451 Report of iNsr-ECTioN Work of the 



the use of Paris green under the conditions commonly employed. 

 It would, in our judgment, be proper to condemn for use as an 

 insecticide Paris green or other similar materials that yield 

 more than four per ct. of water-soluble arsenic compounds 

 expressed as arsenious oxide when treated for 24 hours with 

 distilled water at the rate of 1000 parts of water for one part 

 of Paris green or arsenic-containing materials. 



The water-soluble arsenious oxide varies in the 22 samples of 

 Paris green examined from 0.51 to 15.69 per ct. and averages 

 1.G8 per ct. Excluding sample No. 50 from the average, the 

 amount of water-soluble arsenious oxide in the remaining 21 

 samples is a trifle over one per ct., very far below limit of harm 

 prescribed for use as an insecticide. Sample No. 50 is to be 

 condemned as wholly unfit for insecticidal purposes on account 

 of the very large excess of arsenic compounds present in water- 

 soluble forms. 



3. Copper in Paris green determined as copper oxide. — The 

 amount of copper expressed as the equivalent of copper oxide 

 varies in the 22 samples of Paris green examined from G.86 to 

 30.73 per ct. and averages 28.97 per ct. However, sample No. 

 50 is clearly shown by its low copper content not to be Paris 

 green at all, or, at least, to contain only a small proportion of 

 Paris green, and we may properly exclude this from our average. 

 Then in the remaining cases the average is 30.02 per ct. of copper 

 oxide, about the same as last year. 



4. Relation of copper oxide to arsenious oxide vn Paris green. — In 

 pure copper aceto-arsenite there are 1.87 pounds of arsenious 

 oxide for one pound of copper oxide. Now, this relation is of 

 value in showing whether Paris green contains more arsenious 

 oxide than it ought. The chief adulterant used in Paris green 

 is arsenious oxide, commercially known as white arsenic. This 

 is used because it is cheaper than Paris green and also because 

 it can be safely added without any danger of reducing the 

 amount of arsenious oxide. In fact, a very poor quality of Paris 

 green can be brought up to the legal requirements by addi- 

 tion of arsenious oxide. However, arsenious oxide cannot be 



