



Calcium metarsenite contains the highest per cent, of arsenic 

 of all the common insecticides, and is quite soluble except in 

 presence of excess lime ; the fineness of its particles and the 

 high power of suspension insure uniform distribution ; the 

 white film readily indicates the surface covered ; and its adhe- 

 siveness provides protection for a reasonable period under aver- 

 age weather conditions. 



C. LexVd Arsenates. 

 Historical. 



F. C. Moulton,- chemist for the Massachusetts Gypsy Moth 

 Commission, was the first to pre])are arsenate of lead for insecti- 

 cidal purposes. He employed lead acetate and sodium arsenate. 

 The work was continued by F. J. Smith, '^ who studied the com- 

 position of the chemicals used, the reactions and other matters 

 pertaining to the manufacture. He stated that ordinary spray 

 material was not a single salt, but a mixture of neutral and acid 

 arsenates, and believed that the relative amount of each de- 

 pended principally upon the source of the soluble lead salt, 

 although temperature and concentration at the moment of pre- 

 cipitation affected the results; in other words, that acetate 'of 

 lead had a tendency, other factors being equal, to yield the neu- 

 tral salt and the nitrate the acid arsenate. 



An electrolytic process for making arsenate of lead was pat- 

 ented by C. D. Vreeland in 1907, using lead, sodium arsenate 



■ Direct comparison. 3 im,^ 45^ pp. 357-371 (1898). 



2 Mass. Bd. Agr. Rept., 41, p. 282 (1894). 



