38 BULLETIN 824, U. S. DEPARTMENT OF AGRICULTURE 
Windisch (S30), in 1921, reported the results of analyses of five 
samples of commercial insect powder sold as “‘Zacherlin.” The total. . 
ash content varied from 6.84 to 9.78 per cent, and the sand content 
(ash insoluble in hydrochloric acid) from 0.27 to 0.88 per cent. Costa 
(S7, S8) has described a method of determining the aqueous extract of 
insect powder. Calculated on a dry basis, the aqueous extract of 
closed insect flowers varies from 22 to 25 per cent; that of open flowers 
from 12 to 14 per cent; and that of stems from 9 to 11 per cent. 
SUMMARY OF METHODS 
Satisfactory chemical and microscopical methods have been 
developed for detecting the addition of other species of flowers, 
curcuma, and Pyrethrum stems to genuine insect powder. These 
methods, however, do not show accurately the extent of this adultera- 
tion, although the quantity of stems can be approximated by com- 
paring under the microscope the unknown mixture with known mix- 
tures of powdered flowers and stems. Of course, the quantity of an 
inorganic adulterant lke lead chromate may be accurately determined 
by chemical analysis, but such adulteration is now rare. Probably 
more than 90 per cent of the adulteration of insect powder at the 
present time is with ground Pyrethrum stems. 
A promising microscopic method for examining insect powder is 
that proposed by Trottner, in which the number of pollen grains in 
the weighed quantity of sample is estimated. This number, however, 
varies so much in different powders of equal effectiveness that a 
rigorous quantitative application of the method is impossible. 
Kuraz Mae done more than anyone else to determine the relative 
effectiveness of insect flowers and stems. The individual variations 
in his results, however, lessen the value of his method of testing 
against flies. 
Of the chemical methods proposed the most valuable is the deter- 
mination of the quantity, and more particularly the color, of the ether 
extract. The quantity of ether extract in flowers and stems, how- 
ever, varies markedly. and its determination alone is not sufficient to 
enable the analyst to establish standards. 
No element or compound that can be detected with the present 
methods of analysis occurs exclusively in either the stem or flower 
of the Pyrethrum plant. 
WRITERS’ METHOD 
The addition of ground stems of the Pyrethrum plant to the pow- 
dered flowers is now the chief form of sophistication. As the quantity 
of added stem can not be accurately determined by the microscope, 
although it can be approximated, a chemical method for measuring 
this form of adulteration has been devised. 
The insecticidal ingredients of Pyrethrum flowers are known, but 
no method for an accurate quantitative determination of them has 
been devised. It is therefore necessary to rely upon the determina- 
tion of some essential constituent present in the flowers in a reasonably 
definite quantity and either absent from other parts of the plant or 
present in a very different quantity. Most of the constituents of the 
flowers that can be accurately and readily determined occur also in 
all other parts of the plant, although in varying quantities. The 
proportions of nitrogen and phosphorus in the flowers are large as 
