70 ODOROGRAPHIA. 
the apparatus is first set in motion, the pump L begins to produce 
a vacuum during the first revolutions of the cylinder. Steam 
being now cautiously admitted into the double walls of the 
cylinder, the water is raised to boilimg at a comparatively low 
temperature, and the vapours charged with the essential oil rapidly 
pass over into the receptacle. With a 2-horse power engine and a 
boiler designed for a 5-horse power engine, five such apparatus may 
be driven at once, and the operation, including the time required for 
charging and emptying, is completed in three-quarters of an hour. 
The expressed oil of lemon contains mucilage, which is apt to 
ferment and produce cloudiness. It has been suggested by 
Dr. Bond that this can be washed out by agitating the oil with 
water in the proportion of 2 ozs. of water to 1 lb. of oil, by which 
the mucilaginous matter is removed and sinks to the bottom with 
the water. The oil can then be decanted and dried. 
Essential oils prepared by distillation with water often retain 
some of that liquid, even when they appear quite clear. The 
water may be detected by mixing the oil with several times its 
volume of petroleum-ether (the so-called benzin), whereby a 
turbidity is produced owing to the separation of globules of water. 
Oil of lemon is very apt to oxidize and resinify by contact with 
air, developing a turpentine odour, which quite unfits it for use as 
a perfume. This change can be retarded by keeping it in full 
well-stoppered bottles in a dark cool place ; also by mixing the oil 
with an equal bulk of alcohol or by pouring a little alcohol on the 
surface of the oil, which prevents its contact with air. 
It is said that oils of lemon, lavender, and others, which tend to 
resinify and acquire a terebinthinous odour, may be kept imde- 
finitely by the addition of sodium bisulphite in the proportion of 
50 grains of the salt to each pound of oil. 
Most of the commercial oil of lemon is adulterated with the cheap 
distilled oil and with oil of turpentine. 
Oil of lemons has recently been examined by Oliveri*, who 
fractionated it by distillation into three portions,—the first boiling 
between 170° and 175°°5 C., the second between 176° and 178°, 
and the third between 240° and 242°. The first was a colourless 
mobile liquid, sp. gr. 0°8867, with a very pure lemon oil odour, 
and consisted of limonen, C,,H,,, forming the characteristic cry- 
stalline tetrabromide, C,)H,,Br,, melting at 31°, and a dihydro- 
chloride, C;,H,gCl,, melting at 50°. The second fraction, amounting 
* Pharm. Journ. 27th June, 1891, p. 1172. 
