Ht'sTOliY OF PiTCOAL. 153 



ward the end to become a uniform mass, no#to be divided 

 without labour. 



All pitcoals iii general <^ive out more cr less sulphurous Yield sulphur- 

 acid toward the end of their combustion, which is owing^ to ^"^ acid, 

 pyrites. At first I supposed, that they contained a peculiar 

 compound of sulphur and carbon ; but all that I passed 

 through nitric acid, to free them from pyrites^ burned to 

 the end without emitting the slightest smell of sulphurous 

 acid. 



The oily product of these coals varies greatly in consist- Oily product 

 ience; it is more or less fluid, and a direci experiment is al- si^tence" '^^^^ 

 ways necessary, to ascertain how much thick oil, or tar, it 

 will afford. Is this tar really more preservative, ^.nd better Should be far- 

 adapted to retard the spontaneous oxidation of cordage, and ^^^er examined, 

 the rigging df ships, than that of resinous wood? This has 

 been asserted, but should it not be farther examined ? 



The light oil separated from it is succinated, and not lin- Light oil, 

 pleasant. It is readily turned brown by the air. No parti- 

 cular use for it is known. 



The aqueous product c6ntair<s carbonate df ammonia, but Water contains 



in small quantity. I did not find in it any vinegar, but I carbonate of 



T •' ^ , , -^ . ammonia, and 



could wish to Examine this again ; particularly as I find in succinic acid. 



my notes, that I separated a little succinic acid from it by 



treating it with the muriatic. 



The gas is an oily hidrogen, that burns with a white flame. Gas, oily'hi- 



^hich limewater diminishes very little, because the ammi)nia[ fi'oge", with 



. . , verv little car- 



retains almost all the carbonic acid. bonic acid. 



Naturalists, reflecting on the similitudes that analysis per- Coal supposed 



ceives between the composition of ve^retables and that of *,*^^^ P*"*^^^^^*^ 



, . 1, 1 1 It ffO'^'^ vegeta- 



pitcoal, have pretty generally supposed, that coal may have bles. 



been produced by heaps of fern, polypody, reeds, jind aqua- 

 tic plants destroyed, the impressions of which are retained 

 by the adjacent strata ; or even by trees, and their frag- 

 luents, such as those which certain rivers by their inunda- 

 tions sweep away from the earth ; and that the sea has bro- 

 ken them by its agitation, and accumulated them in the 

 basins, fr«m which we at present extract them. Etit the 

 mechanism, and even possibility of these operations, simple 

 as they are in appearance, are exposed to innumerable diflfi- 

 culties, when we examine them in detaiU 



M 2 IFor 



