106 CHYMISTRY APPLIED TO AGRICULTURE. 



as is suitable for them; but in both cases the nutritive 

 virtues of the food can be estimated only by the results 

 of its elaboration in the digestive organs, and by the 

 effects produced on the economy of the animal or vegeta- 

 ble. It should besides be remembered, that the nutritive 

 qualities of the various products of vegetation depend 

 less upon their weight, than their kind; and that a sub- 

 stance may be insoluble in water, which may, when acted 

 upon by the gastric juices, become excellent food. 



CHAPTER VI. 



IMPROVEMENT OF THE SOIL. 



To improve the soil is to render it more suited to vege- 

 tation by ameliorating the nature of the earth. All then 

 which tends to dispose a soil favorably towards plants, in 

 connection with the action which is exercised upon them 

 by air, water, temperature, manures, &c., may be justly 

 termed improvement. Thus, before undertaking to im- 

 prove a soil, it is necessary to be acquainted with its 

 qualities, and particularly with its defects, that we may 

 apply to it the means of improvement it requires. 



This preliminary knowledge of the defects of a soil 

 implies a second, which is that of all the agents which 

 can be employed in its improvement : the correction of 

 known feults can only be performed by means of sub- 

 stances possessing opposite qualities. 



As in the term improvement is implied all which can 

 tend to ameliorate a soil, it necessarily has a very exten- 

 sive signification ; it comprehends operations purely me- 

 chanical, and the use of those earthy and nutritive mix- 

 tures, which are produced by art; it likewise comprises 

 all the means which can be employed to direct advanta- 

 geously the action of air, water, heat, &.c. It is in all 

 these relations, that it is necessary to consider the great art 

 of improvement. 



The best earths produce but little, if they be not stirred 

 by the spade, the hoe, or the plough. This operation 

 divides and soflens the earth, brings to the surface the 

 manures of all kinds, which the rains had caused to sink 



