§ 22. DETECnON, ETC., OF ETHEREAL OILS. 21 



must be treated as above described, and the alkaloid so isolated 

 added to the extracts in which vegetable bases are to be looked for. 



J5XAMINAT10K OF THE ETHEREAL OIL. 



§ 22. Detection mid Esfmation. ^Here, as in § 1 1, we will first 

 discuss the simpler case, viz., that in which ^^he petroleum spirit 

 has removed ethereal, but no fixed oil, or at least only a very 

 small quantity. 



Like fixed oil, ethereal oil may aJso be frequently recognised 

 under the microscope as highly refracting globules, or drops of 

 irregular shape, which are soluble in cold alcohol (fixed oil dissolves 

 usually in warm spirit only, if indeed it is soluble at aJl) and in- 

 soluble in water. Some of them yield even under the microscope 

 several of the characteristic colour- reactions described in § 142. 



We have now to estimate the amount of ethereal oil present 

 as accurately as possible, without usfing any very large quantity 

 of material. From experiments made by Osse^ the following 

 method would appear to be the best. A quantity of the 

 petroleum spirit solution is accurately measured on to a carefully 

 tared glass dish, which can be closed air-tight. (Cf. § 9.) If 6 cc. 

 of the solution correspond to 1 gram of substance, 1 to 2 cc. will 

 be found to be sufficient. The glasa dish containing the petrolieum- 

 spirit solution is then placed under a tubulated glass bell-jar 



Fig. 1. 



(Fig. 1 ), A, with ground edges resting on a ground-glass plate. 

 Two glass tubes are then introduced through the tubulure ; one 

 of them (4) reaches nearly to the surface of the liquid to be 

 evaporated, the other (a) is cut off close below the cork, arid con- 

 nected with an aspirator (B), so that a current of dry air may be 



? Arohiv d. Pharm. [»], vii. 104 (1875) (Yearbook Pharm. 1876, 362). 



