so 



AGRICULTURAL CHEMISTRY. 



The numerous springs which emit car- 

 bonic acid in the neighbourhood of extinct 

 volcanoes, must be regarded as another 

 means of compensating for the carbonic acid 

 absorbed and retained by plants during life, 

 and consequently as a source by which oxy- 

 gen is supplied to the atmosphere. Bischof 

 calculated that the springs of carbonic acid 

 in the Eifel (a volcanic district near Cob- 

 lenz) send into the air every day more than 

 1 10,000 Ibs. of carbonic acid, corresponding 

 to 79,000 Ibs. of pure oxygen. 



. CHAPTER V. 



ON THE ORIGIN AND ASSIMILATION OF 

 NITROGEN. 



WE cannot suppose that a plant could 

 attain maturity, even in the richest vege- 

 table mould, without the presence of matter 

 containing nitrogen; since we know that 

 nitrogen exists in every part of the vegetable 

 structure. The first and most important 

 question to be solved, therefore, is: How 

 and in what form does nature furnish nitro- 

 gen to vegetable albumen, and gluten, to 

 fruits and seeds? 



This question is susceptible of a very 

 simple solution. 



Plants, as we know, grow perfectly well 

 in pure charcoal, if supplied at the same 

 time with rain water. Rain water can con- 

 tain nitrogen only in two forms, either as 

 dissolved atmospheric air, or as ammonia, 

 which consists of this element and hydro- 

 gen. Now, the nitrogen of the air cannot 

 be made to enter into combination with any 

 element except oxygen, even by the employ- 

 ment of the most powerful chemical means. 

 We have not the slightest reason for believ- 

 ing that the nitrogen of the atmosphere 

 takes part in the processes of assimilation 

 of plants and animals; on the contrary, we 

 know that many plants emit the nitrogen 

 which is absorbed by their roots, either in 

 the gaseous form, or in solution in water. 

 But there are on the other hand numerous 

 facts, showing, that the formation in plants 

 of substances containing nitrogen, such as 

 gluten, takes place in proportion to the 

 quantity of this element which is conveyed 

 to their roots in the state of ammonia, de- 

 rived 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 pos- 

 sesses the same property in an eminent de- 

 gree. 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 

 characters an a.kali, and is capable of as- 



suming the most various and opposite forms 

 Formate of ammonia changes, under the 

 influence of a high temperature, into hy- 

 drocyanic acid and water, without the sepa- 

 ration of any of its elements. Ammonia forms 

 urea, with cyanic acid, and a series of crys- 

 talline compounds, with the \olatile oils of 

 mustard and bitter almonds. It changes 

 into splendid blue or red colouring matters, 

 when in contact with the bitter constituent 

 of the bark of the apple-tree (phloridzin,) 

 with the sweet principle of the F^ariolaiia 

 dealbata (orcm,) or with the tasteless matter 

 of the Rocella tinctoria (en///inn.) All blue 

 colouring matters which are reddened by 

 acids, and all red colouring 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 nitro- 

 gen which enters into the composition of 

 their constituent substances. Considerations 

 of another kind, however, give to this opi- 

 nion 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 in- 

 dependent 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 substance containing nitro- 

 gen. Now, the products of this farm 'must 

 be exchanged every year for money, and 

 other necessaries of life for bodies, there- 

 fore, which contain no nitrogen. A certain 

 proportion of nitrogen is exported with corn 

 and cattle ; and this exportation lakes place 

 every year, without the smallest compensa- 

 tion ; yet after a given number of years, the 

 quantity of nitrogen will be found to have 

 increased. Whence, we may ask, comes 

 this increase of nitrogen? The nitrogen in 

 the excrements cannot reproduce itself, and 

 the earth cannot yield it. Plants, and con- 

 sequently animals, must, therefore, derive 

 their nitrogen from the atmosphere. 



It will in a subsequent part of this work 

 be shown that the last products of the decay 

 and putrefaction of animal bodies present 

 themselves in two different forms. They 

 are in the form of a combination of hydro- 

 gen and nitrogen ammonia in the temper- 

 ate and cold climates, and in that of a com- 

 pound containing oxygen nitric acid in 

 the tropics and hot climates. The forma- 

 tion of the latter is preceded by the produc- 

 tion of the first. Ammonia is the last pro- 

 duct of the putrefaction of animal bodies; 

 nitric acid is the product of the transforma- 

 tion of ammonia. A generation of a thou- 

 sand million men is renewed every thirty 

 years : thousands of millions of animafs 

 cease to live and are reproduced, in a much 



