BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 99 
Field trials in search of materials capable of aiding in the removal 
of lead arsenate from the grass on plots of ground to which it is applied 
for controlling Japanese beetle larvae demonstrated that a certain 
proprietary wetting agent when incorporated with the wash water 
normally used produced a decided benefit in this respect. 
TESTS TO DETERMINE THE TOXICITY OF NEW INSECTICIDAL COMPOUNDS TO 
GOLDFISH 
Efforts were continued to ascertain, by means of tests against gold- 
fish, the correlation between toxicity of compounds and the chemical 
groupings they contain, so that the hunt for organic insecticides might 
be more intelligently guided. The work on the monosubstituted 
phenols was greatly advanced by a completion of the comparison of 
the isomeric chlorophenols, bromophenols, and iodophenols. The 
superiority of the iodine compounds over those containing chlorine 
or bromine and the general superiority of the para-substituted com- 
pound in each isomeric group was demonstrated. Work is now under 
way with the hydroxybenzoic acids. 
All such work as this has been heretofore carried out at 27° C, but 
it has gradually become apparent that other temperatures might be 
more suitable for some tests; hence an investigation was begun of the 
temperature-mortality relationship in the case of goldfish exposed to 
the effects of rotenone and phenol, the two standard comparison mate- 
rials now used. The importance of temperature control is readily 
appreciated in view of the fact that the survival time in solutions of 
either of these poisons is only about one-fourth as long at 27° as at 7°. 
ANALYTICAL INVESTIGATIONS 
The routine analytical work of the Division embraced, as usual, the 
analysis of several hundred samples of experimental insecticides being 
tested by other divisions of the Bureau and also nearly 500 samples of 
soil containing lead arsenate from the areas quarantined by the Divi- 
sion of Japanese Beetle Control. 
As usual during the last several years, the collaborative work on the 
determination of minute amounts of arsenic in foods was conducted 
for the Association of Official Agricultural Chemists by the member of 
the Division who acts as referee on that subject. One of the three new 
methods mentioned in last year's report as having been developed by 
him was completely worked out and is under collaborative test this 
year ; it is a titration method as delicate and as speedy as the Gutzeit 
method and decidedly more flexible and accurate. It appears certain 
to displace that time-honored procedure. 
One of the several new procedures for determining residues of 
nicotine on sprayed fruit and foliage, namely, the colorimetric pro- 
cedure using cyanogen bromide and a-naphthylamine, was also devel- 
oped to a very satisfactory state, and, as it can be used in estimating 
the nicotine on a single apple, it is now making possible a detailed study 
of variability of nicotine residues such as was carried out for lead 
arsenate several years ago. 
The colorimetric procedure developed in the Division previously for 
the determination of phenothiazine in spray residues was improved by 
adding a preliminary extraction with petroleum ether, in which the 
