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attenuation of the oil, namely, in giving- the mixture a consistency which 
extends its actions, and in addition, with the soap emulsion, the insecti- 
cide value of the soap. A further objection to the water and oil mixture 
is that wherever the spray collects in drops, as it inevitably will, free 
oil will separate in sufficient amount to injure foliage. An application 
also which depends for its success on the perfect working of a complicated 
apparatus, liable at any moment to get out of order, is hardly a safe one 
to put into the hands of an indifferent laborer. 
Arsenate of lead. — This arsenate, which originated with Mr. F. 0. 
Moulton, of the Gypsy Moth Commission, and is reported to have such 
excellent insecticide qualities, both by the commission and by Mr. 
Fernald, who has experimented with it, is the most promising of the 
new mixtures which have come out during the past year. Our experi- 
ments at Washington show that this mixture has good grounds for the 
claims made for it. Its advantages over the other arsenicals, it will be 
remembered, are its qualities of adhering to the foliage and seeming to 
lack entirely any caustic properties. We have used it on the tender 
foliage of the peach and Osage orange at a strength of 1 pound to 2 
gallons cf water, with glucose enough added to almost make a syrup, 
without the slightest injury to the plants treated. The mixture adhered 
to the foliage through several heavy rains, and gives evidence of lasting 
through the summer. Its insecticide value was tested in experiments 
with the elm leaf-beetle, which, the present season, appeared in great 
numbers in the large elm grove on the Department grounds. The 
experiments were unsatisfactory in one respect, on account of the fre- 
quent occurrence during the spraying season of rains, which interfered 
with the results and rendered a number of repetitions of mixtures 
necessary. 
On May 21 the elm trees were sprayed with the following strengths: 
1 pound of arsenate of lead and 2 quarts of glucose to 120 gallons of 
water, to 75 gallons, and to 50 gallons, applying it in each case to eight 
or ten trees. The check experiment consisted in the application of 
Paris green, 1 pound to 150 gallons water, to neighboring trees. These 
applications all seemed satisfactory, with the exception of the weakest 
mixture of arsenate of lead, which seemed to have had very little effect 
on the larvae. The two stronger applications of the arsenate of lead 
and the Paris green killed at least 95 per cent of the larvae by the 26th 
of May. The rain seeming to have interfered with the action of the 
poison, and it being very desirable to exterminate the larvae, a second 
application was made between the 2Gth and 29th of May. Arsenate of 
lead mixed as above and diluted at the rate of 1 pound of poison to (10 
gallons of water was used, one tree being treated with Paris green at 
the strength employed in the first instance. Light rains immediately 
followed the application, and on the 31st of May the larva' were 
dying, but not rapidly, the Paris green being more prompt in its action. 
The trees were therefore sprayed again on the 4th of June witli a 
