354 
MR. JOHNSTON ON THE CONSTITUTION OF THE RESINS. 
comparing the atomic constitution of the resin before and after being heated. Thus 
the fifth analysis of the resin of opoponax gives 
Carbon 66'38 4 atoms. 
Hydrogen 6*79 25‘09 atoms. 
Oxygen 26*83 12’4 atoms, 
100 
by which we see that the oxygen diminishes much more rapidly than the hydrogen ; 
that water or a carbo-hydrogen are not alone given off, but along with these, if evolved 
at all, there is evolved another substance also of more complicated constitution. 
XVI. Resin of Assafcetida. 
I. The assafoetida of the shops loses little in bulk when digested in cold alcohol of 
0*83, but it gives a pale-yellow solution, from which, by evaporation, a resin of the 
same colour is obtained. This resin has the characteristic odour of the gum resin, 
and the property which the natural product also possesses of becoming purple when 
exposed to the sun’s rays. Laid as a thin coating upon paper, the pure resin is much 
more sensible to the sun’s rays than the resin of guiacum, and affords a much more 
beautiful colour. It is readily and completely soluble in cold alcohol and ether. 
Like many other resins it must be heated for a length of time before it becomes hard 
and brittle, and reaches its normal state. By this prolonged heating it acquires a 
darker and brownish colour, and is easily decomposed if the temperature be raised 
much above 212° Fahr. As the temperature rises, the resin froths up very much for 
some time, giving off a strong garlic odour ; it then flows quietly till the heat is 
again increased. When completely burned, the resin employed in the following 
analyses left 0*18 per cent, of brown ash. 
1. A small portion of the solution was evaporated and heated in the state of a thin 
film for forty-eight hours to 180° Fahr., and afterwards for six hours to 212° Fahr. 
The resin was brittle. 
5*79 grs. gave C = 14-52, and H = 3-93 grs. 
2. A second portion was evaporated and digested for many hours at 212° Fahr. 
8‘19 grs. gave C = 20*66, and H = 5-55 grs. 
3. Of the same, a portion heated twelve hours longer, and from that cause a little 
darker in colour, 
6 - 02 grs. gave C = 15*32, and H = 4*14 grs. 
4. Of the same mass, a portion was heated very gently in a platinum capsule over a 
lamp, and kept in a state of fusion for an hour. The heat was not sufficient to drive 
off any visible fumes, but the odour of the resin became much weaker. In this state 
6*56 grs gave C = 16*82, and H = 4*475 grs. 
