52 SOURCE AND ASSIMILATION OF NITROGEN. 



All putrefying animal matters emit carbonic acid and ammonia 

 as long as nitrogen exists in them. In every stage of their putre- 

 faction an escape of ammonia from them may be induced by- 

 moistening them with a potash ley ; the ammonia being apparent 

 to the senses by a peculiar smell, and by the dense white vapor 

 exhibited when a solid body moistened with an acid is brought 

 near it. This ammonia evolved from manure is imbibed by the 

 soil either in solution in water, or in 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 ammonia yielded to a soil 

 by animal excrements, 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 wateF 

 evaporated through their leaves and blossoms emits, after some 

 time, a putrid smell, a peculiarity possessed only by bodies con- 

 taining nitrogen. Cultivated plants receive the same quantity of 

 nitrogen from the atmosphere as trees, shrubs, and other wild 



* " I filled a large retort," says Sir H. Davy, " capable of containing 

 three pints of water, with some hot fermenting manure, consisting prin- 

 cipally of the litter and dung of cattle ; and adapted a small receiver to 

 the retort, and connected the whole with a mercurial pneumatic appa- 

 ratus, so as to collect the condensible and elastic fluids which might rise 

 from tb*> dung. The receiver soon became lined with dew, and drops 

 began in a few hours to trickle down the sides of it. Elastic fluid like- 

 wise was generated ; in three days 35 cubical inches had been formed, 

 which, when analysed, were found to contain 21 cubical inches of car- 

 bonic acid ; the remainder was hydro-carbonate mixed with some azote, 

 probably no more than existed in the common air in the receiver. The 

 fluid matter collected in the receiver at the same time amounted to 

 nearly half an ounce. It had a saline taste, and a disagreeable smell, 



nd contained some acetate and carbonate of ammonia. 

 " Finding such products given off from fermenting litter, I introduced 



he beak of another retort, filled with similar dung very hot at the 

 Vime, into the soil amongst the roots of some grass in the border of a 

 garden ; in less than a week a very distinct effect was produced on the 

 grass ; upon the spot exposed to the influence of the matter disengaged 

 in fermentation, it grew with more luxuriance than the grass in any 

 other part of the garden." — Works of Sir H. Davy, Edited by Dr. Johc 

 Davy, vol. viii., page 31 



