34 The Advantages of Chemical Science. 



furious to crops, but by simple chemical tcs'.s the nature of a 

 lime-stone is discovered in a few minutes, and the fitness of 

 its application, whether as a manure for .different soils or a 

 cement, determined. There has been no question on which 

 more difference of opinion has existed than that, of the state in 

 ■which manure ought to be ploughed into the land, whether re- 

 cent or when it has gone through the process of fermentation ; 

 and thit, question is still a subject of discussion ; but whoever 

 will refer to the simples and principles of chemistry cannot 

 entertain a doubt on the subject, — as soon as dung begins to 

 decompose it throws off its volatile parts, which are the most 

 valuable and most efficient. Dung which has fermented, so as 

 to become a mere soft cohesive mass, has generally lost from 

 one-third to one-half of its most useful constituent elements; 

 and that it may exert its full action upon the plant and lose 

 none of its nutritive powers, it should evidently be applied 

 much sooner, and long before decomposition has arrived at its; 

 ultimate results. 



The phenomena of vegetation must be considered as an im- 

 portant branch of the science of organised nature, but though 

 exalted above inorganic matter, vegetables are yet, in a great 

 measure, dependent for their existence upon its laws; they re- 

 ceive their nourishment from the external elements, they as- 

 similate it by means of peculiar organs, and it is by examining 

 their physical and chemical constitution, and the substances and 

 powers which act upon them, and the modifications which they 

 undergo, that the scientific principles of agricultural chemistry 

 are obtained; according to these ideas, therefore, the surface 

 of the earth, the atmosphere, and the water deposited from it, 

 must, either together or separately, afford all the principles 

 concerned in vegetation, and it is only by examining' the 

 chemical nature of these principles that we are capable of dis- 

 covering what is the food of plants, and the manner in which 

 this food is supplied and prepared for their nourishment. 



The chemical composition of plants has, within the last ten 

 years, been elucidated by the experiments of a number of 

 chemical philosophers, and it forms a beautiful part of general 

 chemistry ; it is too extensive to be treated of minutely, but it 

 will be necessary to dwell upon such parts of it as afford prac- 

 tical inferences. The value ai:d uses of every species of agri- 

 cultural produce are most correctly estimated and applied, 

 when practical knowledge is assisted by principles derived 

 from chemistry, the compounds in vegetables really nutritive, 

 as the food of animals are very (aw, — farina or the pure mat- 

 ter of statch, gluten, sugar, vegetable jelly, oil and extract; 

 of these, the most outjUivcis gluten, which approaches nearest 



