130 BESIXS, BIT TEE PRINCIPLES, ETC. 



1. For the determination of the ethereal oil petroleum spirit may 

 be used as a solvent.^ (See §§ 9, 22, 23, 138.) But, as elsewhere 

 observed, part of the resin will also be dissolved ; the residue 

 obtained by evaporating at the ordinary temperature till the 

 weight is constant must therefore be heated to 110° or 120°, and 

 the percentage of ethereal oil calculated from the loss. The 

 amount of resin dissolved by the jDetroleum spirit, which is thus 

 simultaneously ascertained, may be of use in estimating the value 

 of different varieties of a resin or in detecting adulterations (in the 

 case of copal, the better the quality of the resin the smaller the 

 percentage of non-volatile substances soluble in petroleum spirit). 

 The mixture (of ethereal oil and resin) obtained by evaporating 

 the petroleum-spirit solution frequently yields colour-reactions with 

 the reagents mentioned in § 142, 



2. The residue insoluble in petroleum spirit is treated with ether 

 and the substances dissolved estimated. It should be ascertained 

 if ether takes up all the resin insoluble in petroleum spirit or if a 

 further portion is removed by subsequent treatment with alcohol. 

 Gum-resins will of course always leave a residue insoluble in 

 ether, consisting of sugar, gum, salts, etc. The ethereal solu- 

 tion should be tested as to its miscibility with alcohol and the 

 residue after evaporation for ' colour-reactions as mentioned 

 in 1. 



3. The estimation of substances soluble in alcohol, both in the 

 original drug and after treatment with ether, together with the 

 qualitative examination of the solution, may likewise yield results 

 of some value. In the case of gum-resins sugar is one of the prin- 

 cipal substances extracted by alcohol. (See §§ 70, 83 et seq. ; 200 

 ei seq.) It should be ascertained whether a turbidity is produced 

 by adding ammonia, ether, or alcoholic solution of acetate of lead 

 to the spirituous extract from the original resin. 



4. If a gum-resin is under examination, water will remove gum 

 (§§ 73 et seq.; and 193 c^ seq.) and certain salts from the residue 

 after treatment with alcohol. Note should be taken if a gum 

 swelling, but not dissolving, in water is present. (See §§ 103 and 

 193 d seq.) 



5. Important results may also be obtained by treating the 

 original resin with chloroform, ether, or saturated aqueous solution 



' The resin should be rubbed down as fine as possible with powdered glass, 

 and then macerated with petroleum spirit. 



