54 



BULLETIlSr 824^ U. S. DEPARTMENT OF AGRICULTURE. 



Table 32. — Nitrogen in stems picked from "closed" floxvers (Chrysanthemum, cinera- 



rixfolium). 



Sample No. 



Nitrogen, 



N. 



Sample No. 



Nitrogen, 



N. 



14921 



Per cent. 

 1.60 

 1.40 

 1.52 

 1.54 

 1.64 

 1.77 

 1.21 

 1.54 



17749 



Per cent. 

 1.52 



14934 



■ 17750 



1.52 



15009 



17821 



1.57 



15136 



18008 



1.63 



17389 







17394 



1.21 



17395 



Maximum 



1.77 



17621 





1.53 









It was found that a determination of the nitrogen and of the phos- 

 phorus, together with a quahtative ether-extract test (to determine 

 its color), were sufficient to determine the presence and approximate 

 percentage of stems, 



• In but few of the pubUshed analyses of insect powder, where ether 

 extract is given as one of the determinations, is the kind of ether 

 specified. In some methods the powder is simply shaken up with 

 ether, filtered, and an aliquot evaporated. Dietze (70) has shown 

 that the results do not agree when ether of specific gravity 0.720 

 and of 0.735 is used. Ordinary ether contains some alcohol and 

 water and extracts from insect-powder material other than the active 

 insecticidal constituents. For concordant results, the ether used in 

 making the extractions must always be of the same grade. Anhy- 

 drous, alcohol-free ether would seem to be the best solvent to use, 



Pyrethrimi flowers usually yield an intensely yellow ether extract, 

 whereas the stems give one of a strong green color. The odor of the 

 extract from the flowers is also characteristic. In the examination of 

 commercial insect powder the presence of a material amount of 

 powdered stems can always be detected by the green color of the 

 ether extract. Its quantitative estimation is, however, of little value 

 in determining the amount of stems present, and this determination 

 was made in only a few cases, the method employed being as follows : 

 The 2 grams used in the determination of moisture were transferred 

 to an extraction thimble and extracted in a suitable apparatus for 

 16 hours with ether that had been freshly distilled over metallic 

 sodium. After extraction, the ethereal solution was evaporated to 

 dryness on the steam bath and dried to constant weight at the temper- 

 ature of boiling water. 



The petroleum-ether extract was determined in a few cases by 

 thoroughly extracting 2 grams of the powder in a Soxhlet apparatus 

 with commercial petroleum ether (specific gravity, 0.640; boiling 

 point, 30° to 65° C), evaporating the extract on the steam bath, and 

 drying for a few minutes in an oven at 100° C. 



