28 THE PEODUCTION OF VOLATILE OILS AND PERFUMEEY PLANTS. 



different distillations of the same plant are then united and sub- 

 jected to filtration, which process tends to separate any solid particles 

 or emulsion of oil and water. Filtration is conveniently effected by 

 pouring the oil into a glass funnel which has been fitted w^ith a fil- 

 tering medium, such as filter paper (an unsized, porous paper) or 

 cotton. When cotton is used as a filtering medium a small tuft may 

 be fitted loosely into the neck of the funnel and oil poured upon it. 

 Usually filtration takes place more rapidlj^ through cotton than 

 through paper and with much less loss. Rapidity of filtration is 

 essential to minimize the possibilities of changes taking place in the 

 oil b}^ oxidation, since the oil is more or less exposed to the action 

 of the air and light while undergoing this clarifying process. Hence 

 cotton is to be recommended. 



Just as the water that comprises the aqueous distillate is a saturated 

 solution of the oil, so the oil which floats above the distillate is satu- 

 rated with water. Usually it is of prime necessity that the moisture 

 be removed from all oils, first, because of the subsequent changes that 

 are likely to occur if moisture is present, and, second, because of 

 the turbidity which water imparts to the oil. Hence, after filtration 

 through cotton the oil should be dried by shaking in a bottle with a 

 dehj'drating substance, such as anhydrous calcium chlorid or anhy- 

 drous sodium sulphate, preferably the latter, owing to its lack of 

 action upon the constituents of the oils. The crude sodium sulphate 

 (Glauber's salts) may be dehydrated by heating it in a vessel over 

 direct heat, with constant stirring until a dry, grayish powder 

 results. But a small quantity is necessary to abstract the moisture 

 from an oil. After the oil has been dried it is again filtered through 

 a light plug of cotton. A clear and transparent oil finally results, 

 bearing in every way the appearance of a marketable oil. 



PRESERVATION. 



Many constituents of volatile oils are of such a nature that unless 

 the strictest precautions are observed in storing the oils chemical 

 decomposition takes place, causing them to change in both odor and 

 color, thereby reducing the quality and value. The esters of an oil 

 (combinations of organic acids with alcohols) are very prone to 

 decomposition, as are also many aldehydes and hj^drocarbons, which 

 either through saponification, hydration, oxidation, reduction, or 

 polj^merization become totally different substances. These chemical 

 l^rocesses are usually stimulated by the action of light and air upon 

 the oils. Therefore, in order to guard against these changes and to 

 minimize them as much as possible, the strictest attention should be 

 paid to the proper bottling and storage of the oils. 



195 



