47 
Kost investigators nov; feel th£«.t pure rather than crude 
rotenone should be reported, vvith regard to the oes'o method of 
determining purity there is sorje dif.'^erence of opinion. The 
alcohol-recovery method U_3, 63) ir, the most" u^-^ea , although it 
generally gives slightly lov/er \-alues than othnr methods. The 
titration scheine (67) ir^ay gi"V2 more accurate vJ-uos, but difficulty 
has teen experienced in apo lying it to low-rotonone roots. Polar- 
ization ( ill , 89, ISO }' is used out p-^obaoly gives values that are 
slightly too high. According to Meijer and Koolhaas (69) the 
purity determined hy melting point is generally higher than "by 
polarization. In any of th-3?e methods more nearly the correct value 
will "be obtainaa the purer the original solvate. Since the three 
methods already discuf^sed for treating the extract before crystal- 
lization .— namely , add'^.tion 01 rotenone, use of carbon, and alicali 
extraction — in general' res-.ilt iri a purer solvate, they are- to 
be recomiEpended f i oia this sta-'-cpoint as well as from that of 
improving the completeness of crystallization. Thus it appears 
from work reported by the Imperial inctitute ( 53 ) that alkali 
extraction might obviate much of the difficulty enccur.tered by 
some v.rorkers in tne ut^e of the titistion irethod with low-rotencne 
roots. 
Without doubt the procedure for the deter.Tiinatr'.on of rotenone 
that involves room-temper.atu2 e extraction with chloroform and 
crystallization from carbon tetrachloride, as exeiiiplified by the 
official A. 0. A. C. method (2), is nov the most v/idely used. 
