1 06 LESSONS IN CHEMISTRT. 



structure, and the loss of which, by the sale of our farm 

 produce, must as eiFectually impoverish our fields, as if we 

 were, by a chemical process, to remove from them these 

 ingredients. Crops of weeds spring up in neglected places, 

 year after year, without any decrease in luxuriance, because 

 they die on the spot where they have been produced, and 

 restore, by their decay, the matters on which they had lived, 

 and thus keep up the fertility of the soil ; but it is not possi- 

 ble, in this manner, to maintain the productiveness of our 

 cultivated fields. Only that part of the plant produced which 

 is unfit for food, can be directly restored. But, although we 

 cannot directly replace in the soil the seeds, the roots, and 

 the fibre employed for food and clothing, Nature has so 

 arranged, that all the materials which during their growth, 

 they have abstracted from it, after they have fulfilled the 

 important purposes for which they are cultivated, may, by 

 the care of the husbandman, be collected and restored, for 

 the production of new crops of vegetables. In the present 

 arrangements of these countries, however, but little attention 

 is devoted to these sources of manm-e ; and farmers are every 

 year obUged to expend large sums of money, in the purchase 

 of substances to replace the materials of their soils, washed 

 into the sewers and rivers of the country. 



151. You have seen, that the power of the soil to yield 

 crops, depends upon its containing a full supply of certain 

 mineral matters, which serve for their nourishment. From 

 the most remote periods, farmers have been accustomed to 

 apply to their exhausted fields the excrements of animals and 

 of birds, and have found that these manures were capable of 

 renewing their fertility. It is only of late years, however, 

 that the cause of the valuable properties of these matters has 

 been satisfactorily investigated, nor is the explanation difficult 

 to understand. The food consumed by man and animals 

 becomes a part of their bodies. — The roots and grasses which 

 the cow eats contain the mmeral matters which gave fertility 

 to the fields in which they were grown, so that these matters 

 become a portion of the bone and flesh of the animal. The 

 seeds, roots, and flesh which afford us food must, in the same 

 manner, enter into our substance ; and when the flesh of an 

 animal is dried and burned, it is found, like the vegetable, to 

 consist of two portions, one of which, sunilar to the organic 

 part of the plant, is combustible and disappears (41), and a 



