117 
as much as the Paris green mixtures. This explains why white arsenic 
if applied freshly mixed will injure foliage least, and after long stand- 
ing in water most, of these three arsenites. A large number of appli- 
cations of London purple, Paris green, and white arsenic in water to 
foliage, made by the writer at the Colorado Experiment Station during 
the summer of 1891 add increased evidence of the correctness of the 
above conclusions. White arsenic in the proportion of 1 pound to 16 
gallons freshly mixed and applied to Osage Orange, Black Thorn, Ap- 
ple, and Plum burned 7 per cent (estimated) of the foliage of Osage 
Orange as its greatest injury. One pound to 64 and one pound to 128 
gallons produced very slight spotting of Plum leaves only. 
During the present summer the writer has freely dusted pure pow- 
dered white arsenic upon the foliage of Box-elder, Elm, Plum, and Grape 
without producing any injury to the leaves. 
PARIS GREEN. 
This poison is an arsenite of copper and gives, on analysis,* about 
68 per cent of arsenious acid (analyses differ considerably in the amount 
of arsenic obtained). It is said to be insoluble in water, but chemical 
t tests made at the North Carolina and New Jersey Experiment Stations 
show from 0.04 to 0.08 per cent of quickly soluble arsenic. The small 
amount of soluble arsenic in Paris green accounts for its being less 
harmful to plants than London purple as ordinarily applied. It should 
be remembered, however, that some have found Paris green more inju- 
rious to foliage than London purple, and that Prof. L. H. Bailey, aided 
by the assistant station chemist, reported in Bulletin xviii of the 
Cornell Experiment Station that peach leaves burned by Paris green 
had no arsenic in their tissues and concluded that the injury was due 
wholly to external contact. Plants £ sprayed with dissolved arsenic at 
the Iowa Experiment Station in 1888 had arsenic in the tissue of the 
leaves after 48 hours. So it is possible that the injuries produced by 
Paris green upon plants, and its reputed quicker § and more certain ac- 
tion upon insects may be due to some property it possesses different in 
degree or kind from properties possessed by London purple or white 
arsenic. 
It has also been stated by Mr. Woodworth (in Bulletin 14, p. 14, of the 
Arkansas Experiment Station) that Paris green is slower in its effects 
upon foliage than is either London purple or white arsenic. It is pos- 
sible that some who have reported upon the injuries to foliage have not 
waited long enough to see the full effect. Not less than three weeks 
should elapse from time of application before final notes are taken. 
* Bull. 18, Cornell Univ. Agr. Exp. Sta., p. 37; Ann. Rep. N. J. Exp. Sta,, 1890, p. 
526. 
t Bull, lib, N. C. Agr. Exp. Sta., p. 6; Anu. Rep. N. J. Exp. Sta., 1890. 
t Bull. 2, Iowa Exp. Sta., p. 33. 
§ Bull. 17, Ala. Exp. Sta., p. 6; Ann. Rep. St. Ent. of 111., 1885 (experiments with 
Codling Moth) ; Bull. 12, Del. Exp. Sta. ; Bull. 48, Cornell Exp. Sta,, p. 272. 
