CHEMICAL MANURES. 51 



exhausted, there would always remain the azote of the air, which is 

 thrown off by the plants themselves. 



But this is an extreme supposition. When humanity rests upon a 

 problem, be assured, gentlemen, at the proper moment the problem 

 will be solved. 



The air being an inexhaustible source of azote, what remains for 

 us to do to have the nitrate and ammonia in illimitable quantities is to 

 discover the most economical method of combining the azote of the 

 air with oxygen to form nitrates, or with hydrogen to form ammonia. 

 Now this process is discovered, Messrs. Sourdeval and Margueritte 

 having found the means of making the nitrate or ammonia at will 

 with the azote of the air. If the working of it is limited, it is only 

 that, in an economical point, it does not satisfy all the conditions of 

 an easy production. But the principle is known, and the solution 

 may at any moment be complete. 



I ask, gentlemen, if, in the face of such facts, azotic matter will 

 ever be wanting ? As to lime, I do not speak of it, for we all know 

 there never will be a deficiency of it. 



Assured for the future, let us recapitulate the matter of the past 

 lecture. 



In our preceding sittings we have been employed in defining, by 

 the aid of experiments more scientific than practical, the conditions 

 which regulate the production of plants. 



To-day, entering the domain of the practical, we have asked from 

 the traditions of centuries of experience that is, from the composi- 

 tion of dung the choice of agents which, in our eyes, are the sym- 

 bols of fertility. This test has ended in our favor. Dung contains 

 these agencies, and owes its fertility to them. 



To this testimony we have added another. We asked of practical 

 agriculture, If the effects obtained from the chemical fertilizers were 

 not equivalent to those obtained from manure ? Experience replies, 

 They \vere superior. From which we conclude that the principles 

 we hold are incontestable, and there remains for us but to generalize 

 their application. 



