COMMERCIAL NOTES AND SCIENTIFIC INFORMATION. 59 
contents of from 3,5 to 3,9 p.c. (phenylhydrazine method). As the U.S. Pharmacopeia 
lays down 4 p.c. as the minimum limit of value, this circumstance often leads to 
disagreeable controversies with the Government officials. It is difficult to determine 
whether the low citral-content is due to abnormal conditions of the crop, or whether, 
perhaps, owing to the prevailing scarcity of oil, large quantities of distilled oils with 
a low citral content, or even terpenes, have found their way into commerce. 
We may add to the above that we have found guaranteed genuine oils to contain 
from 3,8 up to 5 p.c. of citral (phenylhydrazine method), but that lately the content 
has usually been about 4 p.c. Our previous statement (Report October 1911, 45) that 
the citral content of lemon oil ranges from about 4 to 5 p.c. may therefore be regarded 
as correct. At any rate a sample which is otherwise above reproach should not be 
rejected because its citral-content falls a little below 4 p.c. The U.S. Pharmacopceia 
should take this fact into consideration. 
A method for the estimation of the hydrocarbon-content of concentrated lemon 
oils has been worked out by E. Bocker*), who had already on a previous occasion 
published a paper on terpene- and sesquiterpene-less oils”). His method consists in 
first abstracting the citral from the oil by means of sodium sulphite, and then 
removing from it the remaining aromatic substances by washing-out with alcohol of 
which the strength has been expressly so selected, that, provided certain precautions 
are observed, the hydrocarbons remain almost entirely undissolved. Bocker proceeds 
as follows: — 
By the sulphite method the citral content is first estimated, 10 cc. of oil being used. . 
When the oil which has not entered into reaction is less than 6 cc., the estimation is 
repeated either with 5 or with 10 cc. The unattacked oil left over from the two tests 
is put together, and 5cc. of this citral-free oil is placed in a separating funnel of 
600 to 700 cc. capacity in which, immediately previously, 500 cc. of spirit of precisely 
51 p.c. by volume, cooled down to from 0 to — 2°, has been introduced. The separa- 
ting funnel is closed with a cork and the contents are repeatedly shaken, by which 
manipulation the aromatic bodies of the oil are absorbed by the alcohol, while the 
hydrocarbons are left behind almost quantitatively. The separating funnel is then 
placed in a cooling-bath of 0°, cork downwards, and left there from 6 to 10 hours. 
It is then taken out of the freezing-mixture, carefully turned back to its proper position 
and placed in a stand. When the alcoholic solution has cleared to a point at which 
only a slight film remains (which in certain conditions may take up to 2 days) it is 
drawn off to about 10cc., any oil-drops which may still adhere to the sides of the 
funnel being rinsed down with ice-cold 50 p.c. (51 p.c.?) alcohol, so that all the oil 
which has remained undissolved is brought together. When the mixture has become 
perfectly clear, the oil, being freed as far as possible from the last traces of alcoholic 
solution, is transferred to a measuring tube calibrated to */10 cc., and the vessel rinsed 
out with a little more ice-cold 51 p.c. alcohol. It is advisable to use a separating 
' funnel of which the lower part ends in a narrow, graduated tube. As soon as the 
oil is completely cleared (when the froth is very persistent a few drops of dilute 
acetic acid should be added), the volume is read off, calculated as original oil, and 
expressed in percentage-proportions. 
When a sufficient quantity of material is available, the method may be completed 
by estimating not only the quantity but also the character and the properties of the 
1) Journ. f. prakt. Chem. Wi. 89 (1914), 199. — 2) Ibidem Il. 81 (1910), 266; Report April 1910, 152. 
