8 Dr. Mac Culloch on certain products 



I exposed a quantity of the pitch to a careful distillation through 

 water. As might be expected from what I described before in the 

 distillation of the tar, this process gave results neprly similar to the 

 former. The oily matter differed in being of a brown colour and 

 in having a greater specific gravity, and much less acid was pro- 

 duced ; the residuum was charcoal. The whole process of distiU 

 lation appears, therefore, to be a decomposition by which the pitchy 

 substance is converted into oil, acetic scid, ammonia and charcoal. 



I proceeded next to examine the oil. It has a violently pungent 

 taste and smell. It is scarcely heavier than water ; so that it sinks in 

 that fluid with difficulty, leaving generally some drops on the sur- 

 face. It is perfectly soluble in alcohol, in ether, in caustic alkali, in 

 olive oi:, and in linseed oil. It will unite neither to naphtha, nor 

 to the recent essential oils, but is soluble in the old ones. From 

 these properties, it belongs to the class of the essential oils, but ex- 

 hibits at the same time other qualities by which it is distinguished 

 from the whole of them. 



Having thus examined the most remarkable chemical properties 

 of *this substance, it will not be irrelevant to point out its differences 

 from and its analogies with those substances which it most re- 

 sembles, namely resin and the bitumens. Resin, as is well known, 

 is eminently soluble in all the substances in which this is dissolved, 

 and also in those with which this refuses to unite, even naphtha. 

 But the general analogy between essential oil, turpentine and resin, 

 is so close to that of the three substances which I have described, 

 that it will not perhaps be superfluous here to make some remarks 

 on the nature of common resin and the substances connected with 

 it, pitch, tar, turpentine and essential oil, as their history will also 

 illustrate that of the substance I am describing, and as it appears, like 

 that of the bitumens, to have been somewhat mistaken. 



