INSECTICIDES AND FUNGICIDES: CHEMICAL COMPOSITION AND 
EFFECTIVENESS. 

PARIS GREEN. 
Among the most important insecticides now on the market is Paris 
green, and this article deserves first consideration. Paris green, if 
perfectly pure chemically, is a compound made up of three substances— 
arsenious acid, acetic acid, and oxide of copper—joined to each other 
in a chemical combination called copper aceto-arsenite. These should 
be present in the following proportions: 
Per cent. 
Mnemronctacitte. 4.22. eateries ne basa sce <i eens cca 58. 65 
@appemoside $40 S 7 i ohaps Ses <p eaSeere s eis 3129 
Dart eee Pete ae alo eae cio ata Stele esi stasis own aaa n= eae 10. 06 
Use of arsenious acid in free state——Because of faulty methods of 
manufacture, however, and also because arsenious acid is cheaper than 
the other constituents of Paris green, large amounts of this substance 
are sometimes present in the Paris green on the market not combined 
as it should be with the other two constituents, but present in the free 
state. A sample of this kind will cause great damage to the foliage 
by scorching, and the avoidance of such Paris green can not be too 
strongly recommended. The maximum amount of free arsenious acid 
that should be allowed in Paris green has been found in Califprnia to 
be 4 per cent and in Idaho between 4 and 5 per cent. 
There is no easy test by which one who is not a chemist can recog- 
nize the presence of free arsenious acid in Paris green. Intending 
purchasers should consult bulletins on the subject which give the names 
of the various manufacturers, along with an analysis showing how much 
of the arsenious acid is free and how much combined, as it should be 
with the other constituents. 
Addition of calcium sulphate.—Another method of adulterating Paris 
green is by the addition of calcium sulphate (gypsum). It is hardly 
necessary to state that this substance is absolutely worthless as an 
insecticide and is only added to give weight. Such an adulteration 
as this is more rare than that first mentioned, and is also much easier 
of detection. To apply the test for this form of adulteration take 
= 
‘ 
