LIGHT CARBURETTED HYDROGEN. 49 



gas thus pioduceo is known by the name of carbonic oxide. It consists 

 of one equivalent of carbon united to one of oxygen, and is represented 

 by C2 O2, or simply CO. 



This gas is colourless, without taste or smell, lighter than common air, 

 nearly insoluble in water, extinguishes flame, does not support life; 

 burns in the air or in oxygen gas with a blue flame, and during this 

 combustion is converted into carbonic acid. It is produced along with 

 carbonic acid during the imperfect combustion of coals in our fires and 

 furnaces, but is not known to occur in nature, or to minister directly to 

 the growth of plants. 



There exists a general relation among the three compounds of carbon 

 and oxygen above described, to which it may be interesting to advert, 

 in connection with the subject of vegetable physiology. This relation 

 appears when we compare together their chemical constitution, as re- 

 presented by their chemical formulae : — 



Carbonic acid consists of one of carbon and two of oxygen, or CO2 ; 



Carbonic oxide, of one of carbon and one of oxygen, or CO ; 



So that if carbonic acid be present in a plant, and be there deprived 

 of one e(juivalent of its oxygen, by any vital action, it will be converted 

 into carbonic oxide. 



Oxalic acid consists of two of carbon and three of oxygen, or C2O3. 



If wc add together the formulae for 



Carbonic acid = COg and 

 Carbonic oxide = CO, we have 



Hence this acid may be formed in the interior of plants, either by the 

 direct union of carbonic oxide and carbonic acid, or by depriving two of 

 carbonic acid (2CO2 or C2O4) of one equivalent of oxygen. 



When in a subsequent lecture we have studied the structure and func- 

 tions of the leaves of plants, we shall see how very easy it is to under- 

 stand the process by which oxalic acid is formed and deposited in the in- 

 terior of plants, and by which carbonic oxide also may be, and probably 

 is, produced. • 



§ 4. Light carburetted hydrogen — the gas of marshes and of coal mines. 



During the decay of vegetable matter in moist places, or under water, 

 a light inflammable gas is not unfrequently given off, which differs in its 

 properties from any of those hitherto described. In summer it may often 

 be seen rising up in bubbles from the bottom of stagnant pools and 

 from marshy places, and may readily be collected. 



This gas is colourless, without taste or smell, and is little more than 

 half the weight of common air, [its specific gravity, by experiment, is 

 0-5576.] A lighted taper, plunged into it, is immediately extinguished, 

 while the gas takes fire and' burns with a pale yellow flame, yielding 

 more light, however, than pure hydrogen gas, which it otherwise re- 

 sembles. Animals introduced into it, instantly cease to breathe. 



It consists of one equivalent of carbon (C) united to two of hydrogen 

 (2H or H2), and is represented by CHg. When burned in the air or 



