^ 23, 24, 25. DISTILLATION OF ETHEREAL OIL. 23 



of tlie ethereal oil by evaporation, whether the residue is now 

 still completely soluble in petroleum spirit. Eesins which, in a 

 state of purity, are not dissolved by petroleum spirit, may be taken 

 into solution by means of ethereal oil, just as fixed oil carries 

 with it alkaloids and chlorophyll; they are left undissolved on 

 again treating with petroleum spirit the residue freed from 

 ethereal oil. After having removed by this solvent the fixed 

 oil, etc., that has been simultaneously extracted, the resin may be 

 weighed alone (§ 146). 



Of course it is advisable to repeat the experiments described in 

 §§ 22, 23 several times, and take the mean of the results. I need 

 scarcely say that this method of determining the total ethereal oil 

 does not guarantee any absolute accuracy, but as it is the only 

 one we have at our disposition it might, for the time at least, be 

 deserving of some notice. With less volatile oils, cinnamon, 

 clove, etc., it has yielded very satisfactory results, but less so Avith 

 terpenes, such as oil of lemon and turpentine. 



§ 24. Distillation of Larger Quaniities of Oil. — If a further insight 

 into the composition of the ethereal oil is desired, a larger quantity 

 must be prepared from 5 to 100 kilograms of material. For this 

 purpose distillation in a current of superheated steam is to be 

 recommended, the material having been if necessary previously 

 comminuted and soaked in water. In order that the steam may 

 thoroughly penetrate it the apparatus should be packed Avith 

 alternate layers of material and straw. A distillate consisting of 

 essential oil and water will be obtained which may be separated 

 from one another in burettes or Florentine flasks. It should not, 

 however, be forgotten that many ethereal oils are tolerably easily 

 soluljle in water, and a small quantity of petroleum spirit of low 

 boiling-point should therefore be shaken with successive portions 

 of the aqueous distillate. The petroleum spirit is allowed to 

 evaporate in a current of carbonic acid in the apparatus described 

 in § 22, and the residue added to the oil separated from the distil- 

 late (§ 137). 



§ 25. Examination of Aqueous Distillate. — After separation of 

 the oil, the action of the watery liquid on litmus should be 

 tested. It will be frequently found to possess a distinct acid 

 reaction, and contain furmic, acetic, or other volatile acids of the 

 fat-acid series. In such a case the higher acids in the series 

 may be removed by shaking with ether or petrolemn spirit. To 



