5 o6 
Journal of Agricultural Research 
Vol. XXIV. No. 6 
conditions. Haywood and McDonnell {12) point out the great variation 
in the composition of the diflferent samples analyzed, and this, no doubt, 
has had very much influence on contradictory results. Lead arsenates 
which are safe to use under dry arid conditions may cause serious injury 
under conditions of high humidity. Atmospheric conditions following 
sprayings have a great influence on the action of the spray mixture of 
the foliage, and for this reason duplicate experiments, when a short 
time intervenes between them, may not control. Gillette (ri). Wood- 
worth and Colby (57), and others concluded that leaves kept perfectly 
dry can hardly be injured by the arsenites, but that under conditions of 
high humidity the injurious action is greatly increased. However, at 
the present time lead arsenate is recognized as the standard insecticide, 
not only for orchard spraying but for field and truck crops as well. 
Against insects it is known as a rather slow poison, but it is effective. 
In this respect there is considerable difference in the two forms, viz, the 
triplumbic and the diplumbic ortho-lead arsenate, due in all probabilities 
to the difference in their arsenic content, which is the poisonous principle. 
LONDON PURPLE 
PREPARATION 
London purple consists of calcium arsenite, calcium arsenate, and inert 
ingredients as dye residue, dirt, etc., and is prepared by boiling a purple 
residue from the dye industry with slaked lime. The analysis on a 
package recently received at this station was as follows: Total arsenic 
(As), 21 per cent; active ingredients, calcium arsenate and calcium 
arsenite, 54 per cent; inert ingredients, dyestuffs, etc., 46 per cent; 
arsenic (As) in water soluble forms, per cent. Analysis by our 
station chemist substantiated the claim as to the total arsenic content. 
If judged from the arsenic content, London purple has only about one- 
half the killing strength of Paris green when used as an insecticide. 
• USE AS AN INSECnaoE 
The name “ London purple” was suggested by Dr. C. E. Bessey (private 
correspondence) in 1878, and he was file first to use it as a substitute for 
Paris green for the destruction of the potato beetle. Doctor Bessey was 
one of the three men who first received sample packets of London purple 
sent by a London firm ^ in a letter dated September 7, 1877. 
On October 2, after an exchange of letters, the firm forwarded to him 
three kegs of the material, which was the first shipment sent to America. 
The results of the experimental work of Bessey and Budd were favorable 
to the new poison, and it was soon recommended as a substitute for Paris 
green, not only for the destruction of the potato beetle but for other 
insects as well. 
The value of this material was recognized with surprising rapidity, 
probably due to its cheapness and the ease with which it could be applied. 
The principal objection to its use was its injurious action on the foliage 
of plants. Its burning tendencies were undoubtedly due to the soluble 
arsenic it contained, and it was not uniform in composition. The early 
analysis of London purple shows variations in amounts of arseniou^i 
oxid of from 31 per cent to nearly 60 per cent. However, at the present 
time the manufactiurers claim to have perfected a process by which the 
composition of London purple is as uniform as that of Paris green or 
others of the standard insecticides. 
3 Hemingway & Co. 
