$ -2-2. DETECTION, 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. 



EXAMINATION OF THE ETHEREAL OIL. 



22. Detection and Estimation. Here, as in 11, we will first 

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

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

 small quantity. 



Like fixed oil, ethereal oil may also 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 all) and in- 

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

 several of the characteristic colour-reactions described in 142. 



AVe have now to estimate the amount of ethereal oil present 

 .as accurately as possible, without using any very large quantity 

 of material. From experiments made by Osse 1 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. (Of. 9.) If 5 cc. 

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

 he found to be sufficient. The glass dish containing the petroleum- 

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



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

 Two glass tubes are then introduced through the tubulure ; one 

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

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

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



1 Archiv d. Pharm. [3], vii. 101 (1875) (Year-book Pharm. 1876, 362). 



