4 MASS. EXPERIMENT STATION BULLETIN 201. 



The statement of total arsenous oxide in the above guaranty may be 

 taken as representing the effectiveness of the material in terms of the 

 killing principle which it contains. The statement of soluble arsenous oxide 

 indicates the maximum amount of injurious compounds of arsenic. 



The above guaranty corresponds to the Federal standard. Paris green 

 as offered for sale in this State fully meets this guaranty. 



To summarize: Paris green is of high arsenic content, and that in the 

 form of arsenous oxide, nominally insoluble in water, but unstable, hy- 

 drolyzing readily, and likely to cause injury unless applied with lime. It 

 is an active poison with a low power of suspension, but admitting of 

 reasonable distribution; a poor indicator without lime of. the leaf surface 

 covered; and of fair adhesiveness and persistence under average weather 

 conditions. 



(b) Arsenates. 



As a group arsenates are rapidly supplanting arsenites, because they 

 have greater stability and are less likely to injure foliage. Of the five 

 arsenates which at one time or another have been used in practice or have 

 been sold in commerce, lead arsenate, developed in 1894 (6), is unquestion- 

 ably the most satisfactory. Calcium arsenate, first manufactured about 

 1912,^ is serviceable, but has a more limited field of usefulness. Magnesium 

 arsenate has been on the market for but two seasons, while the arsenates 

 of zinc and iron are of but minor importance. 



(1) Lead Arsenate. 



F. C. Moulton (7), chemist for the Massachusetts Gypsy Moth Com- 

 mission, was the fu'st to prepare arsenate of lead for insecticide purposes 

 in 1892. The work was continued by F. J. Smith (8), who studied various 

 matters pertaining to the manufacture, and stated that ordinary spray 

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

 Lead arsenate paste appears to have been first prepared commerciall}' 

 about 1895 by the Merrimac Chemical Company of Boston, under the 

 trade name of Swift's arsenate of lead. Disparene, manufactured by the 

 Bowker Insecticide Company of Boston, followed soon after. Dry lead 

 arsenate (Electro) was prepared as an insecticide by the Vreeland Chemical 

 Manufacturing Company of New York about 1909. The California Ex- 

 periment Station mentioned a dry product in 1903, but gave no informa- 

 tion as to its source. Dry, bulky acid lead arsenate was first prepared in 

 1912 by the Corona Chemical Company of Milwaukee, Wis. 



There appear to be three different lead arsenate salts, as follows : — 



1. Acid lead arsenate, PbHAs04. This is the lead arsenate ordinarily sold in New 

 England. 



2. Neutral lead arsenate, Pb3(As04)2. 



3. Basic lead arsenate (9), Pb60H(As04)3. 



1 Correspondence from manufacturers on file. 



