179 
sulphates of iron, of magnesia, of lime, and of alumine : but if the 
combustion be carried on with a considerable degree of rapidity, the 
bases only of these salts are left*. 
According to Mons. Morand, eight pounds of Scotch coal pro- 
duced thirteen ounces of a saline water, one ounce of a volatile salt, 
six ounces of dark-coloured oil, resembling petroleum in colour and 
smell, and left six pounds and a half of cinder. He suspects that the 
oil of coal obtains its colour, and perhaps its smell, from a small 
portion of sulphur which enters into its composition, since he finds 
silver is blackened by it in the same manner as by the balsam of 
sulphur, which is a combination of sulphur with oil. 
Yours, &c. 
LETTER XVIII. 
BITUMINOUS FERMENTATION COMPARED WITH THE OTHER SPE- 
CIES OF FERMENTATION BITUMENS, THE RESULT OF THIS 
PROCESS PEAT, A VEGETABLE FOSSIL, THE FIRST PRODUCT 
OF THIS FERMENTATION. 
Having supplied you with the most interesting particulars, re- 
specting the properties of bituminous substances, and the situations 
in which they are found, I shall now endeavour, aided by the ob- 
servations of those who have preceded me in this path of science, 
and by the light yielded by the later discoveries in chemistry, to 
ascertain their actual origin, and to propose a conjecture as to 
* Syst. des GVnmois. Chem. vol. viti. p. 243. 
