36. EXTRACTION OF RESINS AND THEIR ALLIES. 31 



III. 

 EXAMINATION OF THE SUBSTANCES SOLUBLE IN ETHER. 



RESINS AND THEIR ALLIES. 



36. Extraction. After the examination of the substances dis- 

 solved in petroleum-spirit has been carried as far as possible, 

 the residue (cf. 9), thoroughly washed with the menstruum, 

 should be removed from the filter (which is to be kept) dried at 

 the ordinary temperature, and then macerated for seven to eight 

 days with pure ether. It is advisable to use the same vessel that 

 has been employed for the treatment with petroleum spirit. If 

 it has been well washed there is no necessity for being minutely 

 particular to bring the whole of the residue on to the filter. The 

 same vessel should, if possible, be reserved for the extraction 

 with alcohol, to be described in 47, and the filtration effected 

 through the same filter that has already done duty for the 

 petroleum spirit and ether extracts. I allow the ether destined 

 for this purpose to stand for several weeks over porous chloride 

 of calcium, and then rectify it after carefully separating the 

 calcium salt. To obtain constant results in such analysis it is 

 necessary to have the ether as free as possible from water and 

 alcohol. Ordinary commercial ether would, for instance, extract 

 a portion of the tannin (sometimes more, sometimes less) from 

 parts of plants containing that substance, whilst ether, purified as 

 described, does not usually produce this effect. As it is not well 

 possible to remove the whole of the tannin with commercial 

 ether, I prefer to refrain from extracting any of it with that 

 menstruum, and remove the whole subsequently with alcohol. To 

 attain this end I avoid the employment of a high temperature in 

 extracting with ether. Indeed, I am of opinion that in the course 

 of the analysis of plants, it is better in the majority of cases to 



