94 TANNING MATTER, &C. 



E Iments ^^^en therefore, these facts are added to that of the 

 &c. on an arti- natural mixture of resin and asphaltum which is found 

 ficlal substance ^ith the Bovey coal, we to all appearance have almost 

 ract'crs o/ tan- positive proof that thepit.coals are of vegetable origin, 

 ning matter. True it is indeed, that bitumen has never been formed 



by any artificial process hitherto devised, from the resins 

 or other vegetable substances. I have myself attempted 

 it in various ways without success, for although I occa- 

 sionally obtained products which resembled it somewhat 

 in odour when burned, and other properties, yet the 

 effects of alcohol or water always proved these products 

 not to be bitumen. 



But synthesis of natural products, although required in 

 strict chemical demonstration, is (as we have but too 

 often occasion to know) seldom to bo attained, especially 

 when operations are performed on bodies whose compo- 

 nent parts are liable to an infinite series of variations in 

 their proportions, qualities, and mode of combination. 



Considering therefore, that bitumen and resin afford by 

 certain operations similar products, that resin and bitu- 

 men are found blended together by nature, and that this 

 mixed substance accompanies a species of coal which in 

 many parts still exhibits its vegetable origin, whilst in 

 others it passes into pit-coal, we may with the greatest 

 probability conclude, that bitumen is a modification of 

 the resinous and oily parts of vegetables, produced by 

 some process of nature, which has operated by slow 

 and gradual means on immense masses, so that even if 

 we were acquainted with the process, we should scarcely^ 

 be able to imitate its effects, from the want of time, and 

 deficiency in the bulk of materials. 



But although bitumen cannot at present be artificially 

 formed from the resinous and other vegetable substances 

 by any of the known chemical processes, yet there is 

 every reason to believe, that the agent employed by na^ 

 ture in the formation of coal and bitumen has been either 

 ^ , muriatic or sulphuric acid; and when it is considered, 



that common salt is never found in coaj mines except 

 when in the vicinity of salt springs, whilst on the con, 

 trary, pyritesj sulphate of iron, and alum, most com- 

 monly 



