Mr. Hateuetr’s Obfervations.on Bituminous Subftances. 133 
7 § 3. 
THE divifion which comprehends the fimple bituminous fub= 
ftances derived from naptha, may therefore be confidered as termi- 
nating in afphaltum ; but Nature appears to have glided on by an 
uninterrupted chain which conneéts the fimple bitumens with 
thofe which we have called compound; and this-effe& is produced 
by-the gradual increafe of the carbonie principle, and the introduc- 
tion of extraneous matter, the different quantity.of which, toge- 
ther with the greater or lefs degree of mixture or of chemical union, 
occafion’ confiderable changes in thefe fubftances, fo that they are 
gradually removed, from thofe characters which diftinguifh the 
pure bitumens. 
To form an accurate table of thefe: gradations, .it would-be. ne- 
ceffary to have comparative analyfes of the different bituminous 
fubftances,; and alfo’'to contraft the analyfes with the properties of 
thefe bodies. But at'prefent thefe analyfes, for the greater part, 
are wanting; and although at fome future time I intend to attempt 
a feries of fuch-experiments, I muft now content mytfelf with the 
obfervations and>faéts which I have been able to collecét*. From 
thefe I am of opinion, that the moft. immediate gradation from 
afphaltum (which is the laft of the fimple bitumens) into thofe 
which are.compound, takes place in the fubftance called. 
I would be underftood however to mean that the carbon is only relatively increafed, 
in refpect to the other ingredients, i in.a given quantity of thefe bitumens, and that it pre- 
dominates in proportion to the difipation of a certain portion of the hydrogen, which 
was originally neceflary to the forming of the bitumen in-conjunétion with the carbon. 
* This paper was written and read before I had feen the ingenious experiments which 
the celebrated Mr. Kirwan has publithed, in the laft edition of his Llements of Mine-~ 
ralogy.—Vide vol. ii, p. 514. is 
. 
