AGRICULTURAL CIIEMISTRY. 185 



manmivrcr, {main ouvrer,) or Latin manus operor, signifying to work 

 with the hands, a sense in which it was employed by Milton. The 

 term manure is now used in a general way to signify any substance 

 added to the soil to make it more productive. 



Substances added in large quantity often act chiefly by qualifying 

 the physical properties of the soil, and are then appropriately termed 

 Amendments. Matters which operate in the main by feeding vegeta- 

 tion are more properly Fertilizers. These again may nourish directly, 

 by supplying at once to the growing plant one or all the nutrient in- 

 gredients it requires; or indirectly, by making soluble the stores of 

 the soil, or otherwise disposing them to assume assimilable forms, or 

 by absorbing matters from the atmosphere. Most manures combine 

 these various offices to a greater or less degree. 



While the popular name of those materials that are successfully 

 employed as manures is legion, the chemist, by his analysis, recog- 

 nizes in them all only the same dozen kinds of matter which consti- 

 tute plants and soils. 



The use of manures has been known from the earliest times, and 

 there has been no lack of attempts to explain their effects; but it is 

 only after the sciences of chemistry and vegetable physiology had 

 entered upon the modern development that it was possible to begin 

 understanding their mode of action. So difficult is the subject that 

 we are as yet by no means advanced to its full comprehension, which 

 requires a complete knowledge of the relations of each nutritive 

 element and compound with the plant, with the soil, and with the 

 atmosphere. 



During all the centuries in which agricultural experience, with 

 reference to the operation of manures, has accumulated, we find that 

 the opinions of practical farmers have been almost endlessly at 

 variance; and as these conflicting opinions have faithfully reflected 

 the facts and phenomena which have presented themselves to agri- 

 culturists, we are prepared to find that at the present day there is 

 a constant recurrence of endlessly differing results in the use and 

 estimate of manures. We find in our current agricultural journals 

 abundant examples of crops being benefited by application of nearly 

 every one of the ash ingredients of the plant, as well as by ammonia 

 and nitrates, or bodies yielding these; and, on the other hand, re- 

 peated instances of their failure. A scientific consideration of these 

 results enables us to explain much that is obscure, and reconcile 

 much that is conflicting, by taking into the account differences of soil, 

 climate, and crop; and by a careful study of the circumstances which 

 alter cases to such a great degree, it will be possible, in time, to 

 unfold every mystery and elucidate every variety of effect. 



The space at command here docs not allow any detail with refer- 

 ence to the action of manures, except as may illustrate some of the 

 general principles which alone can serve to initiate us into the 

 method of their operation. 



