SCIENTIFIC AND OTHER NOTES ON ESSENTIAL OILS. 19 
the mixture ceases to congeal further, allow to stand 10 minutes in the ice. At this 
point, if the mixture forms a hard mass, indicating an oil rich in cineol, 5 cc. of 
purified petroleum ether should be added, and the mass mixed well. Transfer immediately 
to a hardened filter-paper by means of a pliable horn spatula, spread evenly over the 
surface of the paper, and lay a second hardened filter-paper over the top. Outside 
the hardened filter-paper place several thicknesses of absorbent or filter-paper and 
transfer the whole to an ordinary letter-press, bringing to bear all the pressure possible 
for about one minute. Change the outside absorbent papers and press again, repeating 
the operation, if necessary, until the cineol arsenate is apparently dry and separates 
readily when touched with a spatula. 
The pressing is not complete when a hard mass remains which is broken up with 
difficulty. The method usually requires two changes of filter-paper, pressing each time 
for about two minutes. If left too long in the press, the compound may decompose. 
Now transfer completely the compound by means of the horn spatula to a glass funnel 
inserted into a 100 cc. cassia flask with neck measuring 10 cc., graduated in +/10 cc. 
Wash the precipitate into the flask with a stream of hot water from a wash-bottle, 
assisting the disintegration with a glass rod. Place the flask in boiling water and 
rotate until the compound is thoroughly broken up; add enough water to cause the 
cineol to rise into the neck of the flask, cool to room temperature and read off the 
volume; on multiplying the latter by 10, the percentage of cineol in the oil is obtained. 
In judging whether or not petroleum ether should be added, the following rule 
should be observed: Add enough petroleum ether to soften the cineol arsenate, so as 
to obtain a plastic mass; the quantity necessary never exceeds 5 cc., and decreases 
with oils containing less than 80 p.c. of cineol. The object of adding petroleum ether 
is merely to soften the hard mass and to aid in the separation of non-cineol con- 
stituents of the oil; a large excess of petroleum ether will decompose the compound”. 
According to Turner and Holmes, the arsenic acid method is applicable directly 
to all oils containing more than 50 p.c. of cineol. With lower cineol percentages, the 
precipitate is not solid enough to permit convenient handling; if the cineol content 
drops below 25 p.c., separation of cineol arsenate is not quantitative. It was found 
that the addition of an equal volume of cineol to such oils successfully overcomes 
this difficulty. In the calculation it only becomes necessary: to subtract from the 
volume of cineol, as observed in the neck of the flask, 5 cc. and to multiply the 
difference by 20*) in order to obtain the percentage of cineol in the oil. 
The authors have tested this method with three different mixtures of cineol (50, 
60, and 70 p.c.) with turpentine oil and have obtained correct results. Moreover, for 
comparison purposes they determined the cineol percentage of a number of oils with 
arsenic acid as well as with resorcinol, the test being carried out by the original as 
well as by the modified method. Unfortunately they make no mention as to the 
results obtained, so that it is impossible to see in how far these agree. As a proof that 
the arsenic acid method is superior even to the modified resorcinol method, they merely 
mention the constants of the cineol obtained in one way and the other and collected 
from several tests. For the cineol separated from the arsenic acid compound they 
found: m.p. —1°; des 0.9218; a) +0°13’, and for the one from resorcinol compound: 
m. p. — 3°; de 0.9242; a)+0°7'. These differences, which are really trifling, they 
look upon as very important and they conclude from the agreement of the first- 
1) In the Perfum. Record, 10 is given as factor. Needless to say this is incorrect, seeing that, according 
to the method described, only 5 cc. of the original oil had been treated. 
2% 
