roa) Mr. Harcue'rr’s Odfervations.on Bituminous Subftances. 
viciffitudes of the feafons, of air; and of the weather in general, 
as well as thofe of reiterated moifture and drynefs occafioned. by 
the rife and fall of the water of the rivulet; and what feems to 
corroborate this opinion is, that the fubftance, like cork, incrufts 
the fpecies A, and appears to be only a change which has pene- 
trated deeper into the fubftance'of it in proportion to the duration 
of the caufes which I have mentioned, fo that at length the origi- 
nal fubftance no longer remains in its primitive ftate. I do not 
believe, however, that this change arifes from any alteration in the 
conftituent principles, but: ‘merely from a partial and minute dif- 
union or difintegration of the particles’ of the original fubftance, ‘as 
both {pecies melt into one’ which is’ perfealy Geille: ‘I mutt alfo 
add, that the fpecies A burns eafily, and with rapidity; but the 
{pecies B burns with fome meat and crackles as if it had im- 
bibed a quantity of water. 
[have remarked, when'the different varieties of the elaftic bitu- 
men were melted, that they completely loft the elaftic property, and 
a quantity of air or gas appeared to be difengaged, particularly from 
the {pecies B. I alfo obferved, that the fubftances which remained 
after this operation, correfponded, in refpect to confiftence, with thofe: 
which had been employed, as the following Table will fhew : 
A, No.7 and 8.... produced a_ thick liquid petroleum, not appa- 
rently different from that which is commonly 
known. 
A, No. 9. gia 83 .. produced a thicker Pets in approaching’ to 
mineral tar. . 
_ A,No. 11 and 12. produced mineral tar. | at 
B, No. 6.ssss0. produced the fame, approaching to mineral pitch. 
A, No. 13. «..0s+. produced mineral pitch. 
A, No. 14 oe I oy did. not fuffer any change, but remained as at: 
"fir, with all: the charadters of. afphaltum, 
2pblisiltios ¢ 5 From 
