468 Scientific Intelligence. [June, 



me into the notion that hydrogen was a constituent of indigo. 

 It is obvious that this resinous substance is easily got rid of by 

 disesting; the indigo recovered from the indigo vat in a sufficient 

 quantity of alcohol. 



VII. Common Rosin. 



Modern chemists have very much neglected the characters of 

 resinous bodies, though the science is now sufficiently advanced 

 to enable us to discriminate them with precision from each other, 

 and even to determine their constituents. I intend, therefore, 

 occasionally to introduce into the Annals of Philosophy an 

 account of the experiments which I have occasionally, and at 

 long intervals, made upon these bodies, both with respect to 

 their characters and composition. I shall begin with common 

 rosin, as constituting the common type to which all the others 

 have been referred. 



Common rosin, as purchased in the shops, is a semitransparent 

 brittle resin, of a yellow colour. Sometimes it has a slight 

 smell of turpentine, and sometimes is nearly destitute of all 

 smell. In the hrst case, it is probably contaminated by some 

 oil of turpentine. 



The specific gravity of common rosin I found to be 1*080. 

 Alcohol, of the specific gravity 0-835, dissolves the eighth part 

 of its weight of it at the temperature of 60°. The solution is 

 yellowish, and perfectly transparent. When exposed to a mode- 

 rate heat, the alcohol flies off, and leaves the rosin in the state 

 of a semitransparent mass, of a much darker-brown colour than 

 before the solution, and exactly similar in appearance to rosiu 

 that has been kept for some time in a state of fusion. 



When common rosii;i is heated to the temperature of 156°, it 

 becomes viscid, and of the consistence of common turpentine. 

 As the heat increases, the rosin swells up, and becomes filled 

 with bubbles. This is owing to a quantity of water, and proba- 

 bly also of oil, which is separated from it by the action of the 

 heat. When heated to the temperature of 276°, it becomes 

 quite fluid ; and if it be kept a sufficient time at that temperature, 

 it loses all its water, and remains in the state of a reddish-yellow 

 liquid. When allowed to cool, it concretes into a reddish- 

 yellow rosin ; much darker coloured than before, and obviously 

 altered in its constitution. 



To determine the constituents of rosin in the state in which we 

 find it exposed to sale, I heated a grain of it in the apparatus, 

 which I have described in a former paper, with peroxide of 

 copper. The mean of two experiments, which scarcely diftered 

 from each other, gave the following results : 



5 cubic inches of carbonic acid . . — 0"6324 gr. carbon 

 1-05 gr. of water = 0'1164 gr. hydr. 



Total = 0-7488 



Deficiency = 0-2512 gr. 



