taining the largest amount of oxygen of any resin hitherto ana- lysed. The resin of jalap, obtained by evaporating the alcoholic extract, and afterwards boiling it in water, is represented by C40 H34 Ojg, and in the amount of oxygen it contains is only surpassed by the resin of scammony. It is interesting to remark that these two resins in their effects on the animal economy are as nearly related as these formulae show them to be in chemical consti- tution.
The resin of labdanum, extracted by alcohol from the crude labdanum and evaporated, gave the formula 04,, H33 Og ; but this extract, softened in the air and water, took up from it a bitter sub- stance of a brown colour. After boiling in water, the pure resin is represented by C40 H33 O^.
The Berengela resin, previously analysed by the author before he was aware of the conditions necessary to be attended to in order to obtain a resin in its normal state, is expressed by the formula C40 H30 O7 ; and the resin of Retin asphalt, also previously analysed by the author, by C40 Ho^ Og.
The resin of ammonia, extracted by alcohol from the crude gum resin, is represented by C40 H^^ Og ; the resin of opoponax by C40 O14; and that of assafoetida by C40 Hog O^q.
A striking relation appears between the formulse for the resins of ammonia and assafoetida, the former being C40 H05 Oy, the latter C40 Hgg Oio, as if the latter were merely a hydrate of the former. The author considers this relation, and concludes that it is only ap- parent, and that probably in neither of the resins does any of the hydrogen exist in combination with oxygen in the state of water.
This leads the author to inquire into the general action of a slightly elevated temperature on the resins, and he concludes that in all cases when a resin in its normal state is heated a few degrees above its melting point, it begins to suffer partial decomposition, accompanied by the solution of water, and always by more or less of a volatile, generally oily compound, sometimes containing less and sometimes more oxygen than the resin which has been sub- jected to heat. In the case of some resins, especially such as are agreeably fragrant, and are expressed by the second of the author's general formulae C40 H24 + a: O^, benzoic acid is one bf the products of decomposition at a moderate temperature. Thus the resin of dragon's blood gives only a trace of benzoic acid, with water and a red volatile compound ; while the resin of benzoin gives much benzoic acid. Some resins give off vola- tile matters and diminish in weight long before they reach the fusing point ; as is the case with the resin of benzoin, of which the melting point is high. With regard to the special action of such temperatures in altering the atomic constitution of the resins, the author finds that each resin undergoes a change, probably pecu- liar to itself, and probably depending on the nature of the organic radical it contains. Thus, the formula for the resin of retin asphalt (= Cjo H07 Og) by prolonged heating at the melting point becomes ^40 H37 O5. Ammonia resin (= C40 H03 Op) by heating at 270°
