ANALYSIS OF THE YELLOW CUM. 313 



tion. Water renders it turbid, and occasions a precipitate, 

 but a portion of the resin remains suspended, without being 

 separable either by heat or standing; so that the mixture 

 resembles a solution of gum-resin. If however it be heated 

 long enough to evaporate the alcohol, and about three 

 fourths of the liquiiJ-, almost all the resin is deposited on the 

 bottom and sides of the vessel, and the portion more mi- 

 nutely divided unites on cooling into little lufts of a lemon 

 colour. The mixture in this state has a more pleasant and 

 delicate sraeli than the resin itself, and some compare it to 

 that of storax. 



The water separated from the resin was still turbid, or a Benzoic acid 

 little coloured, and reddened vegetable blues. In order to ^^^'^'"^^^ *'^°™ 

 fix the acid it contained, 1 had recourse to the process, 

 which I employed with success in my analysis of the sub- 

 stance found in the grotto of Arc, and of castor, to obtain 

 from it the benzoic acid: I added a few drops of caustic 

 potash, and I evaporated to dryness. The residuum, which 

 resembled a kind of brown red extract, was distilled with a 

 little sulphuric acid diluted v»itb water, and toward the end 

 of the process I obtained a few small crystals, which had the 

 characteristics of benzoic acid. 



These small crystals I diffused in the acid and aromatic 

 water in the receiver, and supersaturated the mixturewith 

 lime quenched in the air. After evaporating to dryness, I 

 poured on the residuum a small quantity of cold water, to 

 take up the benzoate of lime, and separate it from the 

 sulphate and carbonate of this base, which were mingled with 

 it. Into the iiltered and concentrated liquor 1 poured mu- 

 riatic acid, which produced in it a slight precipitate of ben- 

 ?;oic acid in the form of small granular crystals. 



But I found, that the mokt simple and ready niode Rg^^ig^ ^pjg 

 of distinguishing the presence of this acid in the yellow resin of obtaining 

 was, to expose this substance to a heat sufficient to keep it ^ " ^*^' * 

 in fusion. 1 introduced the powdered resin into a very dry 

 vessel, which 1 placed on a sand-heat ; and as soon as the 

 resin was melted aqueous vapours first rose, and soon after 

 white fumes, which condensed on the sides in small shining 

 ecales, cxhibiiing all the characteristics of benzoic acid. 



As the acid is expelled, the resin first swells up: after 



which 



