38 
BULLETIN 824, U. S. DEPAETMENT 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 four 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 ground 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 (Dowzard) . 
Sample No. 
Period of 
physio- 
logical 
test. 
Ether 
extract. 
Sample No. 
Period of 
physio- 
logical 
test. 
Ether 
extract. 
Period of 
SampteNo.jftgS 
test. 
Ether 
extract. 
1 
Minutes. 
4 
5 
5 
5 
Per cent. 
8.4 
7.6 
7.4 
6.6 
5 
Minutes. 
5 
5 
5 
5 
Per cent. 
6.4 
5.6 
5.4 
5.0 
9 
Minutes. 
7 
8 
12 
12 
Percent. 
5.0 
2 
6 
10 
3.2 
3 
7 
11 
4.2 
4 
8 
12 
3.0 
Dowzard adds: "1 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 
