46 BULLETIN 824, U. S. DEPARTMENT OF AGRICULTURE. 
Kuraz has done more than anyone else in determining the relative 
effectiveness of insect flowers and stems hy the method of testing 
against flies, but there is so much individual variation in the results 
by this method that its value is greatly lessened. 
Of the chemical methods proposed the most valuable is the deter- 
mination of the amount, and more particularly the color, of the ether 
extract. The amount of ether extract in flowers, however, varies 
markedly, as is also the case with stems, 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 is present exclusively in either the stem or 
flower of the Pyre thrum plant. 
AUTHORS' METHOD. 
As has been stated, the addition of ground stems of the Pyrethrum 
plant to the powdered flowers is at the present time the chief form of 
sophistication practiced. Since the amount of added stem can not 
be accurately determined quantitatively by the microscope, although 
it can be approximated, it occurred to the authors that a chemical 
method might be devised for measuring this form of adulteration. 
As long as the active constituent remains unknown, it is necessary 
to rely upon the determination of some essential constituent which 
occurs in the flowers in a reasonably definite amount and which is 
either absent or occurs in other parts of the plant in a widely dif- 
ferent amount. Most of the constituents occurring in the flowers 
that can be accurately and readily determined occur also in all other 
parts of the plant, though in varying quantities. Nitrogen and 
phosphorus occur in the flowers in relatively large proportions, in 
comparison with the amount present in the stems, and upon these 
two constituents the most stress is laid. As indicated by investi- 
gations previously referred to, it may be true that the active insec- 
ticidal principle is soluble in ether and certain other organic solvents. 
Nevertheless, the efficiency of the product can not be measured by 
the amount of this ether extract as now determined, since many of 
the purest samples show a much lower ether extract content than 
some of those seriously adulterated. The color of the ether extract, 
which should be observed before evaporating off the ether, is of more 
value in determining the purity of the powder than the quantity 
of this extract. Its color should be yellow, with never more than a 
slight tinge of green. 
For the purpose of securing data as to the chemical composition 
of Pyrethrum flowers and stems, a number of genuine samples were 
secured. Most of these samples have been the C. ciner arise folium, 
the species commonly used in the United States at the present time 
for the production of insect powder. The three grades of flowers 
