179 



sulphates of iron, of magnesia, of lime, and of alumine ; but if 

 the combustion be carried on with a considerable degree of rapi- 

 dity, 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 bal- 

 sam of sulphur, which is a combination of sulphur with oil. 



Yours,, &c. 



LETTER XVIII. 



BITUMINOUS FERMENTATION. ...COMPARED WITH THE OTHER 

 SPECIES OF FERMENTATION. ...BITUMENS, THE RESULT OF THIS 

 PROCESS... .PEAT, A VEGETABLE FOSSIL, THE FIRST PRODUCT aF 

 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 Connois. Chern. vol. viii. p. 243.. 



