132 Mr Harener’s Obfervations on Bituminous Subftances. 
MOUNTAIN or MINERAL PITCH—Bitumen Matrua.,. 
Tue mineral pitch ‘much refembles common pitch, and, when: _ 
heated, emits a {trong unpleafant odour, like the former fubftance. 
When the weather is cold,. it may be broken, and then exhibits,, 
internally, a glafly luftre ; ; but when warm, it is foftened, and pof- 
fefles fome tenacity, It is however fufceptible of a fuperior degree 
of induration, and then becomes 
ASPHALTUM—Birumen AsPpHALTUM—PETROLEUM 
, ENDURATUM. 
Tus is a lioht, brittle fubftance,. of a brownifh. black,.or black. 
When broken, it fhews a conchoidal fra€ture with a glafly luftre. 
It has little of the bituminous odour, unlefs it is rubbed or heated. 
It eafily melts, is very inflammable, and, when pure, burns without 
leaving any afhes.. ' aM 
In this manner, naptha, by infpiffation, alles aceeiheely through 
different ftates until it becomes afphaltum, which appears to be.the 
ultimate. degree of induration which the pure bitumens derived 
from naptha can receive. 
I have at this time fpecimens before me which prove thefe 
gradations ; and I have feen, a remarkable inftance in a bitumen 
brought from the Ifland of »Trinidad, which exhibits: mineral. tar 
palling into mineral pitch, and laftly into afphaltum *. 
‘ § 3. 
* The progreflive changes of naptha into petroleum, mineral’ tar, mineral pitch, and 
afphaltum, appears to be caufed by the gradual diffipation of part of the hydrogen of 
the bitumen, and the confequent development or difengagement of carbon. Hence, I 
am inclined to believe, arife the changes of colour, the degrees of infpiffation, and. 
the aeaee proportion of carbon found in thofe: fubftances ‘by chemical analyfis. 
fe T would 
