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 by 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 Pyrethrum 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. cinerarisefolium, 

 the species commonly used in the United States at the present time 

 for the production of insect powder. The three grades of flowers 



