1912.] PUBLIC DOCUMENT — No. 31. 195 



Authorities differ as to the arsenite that results from the 

 union of lime and arsenic. Prescott and Johnson ^ state that 

 the arsenites of the alkaline earth are usually ortho compounds, 

 Merck & Co.- and Gooch and Walker ^ give neutral orthoarse- 

 nite of lime, while Comey ■* and Watts' Dictionary ^ recognize 

 the ortho, CasCAsOs)^, the meta, Ca(As02)2, and the pyro, 

 Ca2As205, salts. The latter is designated a mixture of basic 

 salts with 1 molecule of water, 2CaO.As2O3.H2O. So far as 

 noted the formula acknowledged by experiment station workers 

 has been that of the neutral ortho salt, although the siiljject has 

 been given little attention. 



As determined by Colby ^' the suspension, in 1 foot column, 

 of arsenite of lime made according to directions published by 

 Taft was forty-four minutes, and by Kedzie formula fifty- 

 seven minutes. Headden "^ noted that arsenite of lime was 

 almost entireh' soluble in water and in dilute solutions of 

 sodium sulfate and sodium chloride. 



Experimental Results. 

 For the preparation of a high-grade arsenite of lime re- 

 quired for the work in view, precipitation from soluble salts of 

 lime and of arsenic, while more costly, promised a more defi- 

 nite and uniform product. As lime arsenite is noncrystallizable, 

 precipitation from perfect solutions insured better combination 

 and greater freedom from admixtures. The comparative in- 

 solubility of lime, CaO, necessitated the use of a soluble salt. 

 Lime salts of strong oxidizing acids were deemed objectionable 

 on account of possible action on the arsenite and were ex- 

 eluded. The acetate of organic compounds and the chloride of 

 the halogens were selected for trial, but after several tests the 

 chloride was considered preferable. The fused salt was almost 

 invariably employed. It should be free from other bases form- 

 ing insolulde compounds with arsenic. The direct use of 

 arsenous oxide is not advisable with a lime salt, not only for 



• Qual. Chem. Anal., 6th edition, p. 57 (1905). 



'Merck's 1907 Index, p. 113. 



'Outlines of Inorg. Chem. Pt. 2, p. 181 (1905). 



« Diet, of Chem. Sol., p. 41 (1896). 



» Watts' Diet, of Chem., 3d edition, 1, p. 306 (1893). 



f Cal. Exp. Sta., Bui. No. 151, p. 34 (1903). 



' Col. Exp. Sta., Bui. No. 131, p. 22 (1908). 



