106 ON THE FOOD OF PLANTS. 



" Coal not only forms the residuum of all ve- 

 " getable substances that have undergone a slow 

 " and smothered combustion, (that is, to which 

 " the free access of air has been prevented,) but 

 " also of all putrid vegetable and animal bodies. 

 " Hence it is found in vegetable and animal 

 " manures that have undergone putrefaction, and 

 " is the true basis of their ameliorating powers. 

 " If the water that passes through a putrefying 

 " dunghill be examined, it will be found of a 

 " brown colour, and if subjected to evaporation, 

 " the principal parts of the residuum will be 

 " found to consist of coal. All soils steeped in 

 " water, communicate the same colour to it in 

 " proportion to their fertility ; and this water 

 " being evaporated, leaves also a coal, as Hazen- 

 " frez and Fourcroy attest." 



And again, " Hazenfraz and Fourcroy attest, 

 " that shavings of wood, being left in a moist 

 " place for nine or ten months, began to receive 

 " the fermentative motion ; and being then 

 " spread on land, putrefied after some time, and 

 " proved an excellent manure. Coal, however, 

 " cannot produce its beneficial effects but inas- 

 " much as it is soluble in water. The means of 

 " rendering it soluble are not as yet well ascer- 

 " tained : nevertheless, it is even now used as 

 " a manure, and with good effect" 



