INTEODUCTION. 21 



quainted with. The gist of agricultural chemistry with 

 him was, that plants are " composed of gases with a small 

 proportion of calcareous matter ; " for " although this 

 discovery may appear to be of small moment to the prac- 

 tical farmer, yet it is well deserving of his attention and 

 notice, as it throws great light on the nature and food of 

 vegetables." The fact being then known that plants ab- 

 sorb carbonic acid from the air, and employ its carbon in 

 their growth, the theory was held that fertilizers operate 

 by promoting the conversion of the organic matter of the 

 soil or of composts into gases, or into soluble humus, 

 which were considered to be the food of plants. 



The first accurate analysis of a vegetable substance was 

 not accomplished until 15 years after the publication of 

 Dundonald's Treatise, and another like period passed be- 

 fore the means of rapidly multiplying good analyses had 

 been worked out by Liebig. So late as 1838, the Gottingen 

 Academy offered a prize for a satisfactory solution of the 

 then vexed question whether the ingredients of ashes are 

 essential to vegetable growth. It is, in fact, during the last 

 30 years that agricultural chemistry has come to rest on 

 sure foundations. Our knowledge of the structure and 

 physiology of plants is of like recent development. 

 What immense practical benefit the farmer has gathered 

 from this advance of science ! The dense populations of 

 Great Britain, Belgium, Holland, and Saxony, can attest 

 the fact. Chemistry has ascertained what vegetation ab- 

 solutely demands for its growth, and points out a multitude 

 of sources whence the requisite materials for crops can be 

 derived. To be sure, Cato and Columella knew that ashes, 

 bones, bird-dung and green manuring, as well as drain- 

 age and aeration of the soil, were good for crops ; but 

 that carbonic acid, potash, phosphate of lime, and com- 

 pounds of nitrogen, are the chief pabulum of vegetation, 

 they did not know. They did not know that the atmos--' 

 phere dissolves the rocks, and converts inert stone into 



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