454 Report or INSPECTION WoRK OF THB 
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 
1.68 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 oaide.—The 
amount of copper expressed as the. equivalent of copper oxide 
varies in the 22 samples of Paris green examined from 6.86 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 in 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 
