238 ODOROGRAPHIA. 
benzoic acid” has the peculiar fragrancelof the “ benzoin-benzoic 
acid,” it is said that the latter acid is added to the other varieties 
to give them amore “ genuine” odour, which is probable, as these 
are produced at a very much lower cost than the genuine article. 
The difference in the behaviour of the different benzoic acids 
towards potassium permanganate is much more characteristic 
when in alkaline solution than when in acid solution. If 0-1 
gram of the benzoic acid be dissolved in 3 c. c. of potash solution 
sp. gr. 1:177 at 15° C., the solution diluted with 8 c. c. of distilled 
water, 5 drops of }-per-cent. permanganate solution added, and 
the whole heated to boiling, all the benzoic acids, with the excep- 
tion of those obtained by sublimation and in the nascent way 
from Siam benzoin, yield deep dark-green liquids, in which 
gradually a brown precipitate forms, whilst the two kinds 
mentioned give immediately decolorized liquids over brown 
precipitates. The different specimens present the same appear- 
ances after standing several hours. In this way therefore it can 
be ascertained with ease and certainty whether a genuine resin 
benzoic acid is present or not *. 
A “Toluene-benzoic acid” is found in commerce which has 
been sublimed with one-fifth and sometimes with one-tenth of its 
weight of Siam benzoin to disguise its origin. This acid forms in 
white silky loose crystals, smelling strongly and very agreeably 
of! benzoin, but, when treated with potassium permanganate in 
alkaline solution in the above-mentioned proportions and with 
heat, does not behave like true “ gum ” benzoic acid. 
There are various odorous compounds artificially prepared from 
benzoic acid, besides those mentioned elsewhere under their 
appropriate headings, e. gy. :— 
Methyl benzoate. Two parts of benzoic acid, one part of 
methylic alcohol, and two parts of strong sulphuric acid are 
distilled together. The residue is redistilled two or three times 
with fresh portions of methylic alcohol, and all the distillates are 
mixed together with water. The crude methyl benzoate sinks to 
the bottom. In this state it is sometimes sold as “ Niobe 
essence.” To purify it, it is washed two or three times with water, 
dried by agitation with calcic chloride, and rectified over dry 
oxide of lead, the portion which comes over above 198° C. being 
collected apart. It is a colourless, oily fluid, with a pleasant 
* Schacht, Pharm. Jnl. [3] xii. p. 518. 
oe 
