134 <Mr.Harcuerr’s Odfervations on Bituminous Subjtances, 
JET. 
Jet is a fubftance well known to be of a full black, fometimes 
however inclining to ‘brown. It is confiderably harder and lefs 
brittle than afphaltum. It breaks with a conchoidal fracture, and 
the internal luftre is glaffy. It has no odour except when heated, 
and it then refembles afphaltum. It melts in a {trong heat, ands 
when burned, leaves an earthy refiduum. ; 
Wallerius confidered jet as afphaltum which had become aga 
rated by time, and Mr. Fourcroy is of the fame opinion*. Others 
again have arranged it with the varieties of coal}. Iam inclined 
however to believe, that it is neither afphaltum nor coal, but 
an intermediate fubftance which may be regarded as the firtt 
gradation from the fimple bitumens into thofe which are compound, 
The matter of afphaltum undoubtedly enters into it ina large pro- 
portion, and has confequently ftamped feveral of its characters 
‘upon it; but the increafe of carbon, and of the extraneous or 
“earthy matter which is intimately mixed or rather combined with 
‘it, has had fo much influence, that the characters of coal 
are alfo in fome meafure apparent, and are rendered the more 
ftriking by the fimilarity of certain local circumftances which 
attend thefe two fubftances. The charaéters, of coal are however 
by no means fully eftablifhed in jet, but from this we pafs imme- 
diately to another, in which thefe characters cannot be queftioned, 
This is the fubftance called 
CANNEL ‘COAL, 
which is of a full black, of a fmooth, folid, even'texture ; it breaks 
in any direction, and the tranfverfe fraGture is conchoidal. It 
* Elémens d’Hift. Nat. et de Chimie, tom. iii. p» 456: 
“+ Widenmann’s Handbuch der Mineralogie, p. 628. 
burns 
