148 Boyal Society : — Mr. Johnston on the Resins. 



obtain a resin in its normal state, is expressed by the formula 

 C 40 H 30 7 ; and the resin of Retin asphalt, also previously analysed 

 by the author, by C 40 H, 7 6 . 



The resin of ammonia, extracted by alcohol from the crude gum 

 resin, is represented by C 40 H 25 9 ; the resin of opoponax by 

 C 40 H 25 14 ; and that of assafcetida by C 40 H 26 O 10 . 



A striking relation appears between the formulas for the resins of 

 ammonia and assafcetida, the former being C 40 H 25 O y , the latter 

 C 40 H a6 O 10 , 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 formula? C 40 H 24 Hh x 7 , benzoic acid is one 

 of 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 

 (= C 10 H 27 6 ) by prolonged heating at the melting point becomes 

 C 40 H 27 3 . Ammonia resin (= C 40 H 25 O,,) by heating at 270° 

 Fahr. approaches to C 40 H 24 8 ; there being, however, a slight ex- 

 cess of oxygen, and water not being the only volatile compound 

 driven off. 



The resin of opoponax, when thus heated the hydrogen, as in 

 that of retin asphalt, remains nearly constant = C 40 H 25 14 , ap- 

 proaching to C 40 H 25 12 . The same is the case with the resin of 

 assafcetida (= C 40 H 26 6 10 ), which by prolonged heating at about 

 250° Fahr., becomes C 40 H 26 9 . These observations when multi- 

 plied are likely to assist materially in leading to rational formulae, 

 expressive of the molecular constitution of the resins. 



In reference to the general questions, with a view to the solution 

 of which the author undertook this investigation, he concludes : 



1. That the resins are not to be considered as different com- 

 pounds of one and the same radical, but rather as analogous groups 

 of comj)ounds of analogous radicals. 



