76 CHYMISTRY APPLIED TO AGRICULTURE. 



in water, are carried more abundantly into plants, pro- 

 ducing upon them the most injurious effects. 



The greater part of those salts which are found in 

 plants serve no purpose of nourishment ; they are gene- 

 rally useful only as stimulating the organs and aiding di- 

 gestion. Animals, as they enjoy the power of locomotion, 

 can easily procure for themselves these stimulants and 

 whatever is needful for the exercise of their offices, and 

 they take only such quantities and in such proportions as 

 are suitable for them. But plants -have no other medium 

 than air and water, through which to receive their sup- 

 plies; and this last transmits to them indiscriminately all 

 which it can dissolve from the soil ; whence it follows, 

 that the best saline manures are those that can be only 

 gradually dissolved. 



This principle is applicable to all manures of whatever 

 nature. There is, however, this difference in the effects of 

 manures purely nutritive, and of the stimulating or saline 

 manures; if the first be too abundant, the plant absorbs 

 more nourishment than it can readily digest, and becomes 

 affected by a kind of obesity ; the texture of its organs is 

 rendered soft, loose, and spongy, and unable to give to 

 their products the due degree of consistency ; whilst, on 

 the contrary, if the stimulating manures be supplied too 

 profusely, and especially if they be of kinds very soluble 

 in water, the organs of the plants are dried and parched 

 by the excess which they receive. 



Those animal substances that are the most slowly de- 

 composed, and which by their decomposition always give 

 rise to soluble products, are the best of all manures : of 

 this bones, horns, and wool, afford a sufficient proof 

 These substances possess the advantage of affording to 

 plants their suitable aliments, almost always combined 

 with a stimulant, such as ammonia, of which the too irri- 

 tating action is moderated by its union with carbonic 

 acid or with animal matter. 



The ashes of turf and of pit coal produce wonderful 

 effects upon grass lands. The first of these often con- 

 tains gypsum, but frequently only silica, alumina, and 

 oxide of iron. From ashes of pit coal I have obtained 

 by analysis sulphuret of lime. 



The ashes, produced by the combustion of wood in our 

 common domestic fires„ give rise to some very remarkable 

 results. Without being leached these ashes are much too 



