ENTOMOLOGY AND PLANT QUAUANTINE 
81 
Certain other iiisectieidal plants and their active constituents were studied. 
The active material in quassia wood was found to contain two isomeric ma- 
terials called quassin and neoquassin, and much information was obtained 
toward determining their structures. Another isomeric material, picrasmin, 
was obtained from picrasma wood, and its close relationship to quassin dem- 
onstrated. The study of IlaijloijJiyton ciniicidina was concluded, without any 
very definite results. An active principle designated helenalin was ol)tained 
from Helenium autumnalc and another one called tenulin from H. Jcnuifoliuin, 
and both materials were studied as to structure. 
CHEMICAL INVESTIGATIONS TO DEVELOP SNYTHETIC ORGANIC INSECTICIDES 
Over 100 organic compounds were synthesized and sent out for insecticidal 
testing, mainly against codling moth larvae, mosquito larvae, cabbage-infest- 
ing caterpillars, the tobacco hornworm, and the Japanese beetle. Several 
showed sufficient activity to warrant the filing of patent applications covering 
them and the classes to which they belong. One patent covering aryl thioxins 
( phenothioxin) was obtained. 
The attempt to better adapt plienothiazine to field work was continued. 
Its high toxicity to codling moth larvae is admitted, but its application is 
rendered difficult by its poor wettability, and the deposits do not adhere very 
well. Laboratory tests have shown that a heavier deposit of phenothiazine is 
obtained when it is mixed with calcium chloride and soap, which produce a 
sticky calcium soap capable of holding the phenothiazine. The conditions of 
exposure which lead to the decomposition of phenothiazine were studied. 
CHEMICAL INVESTIGATIONS ON THE REMOVAL OF SPRAY RESIDUE 
The removal of lead arsenate from apples was again studied in detail at 
the Washington, D. C, laboratory. Fruit of several varieties, and sprayed in 
several ways, was washed with various solutions at several temperatures and 
in three kinds of machines. A total of 502 samples were analyzed. Residues 
were lighter in general than in the previous year, and were more easily re- 
moved. A varietal effect on ease of removal was evident, and delay after 
picking caused trouble. The effect of mineral oil in building up of deposit, 
and in the hindering of washing, was again demonstrated, as was the superi- 
ority of the brush-flood machine. A study of 48 of the samples failed to 
show any significant change in the ratio of lead to arsenic, previously claimed 
by other investigators. At the Yakima laboratory 132 samples of apples 
coming from spray plots that had received cryolite were analyzed for fluorine 
residues, and by the use of the analytical methods developed by the Food and 
Drug Administration it was demonstrated for the first time in our work that 
these residues can be satisfactorily removed by efficient washing equipment. 
At the Vincennes, Ind., laboratory it was demonstrated that lead arsenate resi- 
dues from first-brood cover sprays are more difficult to remove than those 
from the second-brood sprays, regardless of the quantity of residue present 
at harvest, and that the use of adhesives with or following lead arsenate 
sprays complicates residue removal. 
The results of the study of the lead content of chewing tobacco and snuft', 
presumably residues from the insecticidal dusting of tobacco, were published. 
A method of estimating phenothiazine spray residues was developed. It 
was shov^^i at Yakima that the spray procedures giving good control of codling 
moth larvae were those that deposited over 20 micrograms of phenothiazine 
per square centimeter of apple surface, and that such residues can be easily 
removed by washing. Also, it was shown that phenothiazine residues decom- 
pose somewhat from exposure to heat and light, a change that seems to be 
accelerated by oils, waxes, and finely divided materials such as bentonite. 
A method of determining boron in rice dusted with borax v>-as worked out. 
and the treated rice was shown to contain from to 200 parts of boric acid 
per million. It was demonstrated that the removal of the hull in the polishing 
process also removed the greater part of the residue. 
A microchemical method for determining antimony was developed to the 
point where it is suitable for the study of the spray residues resulting from 
the use of tartar emetic against fruitflies. It resembles the Gutzeit metliod 
for arsenic, and determines from 25 to 150 micrograms of antimony. Inci- 
2469.5— .37 6 
