ON THE NITROGEN OF PLANTS. 
231 
same property in an eminent degree. It possesses proper- 
ties 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 cer- 
tain other substances, it completely resigns its character as 
an alkali; and is capable of assuming the most various and 
opposite forms. Formate of ammonia changes, under the in- 
fluence of a high temperature, into hydrocyanic acid and 
water, without the separation of any of its elements. Ammo- 
nia forms urea with cyanic acid, and a series, of crystalline 
compounds, with the volatile oils of mustard and bitter al- 
monds. It changes into splendid blue or red coloring matters 
when in contact with the bitter constituent of the bark of the 
apple-tree (phloridzin,) with the sweet principle of the 
Variolaria dealbata (orcinj or with the tasteless matter [of 
the Rocella tinctoria ( erythrin. ) All blue coloring matters 
which are rendered red by acids, and all red coloring substances 
which are 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 nitrogen which enters into the composition of their con- 
stituent substances. Considerations of another kind, how- 
ever, give to this opinion a degree of certainty, which com- 
pletely 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 pro- 
duces, 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 importa- 
tion of any foreign substance containing nitrogen. Now, the 
products of this farm must be exchanged every year for 
money, and other necessaries of life, for bodies, therefore, 
which contain no nitrogen. A certain 'proportion of nitrogen 
is exported with corn and cattle ; and this exportation takes 
