38 SUBSTANCES SOLUBLE IN ALCOHOL. 



IV. 



EXAMINATION OF THE SUBSTANCES SOLUBLE IN ABSOLUTE 

 ALCOHOL. 



RESINS, TANNINS, BITTER PRINCIPLES, ALKALOIDS, 

 GLUCOSES, ETC. 



47. Extraction. The residue of the substance under examina- 

 tion after exhaustion with petroleum spirit and ether (cf. 36) is 

 removed from the filter, dried at the ordinary temperature, and 

 treated with 10 cc. of absolute alcohol for every gram of original 

 substance. After the lapse of five to seven days the alcohol lost 

 by volatilization is replaced, and the whole well shaken. It is 

 then filtered through the same filter that has been used for the 

 previous operations, any evaporation of alcohol being prevented 

 as carefully as possible. A measured quantity of the filtrate is 

 next evaporated in a tared platinum dish and dried until the weight 

 noted is constant. It is then incinerated, and the ash deducted froi 

 the weight of the dry substance. After having thus estimated 

 the total organic matter insoluble in petroleum spirit and ether, 

 but soluble in alcohol, the residue on the filter may be wash* 

 with absolute alcohol, and the washings, with the remainder of 

 the filtrate, concentrated. This may best be done by distilling 

 in a flask, under diminished pressure. The liquid remaining 

 after distillation is poured into a glass di sh, and allowed to eva- 

 porate, at the ordinary temperature, over sulphuric acid. 



48. Estimation of Portion Soluble in Water. The dry residue 

 thus obtained is first treated with a measured quantity of water. 

 To ascertain the amount soluble in this menstruum, as well as in 

 alcohol, a measured quantity of the solution is similarly evapo- 

 rated, dried at 110, and weighed. 



The remainder of the aqueous extract is reserved for the 

 experiments detailed in 49, 50, 70 ; that which is insoluble ii 



