38 



BULLETIN 824, U. S. DEPARTMEl^T OF AGRICULTURE. 



as a filter. Moisten with ether (0.735 sp. gr.) ; close the top of the syringe and macerate 

 for 30 minutes; percolation may then proceed, the powder being repercolated with 

 the same fluid fom* times, and finally washed through with sufficient ether to make 

 up 1 fluid ounce. The resulting percolate should be of a rich yellow color; if a pro- 

 nounced green color be the result the sample may be discarded at once. 



This percolate should be evaporated at 200° F., and should weigh not less than 

 3.75 grains (=3.75 per cent), and should have the characteristic odor of the flowers 

 * * *. Insect powder ground from selected closed flowers is sensibly free from 

 chlorophyll, whereas traces of it (less than 0.5 per cent) will be found in powders 

 prepared from mixed and half-open flowers, and in the foreign groimd insect powders 

 it often amounts to from 50 to 80 per cent of the total ether extract. 



Durrant suggests the determination of the amount of chlorophyll 

 when it is present in large amount, by converting it to glucose and 

 determining that in the regular way. He concludes: "The value of 

 insect powder is in direct proportion to the combined amount of 

 essential oil and soft acid resin and in inverse proportion to the 

 amount of chlorophyll — both statements to be read together." 



Francis (84) determined the ether extract of a powder made from 

 "ground flowers only," one from "ground stems only," and of a 

 "mixture of these two in equal proportion," to be as follows: Ether 

 extract of flowers, 6.07 per cent; ether extract of mixture, 3.82 per 

 cent; ether extract of stems, 2.25 per cent. He states, "The ether 

 extracts in each instance had a decided green color, indicating the 

 presence of chlorophyll." 



Dowzard (71) estimates ether-soluble matter as follows: "Two 

 grams of the sample are mixed with 50 cc. of ether in a stoppered 

 cylinder, the mixture being shaken at intervals during 2 hours; 25 

 cc. (=1 gram powder) of the clear ethereal solution is evaporated 

 in a tared beaker and the residue weighed." He also makes use of 

 physiological tests: "Two grams of the sample is transferred to a 

 beaker, a cockroach is then introduced and the number of minutes 

 which elapse before the insect becomes stupefied are noted." He 

 gives the results of the examination of 12 samples shown in Table 14. 



Table 14. — Examination of insect powder (Doivzard). 



Sample No. 



Period of 

 physio- 

 logical 

 test. 



Ether 

 extract. 



Sample No. 



Period of 

 physio- 

 logical 

 test. 



Ether 

 extract. 



Sample No. 



Period of 



physio 



logical 



test. 



Ether 

 extract. 



1 



Minutes. 

 4 

 5 

 5 

 5 



Per cent. 

 8.4 

 7.6 

 7.4 

 6.6 



5 



Minutes. 

 6 

 5 

 5 

 5 



Per cent. 

 6.4 

 5.6 

 5.4 

 5.0 



9 



Minutes. 

 7 

 8 

 12 

 12 



Per cent. 

 5.0 



2 



6 



10 



3.2 



3 



7 



11 



4.2 



4 



8 



12 



3.0 











Dowzard adds: "I think the figures prove that the value of insect 

 powder as an insecticide is in proportion to the amount of ether- 

 soluble matter present. Of course, it is impossible to obtain exact 



