34 



AGRICULTURAL CHEMISTRY. 



alive by feeding it with potatoes, which con- 

 tain a very small quantity of nitrogen ; but 

 life thus supported is a gradual starvation; 

 the animal increases neither in size nor 

 strength, and sinks under every exertion. 

 The quantity of rice which an Indian eats 

 astonishes the European ; but the fact that 

 rice contains less nitrogen than any other 

 kind of grain at once explains the circum- 

 stance. 



Now, as it is evident that the nitrogen of 

 the plants and seeds used by animals as food 

 must be employed in the process of assimila- 

 tion, it is natural to expect that the excre- 

 ments of these animals will be deprived of it 

 in proportion to the perfect digestion of the 

 food, and can only contain it when mixed 

 with secretions from the liver and intestines. 

 Under all circumstances, they must contain 

 less nitrogen than the food. When, there- 

 fore, a field is manured with animal excre- 

 ments, a smaller quantity of matter contain- 

 ing nitrogen is added to it than has been 

 taken from it in the form of grass, herbs, or 

 seeds. By means of manure, an addition 

 only is made to the nourishment which the 

 air supplies. 



In a scientific point of view, it should be 

 the care of the agriculturist so to employ all | 

 the substances containing a large proportion 

 of nitrogen which his farm affords in the 

 form of animal excrements, that they shall 

 serve as nutriment to his own plants. This 

 will not be the case unless those substances i 

 are properly distributed upon his land. A 

 heap of manure lying unemployed upon 

 his land would serve him no more than his 

 neighbours. The nitrogen in it would es- | 

 cape as carbonate of ammonia into the at- 

 mosphere, and a mere carbonaceous residue 

 of decayed plants would, after some years, 

 be found in its place. 



All animal excrements emit carbonic acid 

 and ammonia, as long as nitrogen exists in 

 them. In every stage of their putrefaction 

 an escape of ammonia from them may be 

 induced by moistening them with a potash 

 ley ; the ammonia being apparent to the j 

 senses by a peculiar smell, and by the dense j 

 white vapour which arises when a solid 

 body moistened with an acid is brought near 

 it. This ammonia evolved from manure is 

 imbibed by the sojl either in solution in ! 

 water, or m the gaseous form, and plants 

 thus receive a larger supply of nitrogen 

 than is afforded to them by the atmosphere. 



But it is much less the quantity of am- 

 monia, yielded to a soil by animal excre- 

 ments, than the form in which it is presented 

 by them, that causes their great influence 

 on its fertility. Wild plants obtain more 

 nitrogen from the atmosphere in the form of 

 ammonia than they require for their growth, 

 for the water which evaporates through their 

 leaves and blossoms, emits, after some time, 

 a putrid smell, a peculiarity possessed only 

 by such bodies as contain nitrogen. Culti- 

 vated plants receive the same quantity of 

 nitrogen from the a'.mospnsre as trees, 



shrubs, and other wild plants; but this is 

 not sufficient for the purposes of agricul- 

 ture. Agriculture differs essentially from 

 the cultivation of forests, inasmuch as its 

 principal object consi ts in the production 

 of nitrogen under any form capable of as- 

 similation ', whilst the object of forest culture 

 is confined principally to the production of 

 carbon. All the various means of culture 

 are subservient to these two main purposes. 

 A part only of the carbonate of ammonia 

 which is conveyed by rain to the soil is re- 

 ceived by plants, because a certain quantity 

 of it is volatilised with the vapour of water : 

 only that portion of it can be assimilated 

 which sinks deeply into the soil,, or wlucn 

 is conveyed directly to the leaves by dew, or 

 is absorbed from the air along with the car- 

 bonic acid. 



Liquid animal excrements, such as the 

 urine with which the solid excrements are 

 impregnated, contain the greatest part ot 

 their ammonia in the state of salts, in a form, 

 therefore, in which it has completely lost its 

 volatility ; when presented in this condition, 

 not the smallest portion of the ammonia is 

 lost to the plants; it is all dissolved by water, 

 and imbibed by their roots. The evident 

 influence of gypsum upon the growth of 

 grasses the striking fertility and luxuriance 

 of a meadow upon which it is strewed 

 depends only upon its fixing in the soil the 

 ammonia of the atmosphere, which would 

 otherwise be volatilized, with the water 

 which evaporates.* The carbonate of am- 

 monia contained in rain-water is decom- 

 posed by gypsum, in precisely the same 

 manner as in the manufacture of sal-am- 

 moniac. Soluble sulphate of ammonia and 

 carbonate of lime are formed ; and this salt 

 of ammonia possessing no volatility is con- 

 sequently retained in the soil. All the gyp- 

 sum gradually disappears, but its action 

 upon the carbonate of ammonia continues 

 as long as a trace of it exists. 



The beneficial influence of gypsum and of 

 many other salts has been compared to that 

 of aromatics, which increase the activity of 

 the human stomach and intestines, and give 

 a tone to the whole system. But plants con- 

 tain no nerves ; we know of no substance 

 capable of exciting them to intoxication and 

 madness, or of lulling them to sleep and re- 

 pose. No substance can possibly cause their 

 leaves to appropriate a greater quantity of 

 carbon from the atmosphere, when the other 

 constituents which the seeds, roots, and 

 leaves require for their growth are wanting. 

 The favourable action of small quantities of 

 aromatics upon man, when mixed with his 

 food, is undeniable ; but aromatics are given 

 to plants without food to be digsted, and 

 still they flourish with greater luxuriance. 



* It has long been the practice in some parts of 

 the country to strew the floors of stables with 

 gypsum. This prevents the disagreeable odour 

 arising from the putrefaction of stable manure, by 

 decomposing the ammouiacai saks which are 

 formed. ED. 



