259 
degree of pressure — we learn, that water may be so thoroughly 
interspersed between, and so intimately united with, the particles of 
bitumen, as to constitute a part of its mass. This, however, takes 
place in the soft bitumens only, and when these substances have once 
been deprived of the water they contain by exsiccation, they are no 
longer capable of entering into union with it ; becoming imperme- 
able to that fluid, with which every part had before been penetrated. 
Thus, in many other substances, such as the balsams, gum resins, and 
vegetable gluten, a certain portion of water enters into their original 
composition, being a necessary constituent of the substance, whilst 
existing in that form ; but when these substances become dry and 
hard, water is capable of being united with them but very sparingly, 
if at all. The Abbe Fortis, whilst describing the mine of pisas- 
phaltum, in the isle of Bua, relates that, upon breaking the drops of 
bitumen, which having exuded in a soft state, had become hard and 
brittle, he found in the centre of each a drop of clear water. That 
water exists formally in petroleum is rendered probable, by its 
being produced in a considerable quantity by the distillation of 
this substance. It must indeed be allowed, that, in the operation 
'of distillation, such a new combination of the principles of which 
the petroleum is composed may take place, as may occasion the 
formation of water ; the hydrogen and oxygen thus uniting, whilst 
the carbon is left in the residuum contained in the retort : but that 
water may exist in, and form a part of, the original substance, there 
does not appear to be the least reason to doubt*. 
* That water may exist in an intermediate state, between that resulting from the actual 
combination of the principles which constitute water and their state of complete separation, 
does not appear to be improbable. In siliceous and other hard bodies, capable of being 
reduced to a pulverulent form, and in no other way manifesting the least trace of it, its pre- 
sence is detected by distillation. From the observations of my ingenious neighbour, Mr. 
Hornblower, it appears, that the current of air from an hydraulic bellows produced a con- 
siderably greater effect, in augmenting the intensity and brilliancy of the fire to which its 
