EXPERIMENTS OF BOUSSINGAULT. 199 



tained in crops of potatoes and turnips scarcely corresponds to 

 more than the quantity in crops of wheat, it follows that they 

 could not have the power to form their azotized constituents with- 

 out manure ; so that nothing remains, except to ascribe to the 

 clover the excess of nitrogen obtained. This explains, also, why 

 the excess is so much greater in the third rotation than in any of 

 the preceding ; for it will be remarked, that in the third rotation 

 a sixth crop was introduced, corresponding to the same family as 

 clover. If, therefore, there had been neither peas nor clover in 

 the third rotation, but, instead of these plants, one of another 

 family, the nitrogen of the crop would have amounted only to the 

 quantity supplied in the manure. Boussingault concludes that 

 leguminous plants alone possess the power of appropriating, as 

 food, nitrogen from the air, and that other cultivated plants do not 

 at all possess this property. Hence the great importance which 

 Boussingault ascribes to manures containing nitrogen, for, ac- 

 cording to his view, the commercial value of a manure depends 

 on its amount of nitrogen. But all these conclusions are tho- 

 roughly erroneous; for, if they were not so, it must follow that 

 potash, lime, and silica plants, unless they belonged to the Legu- 

 minosse, would not produce any nitrogen, unless they were sup- 

 plied with manure containing that element. 



The conclusions of Boussingault are not only erroneous in their 

 applications to agriculture, but are incorrect in the methods 

 which he employs ; for the manure was not given to the fields in 

 the form in which he analysed it. 



Let us assume that the manure which he put upon his fields 

 possessed the same state in which it was analysed (dried at 

 230° F. in vacuo) ; then the field would receive in the sixteen 

 years 1300 lbs. of nitrogen. But the manure was not put upon 

 the field in an anhydrous state, but, on the contrary, in its natu- 

 ral moist condition, soaked with water ; and we know that all the 

 nitrogen contained in the manure in the form of carbonate of am- 

 monia is volatilized when it is dried at a high temperature. The 

 nitrogen of the urine in the manure, which is converted by putre- 

 faction into carbonate of ammonia, is not included in the 1300 lbs. 

 of the above calculation. 



Human excrements, dried in the air at ordinary temperature 



