52 SUBSTANCES SOLUBLE IN ALCOEOL. 



purify abitter principle dissolved by water from the ethereal extract, 

 than one obtained in a similar manner from the alcoholic extract, 

 since the latter contains glucoses and tannins, which are insoluble 

 in ether. Apart from the treatment with chloroform and other 

 solvents which I have just described, another method of purifica- 

 tion may in this case be adopted — viz., evaporation of the aqueous 

 solution, extraction with the smallest possible quantity of absolute 

 alcohol, and precipitation of sugar, etc. with ether. 



§ 59. Separation of Tann'm. — Tannic acid, when present in solu- 

 tion, together with bitter principles, etc., may frequently be 

 removed by digesting the aqueous infusion Avith oxide or hydrate 

 of lead. If salicine (cf. § 167), for instance, is to be separated 

 from tannin, the aqueous infusion may be mixed with oxide of 

 lead, evaporated to dryness on the water-bath and extracted with 

 alcohol. Basic acetate of lead may also be occasionally used, when 

 a bitter principle is to be separated from tannin, vegetable acids, 

 albuminous matter and the like. Of course, it must have been 

 i:)reviously ascertained that the bitter principle in question is not 

 precipitated by lead ; shoidd that be the case, it may sometimes be 

 isolated by decomposing the lead compound with sulphuretted 

 hydrogen. By combining a bitter principle with lead a separa- 

 tion may sometimes be effected from sugar, etc. This method is, 

 however, inai)plicable if tannic acid be present, when it will often 

 be found advisable to precipitate vegetable acids, tannin, etc., by 

 neutral acetate of lead before throwing down the bitter principle, 

 etc., with the basic salt (§§ 51, 162). 



§ 60. Separation of Lead Precipitate. — If such compounds of lead 

 with bitter principles, glucosides, etc., are to be washed with 

 water, it is very advisable to effect this as rapidly as possible by 

 decantation. Such precipitates often block a filter, or form, by 

 contraction, channels through which the wash-water runs off with- 

 out penetrating the precipitate. If the use of a filter is neces- 

 sary, repeated suspension in water and filtration is advisable. 

 The washing of such precipitates should not be continued too 

 long, as they usually undergo decomposition during the process 

 and yield the Ijitter principle to the Avash-water. The presence 

 of carbonic acid in the water used for washing is specially to be 

 avoided. 



Decomposition.— T\iG decomposition of these precipitates is 

 usually effected Ijy sulphuretted hydrogen, which, however, does 



