SOURCE AND ASSIMILATION OF NITROGEN. 41 



of this element conveyed to their roots in the state of ammonia, 

 derived from the putrefaction of animal matter. 



Ammonia, too, is capable of undergoing such a multitude of 

 transformations, when in contact with other bodies, that in this 

 respect it is not inferior to water, which possesses the same pro- 

 perty in an eminent degree. It possesses properties which we 

 do not find in any other compound of nitrogen ; when pure, it is 

 extremely soluble in water ; it forms soluble compounds with all 

 the acids ; and when in contact with certain other substances, it 

 completely resigns its character as an alkali, and is capable of 

 assuming the most various and opposite forms. Formate of am- 

 monia changes, under the influence of a high temperature, into 

 hydrocyanic acid and water, without the separation of any of its 

 elements. Ammonia forms urea, with cyanic acid, and a series 

 of crystalline compounds, with the volatile oils of mustard and 

 bitter almonds. It changes into splendid blue or red coloring 

 matters, when in contact with phloridzin, the bitter constituent of 

 the bark of the root of the apple-tree, with orcin, the sweet prin- 

 ciple of the Lichen dealbatus, or with erythrin, the tasteless matter 

 of the Rocella tinctoria. All blue coloring matters capable of 

 being reddened by acids, and all red coloring substances rendered 

 blue by alkalies, contain nitrogen, but not in the form of a base. 



These facts are not sufficient to establish the opinion that it is 

 ammonia which affords all vegetables, without exception, the ni- 

 trogen of their constituent substances. Considerations of another 

 kind, however, give to this opinion a degree of certainty which 

 completely excludes all other views of the matter. 



Let us picture to ourselves the condition of a well-cultured 

 farm so large as to be independent of assistance from other 

 quarters. On this extent of land there is a certain quantity of 

 nitrogen contained both in the corn and fruit which it produces, 

 and in the men and animals which feed upon them, and also in their 

 excrements. We shall suppose this quantity to be known. The 

 land is cultivated without the importation of any foreign sub- 

 stance containing nitrogen. Now, the products of this farm 

 must be exchanged every year for money, and other necessaries 

 of life — for bodies, therefore, destitute of nitrogen. A certain 

 proportion of nitrogen is exported in the shape of corn and cat- 



