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a diminishing of the water-content of the plant, the content of esterified, 
volatile acids in proportion to the total quantity of volatile acids, is largest. 
In connection with these experiments, Charabot and Hebert^) 
have also studied the influence of mineral salts on the development 
of the odorous substance in the peppermint plant, and they have found 
that the content of essential oil in the plant is increased in a marked 
degree by ammonium chloride. The sulphates of manganese and 
potassium and of ammonium appear to have a favourable effect in 
this respect. Sodium chloride and potassium chloride, on the other 
hand, exert no appreciable influence. Potassium nitrate and di-sodium 
phosphate act like the sulphates mentioned above. 
In view of the manifold adulterations of peppermint oil, A. M. Todd 2) 
lays special stress on the value which above all the determination of 
the optical rotation has, in addition to the specific gravity, for judging 
peppermint oil. 
These two constants taken together give very valuable information 
on the purity of the oils, as it would be difficult to find adulterants 
which, when added to the oil, would not alter at least one of these 
properties to a considerable extent. As the adulterators pay special 
attention to the "balancing" of the specific gravity, the alteration of 
the rotatory power frequently reveals the adulteration. 
Bennett and Parry report on some adulterations recently ob- 
served. The former^) proved an adulteration with acetine, the acetic 
ester of glycerin. As the constants given by Bennett for the oil examined 
show, the oils which have been adulterated in this manner differ very 
considerably from pure peppermint oil, and are distinguished above 
all by their very high specific gravity {d^^o = 0,964), and the excep- 
tionally high ester-content (71,2 per cent., calculated as menthyl acetate). 
In the other case which Parry and Bennett^) mention, it was 
a question of adulteration with African copaiba oil. This adulterant 
affected chiefly the rotatory power and the solubility. The oils exam- 
ined showed a rotation of — 3° to -|- 3° 30', and were insoluble in 
70 per cent, alcohol. When the alcoholic mixture was left standing, 
oily drops separated out at the bottom of the vessel. The menthol- 
content is naturally much reduced by this adulterant; Parry and 
Bennett found on the average 34 per cent, total menthol. 
In our laboratory such adulteration has not been observed in a 
single case. 
^) Compt. rend. 136 (1903), 1678. 
^) The Chemist and Drugg. 63 (1903), 369. 
^) The Chemist and Drugg. 62 (1903), 591. 
The Chemist and Drugg. 63 (1903), 154. 
