the charactei'isiic Properties of Tannin. 1 1 3 



Every circumstance seems, therefore, to support the opi- 

 Tiion of those who consider the pit coals as having been 

 formedj in the humid way, principally from vegetable bo- 

 dies, and most probably by the agency of sulphuric acid ; 

 and allowing that animal substances may also have contri- 

 buted ty the production of coal, yet this would not militate 

 against the above-mentioned opinion, as the effects produced 

 upon them by that acid would in all the essential points be 

 perfectly similar*. 



An 



have been formed) were previously deprived of alkali by simple lixiviation 

 during their immersion in water. But in page 157 of this paper I have shown 

 that the submerged oak of Sutton, although deprived of its tannin, still re- 

 tained its potash, which certainly would not have been the case if the latter, 

 like the former, could have been separated from the wood by mere solution. 

 When wood is reduced to ashes the alkali becomes completely denuded by the 

 destruction of the woody fibre, and consequently may be immediately taken 

 up by water ; but when wood is converted into coal in the humid way by 

 means of an acid, then it seems to me that two effects take place; for the iu» 

 timate combination of the alkali with the woody fibre becomes in a great mea- 

 sure destroyed by the carbonization of the latter, whilst a simultaneous action 

 arises in the affinity between the acid and the alkali ; so that if coal has been 

 formed by such mears, the alkali must have been separated from the wood in 

 the state of a dissolved neutral salt. 



* From the nature of the experiments which have been related in this 

 paper, I have unavoidably been induced to notice concisely the different opi- 

 nions on the formation of coal by the humid way; but I did not intend to 

 have mentioned any of those which have been brought forward in favour of 

 the immediate or indirect action of fire, as I only wi:.hed to express m.y senti- 

 ments respecting the nost probable of the former opinions. 



Since, however, this paper was written, and parti; re;;d before the Royal 

 Society, 1 have been favoured by sir James H.ill with a copy bf his paper» 

 entitled " Account of a Series of Experiments showing the Effects of Com- 

 pression in modifving the Action of Heat;" and I am fully of opinion that 

 the scientific world has not for a long time received any communication 

 of more importance, or in which more .iccuracy, ability, and perseverance 

 have been displayed. The effects which sir Jarnes Hall has produced on car- 

 bonate of lime by heat acting under compression, cert:.inly remove a great, 

 and at one time apparently lusur.Tiounuihle, ob;.tacle to the Huttonian or Plu- 

 tonian theory ; and if they do not solve the grand geological problem, they 

 must, even in an innulatcd point of view, be allowed to have opened a new 

 and unexplored field of research in chenwstry as well as in geology. 



In the eighth section of this valuable paper llie audior has given an account 

 of some experiments made on leather, horn, and lir sawdust, fri>m which he 

 obtained coal which burned with flame, and which apparently resembled 

 «omc of the mineral coals. In one case, also, he ubtaiueU a subitance whictv 



Vol.'J7. No. 106. M«ff/i 1807. H in 



