BOOK II. OPERATION OF MINERAL MANURES. 243 



If there are seeds carried out in the dung, they certainly will germinate ; but it is seldom 

 that this can be the case to any extent ; and if the land is not cleansed of weeds, any 

 kind of manure, fermented or unfermented, will occasion their rapid growth. If 

 slightly fermented farm-yard dung is used as a top-dressing for pastures, the long 

 straws and unfermented vegetable matter remaining on the surface should be re- 

 moved as soon as the grass begins to rise vigorously, by raking, and carried back to 

 the dunghill : in this case no manure will be lost, and the husbandry will be at once 

 clean and economical. In cases when farm-yard dung cannot be immediately applied to 

 crops, the destructive fermentation of it should be prevented as much as possible : 

 the principles on which this may be effected have been already alluded to. The surface 

 should be defended as much as possible from the oxygen of the atmosphere ; a compact 

 marl, or a tenacious clay, offers the best protection against the air ; and before the dung 

 is covered over, or, as it were, sealed up, it should be dried as much as possible. If the 

 dung is found at any time to heat strongly, it should be turned over, and cooled by 

 exposure to the air. 



1161. The doctrine of the proper application of manures from organised substances, 

 offers an illustration of an important part of the economy of nature, and of the happy 

 order in which it is arranged. The death and decay of animal substances tend to 

 resolve organised forms into chemical constituents ; and the pernicious effluvia disengaged 

 in the process seem to point out the propriety of burying them in the soil, where they are 

 fitted to become the food of vegetables. The fermentation and putrefaction of or- 

 ganised substances in the free atmosphere are noxious processes ; beneath the surface of 

 the ground they are salutary operations. In this case the food of plants is prepared 

 where it can be used ; and that which would offend the senses and injure the health, if 

 exposed, is converted by gradual processes into forms of beauty and of usefulness ; the 

 foetid gas is rendered a constituent of the aroma of the flower, and what might be poison 

 becomes nourishment to animals and to man. 



1 162. To preserve dung for any time, the situation in which it is kept is of importance. 

 It should, if possible, be defended from the sun. To preserve it under sheds would be 

 of great use ; or to make the site of a dunghill on the north side of a wall. The floor 

 on which the dung is heaped, should, if possible, be paved with flat stones ; and there 

 should be a little inclination from each side towards the centre, in which there should be 

 drains connected with a small well, furnished with a pump, by which any fluid matter 

 may be collected for the use of the land. It too often happens that a dense mucilaginous 

 and extractive fluid is suffered to drain away from the dunghill, so as to be entirely lost 

 to the farm. 



SECT. II. Of Manures of Mineral Origin. 



1 163. Earthy and saline manures are probably of more recent invention, and doubtless 

 of more uncertain use than those of animal and vegetable origin. The conversion of 

 matter that has belonged to living structures into organised forms, is a process that can 

 be easily understood ; but it is more difficult to follow those operations by which earthy 

 and saline matters are consolidated in the fibre of plants, and by which they are made 

 subservient to their functions. These are capable of being materially elucidated by 

 modern chemistry, and shall here be considered as to the theory of their operation, and 

 specific kinds. 



SUBSECT. 1. Theory of the Operation of Mineral Manures. 



1164. Saline and calcareous substances form the principal fossil manures. Much has 

 been written on lime and common salt, both in the way of speculation and reasoning 

 from facts, which, from want of chemical knowledge, has turned to no useful account, and 

 cultivators till very lately contented themselves with stating that these substances acted as 

 stimuli to the soil, something like condiments to the digestive organs of animals. Even 

 chemists themselves are not yet unanimous in all their opinions; but still the result of 

 their enquiries will be found of great benefit to the scientific cultivator. 



1165. Various opinions exist as to the rationale of the operation of mineral manures. 

 " Some enquirers," Sir H. Davy observes, " adopting that sublime generalisation of 

 the ancient philosophers, that matter is the same in essence, and that the different sub- 

 stances, considered as elements by chemists, are merely different arrangements of the 

 same indestructible particles, have endeavoured to prove, that all the varieties of the prin- 

 ciples found in plants, may be formed from the substances in the atmosphere ; and that 

 vegetable life is a process in which bodies that the analytical philosopher is unable to 

 change or to form, are constantly composed and decomposed. But the general results 

 of experiments are very much opposed to the idea of the composition of the earths, by 

 plants, from any of the elements found in the atmosphere, or in water ; and there are 

 various facts contradictory to the idea. Jacquin states, that the ashes of glass-wort (Sal-, 



R 2 



