1 72 Dr. Draper on the Decompositio7i of Carbonic Acid, 



they are placed in the sunshine, this nitrogen comes off along 

 with the gas liberated from the carbonic acid. 



In the experiment I am now relating, a tube arranged like 

 one of the foregoing five evolved, in the open sunshine, a cer- 

 tain volume of gas which was composed of 

 Oxygen . . . 4;\^ 

 Nitrogen . . . 59 WOO 

 Carbonic acid . 00 J 

 The five tubes were placed in the spectrum in the following 

 colours, and emitted the quantities of gas represented in the 

 following table: — 



The gas in tube 2, which had been in the orange and yellow 

 ray, was then washed with a solution of caustic potash. After 

 this it still measured 19*8, containing therefore no perceptible 

 quantity of carbonic acid. It was next examined for oxygen, 

 and with the following result : — 



Constitution of gas emitted by orange and yellow light: 

 Oxygen . . . S'OOl f Oxygen . . . 40 •4« 



Nitrogen . . . 11-80 ^ or 4 Nitrogen . . . 59*6 

 Carbonic acid . O'Oo J L Carbonic acid . 00*0 



19-80 lOO'O 



The gas evolved by the yellow and green rays was next ana- 

 lysed. Like the former, it underwent no diminution by wash- 

 ing with caustic potash. After this treatment it therefore 

 measured 27*4, and on being examined for oxygen yielded as 

 follows: — 



Constitution of gas emitted by yellow and green light : 

 Oxygen . . . 12-5"| ["Oxygen . . . 45*6 



Nitrogen . . . 14-9 > or ^ Nitrogen . . . 54-4 

 Carbonic acid . 00*0 J j^ Carbonic acid . 00-0 



27-4 100-0 



In explanation of the large and variable amount of nitrogen 

 occurring in these analyses, it will scarcely be necessary to 

 remind the vegetable physiologist that it arises from the mode 

 of conducting the experiment. In order to be absolutely cer- 

 tain that no atmospheric air infilmed the leaves, they were 

 soaked in water, and then, when brought into the sunlight, the 

 nitrogen which had accumulated on their tissues from incipi- 



