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water, and therefore communicates no taste to it. Being heated in 
a retort, it is decomposed, and yields a bituminous and empyreu- 
matic water, carbonic acid, and a concrete volatile salt ; a carbo- 
naceous residuum being left. When placed on burning charcoal, or 
in a heated crucible, it burns like combustible vegetable matter ; 
leaving a greyish white matter, which has all the characters of alu- 
mine, mixed with a small portion of lime. This substance, therefore, 
appears to be composed of alumine, bitumen, a small portion of lime, 
and a peculiar acid, which resembles in many of its properties the 
oxalic acid, but dilfers from it materially in others. This acid is 
decomposed very speedily by heat, evaporating in a dense smoke : 
and by distillation yields a considerable quantity of carbonic acid. 
AVhen the constituent parts of this substance are considered, with the 
situation in which it is found, and the substances with which it is 
associated, there can be but little hesitation in admitting it to be 
produced by the subterranean decomposition of vegetable matter, 
and therefore to belong to that class of natural productions of which 
we are here treating. The appearance which this substance presents 
may be pretty correctly known by reference to the representation 
of it, Plate I. Fig. 2. 
The bituminous name of jet is indisputable, it being plainly 
evinced both by its chemical and physical properties. Indeed it 
often manifests so exact a resemblance, in every respect, except in 
its colour, to amber, as to have occasioned it to be named, as has 
been already remarked, black amber. The blackness which distin- 
guishes it has never yet been satisfactorily accounted for, and in- 
deed olfers to our consideration a question difficult of solution. 
The learned Wallerius and the celebrated Fourcroy have contented 
themselves with considering jet merely as indurated asphaltum , 
whilst others have been satisfied with describing it, with coal,^ as 
bitumen, altered by exposure to the action of certain mineral acids. 
Mr. Hatchett, indeed, in that most valuable paper to which I have 
