22 CHEMICAL MANURES. 



absorbed? Is it in the ammoniac, nitrate or elementary form of 

 azote ? 



Before pronouncing with certainty with regard to this, we have a 

 question difficult of solution. We must know if the air contains the 

 ammoniac and nitrate forms, and if so, in what proportions. 



There is no doubt on these two points. The air contains both the 

 ammoniac and nitrate forms, but so feeble, so weakened, that they 

 belong to the infinitely small. 



The proportion of ammonia is comprised between 

 0.000,000,017 and 

 0.000,000,032. 



This corresponds to nearly one half ounce of ammoniac for 

 2,000,000 pounds of air. A thimble by the side of the Pantheon ! 

 The air, as we have said, contains nitric acid in infinitely reduced 

 proportions, hardly equal to that of ammoniac. In the face of such 

 small quantities it is not possible to attribute to them the enormous 

 mass of azote that plants draw from the air. To escape this diffi- 

 culty, the nitrates and salts of ammonia being very soluble in water, 

 we admit it is the office of the rain to condense them and bring them 

 in a feeble volume to the plants. But this supposition cannot sustain 

 itself when we examine tilings a little nearer. 



Rain water contains at least 0.0005 ammoniac and the same quan- 

 tity of nitre to the 2 T ^ pints. Now these quantities correspond to a 

 deposit of 2.66 pounds of azote the acre per year, which is evidently 

 insufficient to explain the excess of 38.03 pounds shown by the sweet 

 potato, and still more so for that of lucerne, which reaches 151 

 pounds. Neither the ammoniac nor the nitrates of the air can 

 account for the excess of azote which harvests yield. 



We are then led to attribute to the elementary azote of the air an 

 excess which would otherwise be inexplicable. , 



Is this view admitted without dispute? No; and these are the 

 objections raised to it. 



It is unanimously agreed that a part of the azote of a crop is 

 drawn from the air, but the assimilation of elementary azote is denied. 

 It is supposed that, before being absorbed by the plant, azote passes 

 into the soil as a nitrate. The soil then becomes the seat of a uni- 

 versal and permanent nitrification. 



Thus announced, this opinion does not bear an instant's examina- 

 tion. If azote enters lucerne but in the form of a nitrate, is it not 

 evident that in a crop of it we ought to find the corresponding basis 

 to nitric acid, the supposed source of azote ? Now, there is none to 

 be found. Now, in a crop of lucerne gotten here and on the farm of 

 Vincennes, azote surpassed its corresponding basis by 120 pounds the 

 acre ; 120 pounds have therefore not entered the plant in the form 

 of a nitrate. This 120 pounds is but one-third the real quantity of 

 azote the acre that lucerne draws from the air, seeing that in the 

 example just cited azote in the form of nitrate of potash and nitrate 

 of soda were intentionally introduced in the fertilizers ; and it has 

 been shown me since that equally large returns may be obtained by 



