:\Cr2
In a succeding letter, xxv. our author applies the princi-ples he had established, as mentioned in the early part ofthis division of the present article, on the produce of bitv-mens, &c. to the formation of such vegetable matter whichhe believed was concealed by the superincumbent strata ofthe earth, so formed as lately mentioned, from the consoli-dating matter previously supposed to be deposited over it.This vegetable material concealed and secured, as in analembic, or ecjual to a chymical recipient, with a quantityof moisture, either foreign or indigenous, is now believedto be properly secured for perfecting the process of bitumi-nization, which it is gradually suffering; a chief previouslystipulated principle being the secure exclusion from atmo-spheric air, which, with the retention of the vapours pro-duced in bituminization, is believed to be effected by thevarious strata of minerals and stoney earths which cover thevarious depositions. Since the change of colour from thebrown of petroleum to the black of jet is found to be theconsequence of a proper saturation with carbon, one of itsconstituent principles, of conjoined hydrogen and oxygen,conformably with these operations, the materials are believedto have been then in the most favourable situation. Because,it is said, that during the formation of coal, the bitumen isthoroughly pervaded by other substances, impregnated withoxygen, from which, by a superior power of attraction, thecarbon has power to detach it, and then to engage it incombination with itself.
From what has already appeared, we behold, that whilstdiscussing the formation of bitumen, a chief operation wasnoticed with respect to its different states of fluidity, irispis-sation, and induration. With respect to coal, it is nowobserved, that its formation is regarded as the most im-portant end of the bituminizing process. Thus constituted,he says, it would be reasonable « priori to conclude, that thelaws of nature would decree that the substance, to undergothis necessary change, should in general be so disposed asto secure to it the desired effect in every stage of the opera-tion. Should the circumstance of coal having existed in a stateof fluidity, that is, pure bitumen, be again asserted, he showsits utter inapplicability for the purposes to which coal isapparently adapted. Hence he deduces the necessity of itsultimate induration, which is effected, as weli as its colour,by the operations of the various airs inherent in the matter,or else found to pervade its neighbouring particles as beforeadduced. That this substance was produced as previouslypremised, he reverts to the still existing traces of formerfluidity, which are now to be traced in the masses of coal,