EFFECT OF LIGHT ON CHEMICAL COMBINATION. 141 



and set at liberty its oxygen, cannot be considered 

 as at all equalling the power and energy with which 

 a leaf separated from a plant decomposes the car- 

 bonic acid which it absorbs. 



The common opinion, that only the direct solar 

 rays can effect the decomposition of carbonic acid 

 in the leaves of plants, and that reflected or diffused 

 light does not possess this property, is wholly an 

 error, for exactly the same constituents are generated 

 in a number of plants, whether the direct rays of 

 the sun fall upon them, or whether they grow in the 

 , shade. They require light, and indeed sunlight, 

 but it is not necessary that the direct rays of the 

 sun reach them. Their functions certainly proceed 

 with greater intensity and rapidity in sunshine than 

 in the diffused light of day ; but there is nothing 

 more in this than the similar action which light 

 exercises on ordinary chemical combinations ; it 

 merely accelerates in a greater or less degree the 

 action already subsisting. 



Thus chlorine* and hydrogen combining form muri- 

 atic (hydrochloric) acid. This combination is effected 

 in a few hours in common daylight, but it ensues in- 

 stantly, with a violent explosion, under exposure to 

 the direct solar rays, whilst not the slightest change 

 in the two gases takes place in perfect darkness. 

 When the liquid hydrocarburet of chlorine, resulting 

 from the union of the olefiant gasf of the associated 



* Chlorine is a gas named from its green color ; it was formerly 

 called oxymuriatic acid. It has not been decomposed. It is one of the 

 most suffocating of the gases, and highly irritating, even when much 

 diluted with air. It is largely absorbed by water, and the solution has 

 the properly of bleaching. Its solution in water cannot be kept un- 

 changed, as the chlorine unites to the hydrogen of the water and 

 forms muriatic or hydrochloric acid. 



Bleaching salts are formed by exposing lime to an atmosphere of 

 chlorine. Chlorine is useful for removing offensive odors. A few 

 table spoonfuls of bleaching powder, sprinkled occasionally in privies, 

 and in larger quantities upon heaps of offensive substances, upon the 

 floors of slaughter-houses, <fec. will destroy the unpleasant odor, and 

 at the same time add to the value of the manure. 



For description of chlorine, and the method of procuring it, see 

 Webster's Chemistry^ 3d edit. p. 180. 



i One of the compounds of hydrogen and carbon. 



