Holde, after a careful trial of the various processes for detecting
the above adulteration, gives the preference to Renard's, which he
describes as follows:
Ten grms. of the suspected oil, after being saponified, and the fatty
acids separated by hydrochloric acid, are dissolved in 90 per cent.
alcohol, and precipitated by sugar of lead. The oleate of lead is
separated by ether, and the residuum, consisting of palmitic and
arachic acids, is decomposed by hydrochloric acid. The fatty acids are
dissolved, with the aid of heat, in 50 c.c. of 90 per cent. alcohol.
The arachic acid which separates after cooling is filtered out and
washed, first with 90 per cent. and afterward with 70 per cent.
alcohol. It is then dissolved in hot alcohol, and the solution
evaporated in a weighed saucer. The weight of the residuum, after
taking into account the acid dissolved in the alcohol, equals the
whole amount of arachic acid contained in the oil; the melting point
of this residuum should be 70° to 71° C. With this process the author
has always been successful; but when the olive oil contains not more
than 5 to 10 per cent. of peanut oil, it is necessary to make the test
with 40 grms. of the former, otherwise the melting point of the
arachic acid cannot be estimated. Furthermore, the acids which are
separated from the lead salt by hydrochloric acid must be
recrystallized repeatedly with 90 per cent. alcohol, until the melting
point ceases to rise, in case the latter is not found to exceed 70° C.
at the first estimation. When peanut oil is present, the melting point
will always be above 70°.--_Chem. Zeit._
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