the characteristic Properties of Tannin. Ill 



True it is, indeed, that bitmnen 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 occasionally 

 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 hut too often 

 occasion to know) seldom to be attained, especially when 

 operations are performed on bodies whose component parts 

 are liable to an infinite series of variations in their propor- 

 tions, qualities, and mode of combination. 



Considering, therefore, that bitumen and resin afford, by 

 certain operations, similar products; that resin and bitumen 

 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 mav 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 bv 

 any of tlie known chemical processes, yet there is every 

 reason to believe that the agent employed by nature 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 coal mines except when in the vicinity of 

 salt springs, whilst on the contrary, pyrites, sulphate of iron, 

 and alum, most commonly are present*; these facts, toge- 

 ther with the sulphureous odour emitted by most of the 

 mineral coals when burned, appear strongly to evince the 

 iigenry of the latter. That this has been the case, seem* 



• Klrwan's Cfological Essays, p. 324. 



also 



