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bined action of a portion of caloric ; and, secondly, by conveying 

 to every point of the vegetable substance the leaven of the bitumi- 

 nous fermentation ; by the active energies of which fermentation 

 the whole mass of solid wood is made to undergo an actual conver- 

 sion, and to pass from the state of wood to that of bitumen. 



This particular species of fermentation may be illustrated, by 

 considering the phenomena which result from vegetable matter be- 

 ing placed in such circumstances, as we have assumed necessary to 

 the production of this fermentation, excepting only that of not 

 being in a subterranean situation. Should we find that vegetable 

 matter thus disposed undergoes a somewhat similar fermentation, 

 producing a change approximating to that which takes place in 

 what I have termed the bituminous fermentation, we shall have 

 another presumptive evidence of the propriety of distinguishing 

 the process by which peat is formed, as a species of fermentation. 



The situation in which we find vegetable matter thus disposed, and 

 in which the effects are immediately under our own examination, is 

 that in which the various species of grass, Sec. are so closely stowed 

 together, and in such quantity, that the weight and thickness of the 

 superior layers must totally prevent all access of the external air, 

 and any escape of the separated gases. You must have already 

 perceived, that I here refer to the process employed in hay-making; 

 and you well know, that when this operation is conducted accord- 

 ing to the wishes of the farmer, that the saccharine fermentation, 

 or a fermentation nearly resembling it, only takes place ; and the 

 grass is changed into hay, which possesses a peculiar fragrance and 

 sweetness. But should the grass, at the time it is heaped together, 

 unfortunately retain too much water, very different effects will fol- 

 low: heat will be rapidly evolved, and a dense vapour will be seen 

 to exhale from the mass. If the process be stopped in this stage, 

 the mass of vegetable matter will be found to have acquired a very 

 dark brown colour, and a glazed surface, and to emit a strong 



