32 -VNM AL KKroK'is ( u' I n:i'A iiJM 1 INT (»F A< iKicri/mn:. VXM 
<lrnt;illy. certain features of the (nit/eit luetluHl for arsenic- were improved, 
and rhey njay be useful in further inii)rovin;; the antimony method just 
mentioned. 
CHEMK AL INVKSTIGATIUNS TO DKVKLOP INORGANIC INSECTICIDES 
Last year's report deserihed tlie work on eomniereial caicium arsenate which 
showed how complex this important insect icid<' is, and how that complexity 
is the result of faihin^ to reach e(iiiilil)rium in the manufacturing jtrocess. This 
year attention was devoted to the development of a method of preparing cal- 
cium arsenate so that e(inilibriinn will result in every case, and the composition 
itt the resulting product therefore he predictable from the proportions of lime 
and arsenic acid used. It was found that by atomizing the acid into the lime 
slurry while the latter was violently agitated, the local excesses resi)onsible 
lor disturbed equilibria were i)revented, and the finished i>roduct turned out 
every time to be what the phase-rule studies had indicated it should be. It 
is thought that this method can be adapted to connnercial manufacture. 
A survey of about 40 of the many brands of dusting and wet table sulphurs 
on the insecticide market was undertaken and the determination of their physi- 
cal pr(»perties almost completed. Complete particle-size analysis was made* on 
all of them, and, as in the case of the calcium arsenates and paris green al- 
ready reported on, great differences were foiuid among the various brands. 
This work is part of the general program of studying the relation between 
particle size and insecticidal efficacy of dusting and spraying materials. A 
so-called air classiher was obtained and set up, and with this machine con- 
siderable quantities of paris green of definitely different particle sizes have 
been prepared and offered to cooperating entomologists for toxicity tests. 
Much work was done on lead arsenate in relation to its use as a soil insecti- 
cide for .Japanese beetle grubs. A new and shorter method of sampling treated 
nursery plots was worked out. and nearly 1,(100 samples were analyzed prepara- 
tory to retreatment. The uniformity of dei)osits obtained on grass ])lots was 
determined, and a start made on the development of a method of chemical 
analysis for judging the toxicity of a treated soil rather than merely its 
arsenic content. The effect of various materials in counteractinir the deleteri- 
ous action of lead arsenate in soil on plant < growing therein was studied., 
and promising results were obtained with certain iron compounds, such as bog 
iron ore and a commercially available chemical by]u-oduct. ferric hydroxide. 
Some work was done on the homologs of jiaris green, and the possibility 
demonstrated of preparing such greens directly from vegetable, animal, and fish 
oils instead of from the acids they contain. 
CHEMICAL INVESTIGATIONS ON FUMIGANTS FOR CONTROL OF INSI.CT PESTS 
Much of the work done at Whittier. Calif., on (he fiunigation of the California 
red scale on citrus was devoted to the betterment of experimental procedure, 
and various distinct improvements were worked out. First, the concentration 
of liydrocyanic acid and the length of expitsure necessary to give practically 
KK)-perc(Mit kill was determined to be 2.1 milligrams of hydrocyanic acid per liter 
for 40 minutes. Then a procedure was worked out for preconditioning and post- 
conditioning the experimental fruit under certain definite conditions of 
temperature and liumidity so that the scales can be expected to be in a much 
more uniform stale of activity when fiunigated. As a result of this, experi- 
mental figures can be duplicated now much better than ever before. 
In connection with the work on the fumigation of slortMl cereal products 
which is luider way at tlie Manhattan. Kans.. laboratory, advances were made 
in the techiiupie of fumigation in vacuum vaults. In addition, studies were 
made rtf the retention of hydrocyanic acid by flour and by rice, and of the 
flissipation of the hydrocyanic acid with the lapse of lime and U])on boiling. 
I'inally. the (effect of \arious fumigants ui)on ])opcorn. as evidenced by tlie bulk 
of |>opjM'd c(»rn i>ro(luce<l. was studied, liydrocyanic acid apiK\irs to have no 
effect. cMi-lxui disulphide lowers the bulk at (he higher concentrations, and 
ethylene dichloride has a pronounced efTect wliicli lessens with the time of 
keeping (he fumigated corn before ])oi)ping. 
A study of the fiunigation of veg(»(:ibl<\s with methyl bromide was undertaken. 
So far. attention has been (hnoted to (he d(^ve]opmen( of methods of analysis. 
\\itli special reference li> one \eg(>t;ible. string Ix^ins. 
