es 
( INSECT POWDER 73 
These results indicated that the material, although very nearly 
ure, was contaminated with other compounds of about the same 
aie point as the toxicsubstance. The yields of redistilled material 
generally represented 0.1 to 0.15 per cent of the powder. 
The preparations were highly toxic to Aphis rumicis, killing the 
insects in dilution up to 1 to 10,000.° 
Great difficulties were encountered in attempting to isolate the 
products of saponification of the material in the case of the alcoholic 
component, which seemed to decompose under all conditions. 
ile this phase of the work was in progress, a series of 10 articles 
on the toxic principles of insect powder was published by Staudinger 
and Ruzicka (S28). Had these articles, describing results obtained 
from 1910 to 1916, appeared before the bureau’s investigations were 
begun, all this work on the constitution of the active principles 
of Pyrethrum would have been unnecessary: These investigators 
had isolated the toxic principles and had practically solved the 
problem of their chemical nature. 
Staudinger and Ruzicka used the following method: The powdered 
flowers were extracted with light petroleum ether. The extract was 
evaporated and the residue was extracted repeatedly with methyl 
alcohol, which removed the toxic substances, together with fatty acids 
and other impurities. By strongly chilling the alcoholic solution, a 
large part of the impurities was removed. The methyl alcohol was 
expelled and the residue taken up with petroleum ether. Fatty acids 
were extracted from the solution by shaking with potassium carbonate 
solution and transforming the potassium soaps into calcium soaps by 
_ addition of calcium chlorid. This treatment was necessary in order 
to avoid the formation of emulsions. The petroleum ether solution 
was evaporated and the residue extracted with methyl! alcohol, which 
solvent was in turn removed and the resulting product again dissolved 
in petroleum ether and the solution once more treated with potassium 
carbonate solution. Upon evaporation of the solvent, a crude 
product was obtained in quantity corresponding to 0.47 per cent of 
the powder. This consisted of about 50 per cent of the active sub- 
stances. By distillation of this crude product in a high vacuum, a 
highly active oil was obtained. It was not possible, even by repeated 
distillation, to completely purify the material, however. ‘Treating 
the distilled material with semicarbazid in methyl! alcohol gave a semi- 
carbazone, which could be recrystallized and thus prepared in nearly 
pure condition. By hydrolysis with oxalic acid, a practically pure 
compound was prepared. This compound, represented by the formula 
C,, H,,O;, was named pyrethrin I. It is an ester of a ketone-alcohol 
and is highly toxic to insects. Thesemicarbazone can be hydrolyzed 
with methyl alcoholic-sodium hydroxid into the semicarbazone of the 
ketone-alcohol and an acid. 
The acid which Staudinger and Ruzicka named chrysanthemum 
acid is the same as the pyrethronic acid of Yamamoto, and its con- 
stitution was determined by oxidation to transcaronic acid and ace- 
tone by means of ozone. It is represented by the structural formula 
(CH;)) C-CHCH=C(CH3)2 
NT 
_ 
COOH 
9 Toxicity tests were conducted by C. H. Richardson, Bureau of Entomology. 
