oD8 RErOKT OF iNSrECTIOX WOUK OF THE 



DISCUSSION OF RESULTS OF CHEMICAL ANALYSIS. 



1. 7'otal arsenions oxide. — In the 40 samples of materials sold 

 as Paris green, examined by us, the amount or arsenic equiva- 

 lent to arsenious oxide, varies from 56.13 to 62.87 per ct., and 

 averaged 58.10 per ct. This average is over one per ct. higher 

 than that found last year, and is about one-half per ct. below 

 the equivalent of arsenious oxide contained in pure copper aceto- 

 arsenite. So far as the total arsenic content is concerned, the 

 amount found indicates a high quality of Paris green. The 

 variation is about the same as last year and, excepting four 

 samples, is v^ithin surprisingly narrow limits. Where the total 

 amount of arsenic present in Paris green the only point to be 

 considered, the quality would be regarded as very satisfactory, 

 but we must consider at the same time the amount of water- 

 soluble compounds of arsenic present in Paris green. 



2. Water-soluhle compounds of arsenw. — The presence of water- 

 soluble arsenic in Paris green is seriously objectionable owing 

 to the fact that soluble arsenic compounds injure foliage. 

 Hilgard, of California, states that in the dry climate of Cali- 

 fornia, Paris green injures foliage when it contains an equiva- 

 lent of more than four per ct. of arsenious oxide in the form 

 of soluble arsenic compounds. The water-soluble arsenic most 

 commonly occurring in Paris green is in the form of arsenious 

 oxide, commercally known as common white arsenic. 



The method of analysis used by us in determining the amount 

 of water-soluble arsenic compounds in Paris green should show 

 the full amount of such compounds that would be found in 

 actual field work where Paris green is mixed with water at the 

 rate of one part by weight of Paris green to 1000 parts of water 

 and the mixture used soon after preparation. By longer extrac- 

 tion with water, larger quantities of soluble arsenic compounds 

 can be obtained; but for our purpose, it is desirable to approxi- 

 mate the amount likely to be found in actual field practice 

 in the use of Paris green under the conditions commonly em- 

 ployed. It would, in our judgment, be proper to condemn for 



