REDDf^NIVG OF LITMUS BY RESlNS. ^15 



seqiicttce several physicians undertook to make comparative 

 trials on persons of nearly similar constitutions, but they 

 have not yet observed any ditference in their purgative 

 effects. 



From the preceding analysis we may conclude, that A gnm-resin 

 scammony is a true gum-resin mingled with a little ex- ^'^^ ^ 

 tract. It is true it contains much less gum than the other 

 gum-resins, yet enough to form a milky liquor with 

 water. 



The action of the alcoholic tincture of scammony on Litmus red- 

 Htmus led us naturally to examine, whether the property of ''^'.'^^ ^7 

 reddening this blue colour were owing to an acid. INone 

 of our experiments having furnished a direct proof of this, 

 we made a comparative trial of some resins, which we sub- 

 jected to the following experiments. 



1. Sandarach. This resin is converted into a grumous Gum sanda- 

 mass by boiling in water. The tiltered liquid remains ""'ich. 

 clear; and, when evaporated to a certain point, slight- 

 ly reddens tincture of litmus; its taste is bitter; it does 



not alter infusion of violets ; it is not precipitated by 

 alcohol, or acetate of lead, which shows, that it contains 

 neither gum nor extract. It is therefore a pure resin. 



The resin thus treated with boiling water was dissolved 

 in alcohol. This tincture strongly reddened that of litmus, 

 and had no action on sirup of violets. 



Powdered sandarach was digested in alcohol, and boiling 

 water poured into the hot filtered solution, which preci- 

 pitated the resin. The filtered liquid grew turbid on 

 cooling; it had the strong smell of resin of sandarach ; its 

 taste was bitter ; and its action on the tincture of litmus 

 was so weak, that it could not be supposed to contain a free 

 acid. 



2. Mastic. This substance exliibits nearly the same Majtk^. 

 phenomena as the preceding; but the resin concretes into 

 amass in boiling, like turpentine. The water has a bitter 

 taste, and has no action either on litmus or sirup of violets. 



The resin, on the contrary, ftrougly reddens tincture of 

 litmus. 



3. Olihanum forms with hot water a thick pap, whirh ()ij|,j,,uj„. 

 is separated from the liquid with difficulty even by filtration. 



This 



