GAS FROM LEAVES CONTAINS NITROGEN. 



this, I exposed a quantity of boiled water, which had been suffered to cool in vacuo, 

 to carbonic acid gas, of which it absorbed a certain amount. A portion of this water 

 was placed in the focus of the brass mirror, and was there acted upon by the non-lumi- 

 nous rays ; its temperature never exceeded 140 Fah. In a short time the pine leaves 

 commenced giving off gas very copiously, and continued to do so ; but it was found, 

 on trial, that nearly the whole of it was absorbed by lime-water, and that no decom- 

 position had occurred. Therefore, though rays of non-luminous heat are competent to 

 cause the evolving of gas, they are not able to cause decomposition. 



425. The record of an analysis will place this effect in its true light : care being 

 taken that the water should be impregnated with pure carbonic acid gas, and the leaves 

 recent, when a sufficient quantity was evolved, 39 measures were taken, of which caustic 

 potassa absorbed 34. Hydrogen gas being then added, a diminution to the amount of 4 

 volumes was produced by a platinum ball; the remaining gas proved to be nitrogen. 

 The composition of this gas was, therefore, 



Carbonic acid 34-00 



Nitrogen 3-67 



Oxygen 1-33 



39-00 



It is proper to observe that a change very evidently takes place in the structure of the 

 vegetable leaves, their colour becoming of a dirty brown, and their greenness is lost. 

 Whether it is a change of their acting tissue which hinders decomposition, or whether 

 there is some peculiarity in the constitution of non-luminous heat, which incapacitates 

 it from producing those effects which result from caloric radiating from highly incan- 

 descent bodies, I shall proceed to discuss. 



426. Let us first consider what is the action of an ordinary unchanged sunbeam on car- 

 bonic acid in solution, and in contact with vegetable matter. A wide distinction is 

 here to be made between common spring water, such as pump water, and water charged 

 with carbonic acid only ; the former contains a compound of oxygen and nitrogen, 

 isomeric with protoxide of nitrogen ; but the protoxide is a chemical compound, having 

 its two volumes of nitrogen compressed into one, while this is a capillary compound, 

 existing with an almost insensible condensation. The processes of evolving gas from 

 spring water and from carbonated water are essentially different ; the former taking 

 place by an exaltation of temperature occasioned by the impinging of radiant heat, no 

 kind of decomposition at all going on ; but the latter is accompanied by a true decom- 

 position, due to the presence of vegetable matter. 



427. This case will be better understood by an analysis of the gas given off from 

 carbonated water. A certain volume of water had its carbonic acid and all other gas- 

 eous impurities expelled by long-continued boiling ; it was then rapidly cooled by refri- 

 geratory processes, and impregnated with pure carbonic acid gas ; being introduced 

 into a matrass (fig. 56) with a bunch of pine leaves, the neck of the matrass dipping 

 under the surface of some mercury contained in a cup, so as to cut off communication 

 with the atmosphere, it was exposed to the sun, the day being very favourable, clear 

 and hot; 47-50 measures of the gas evolved were taken ; a piece of caustic potassa ab- 



