as connected iioith the Theory of Substitutions. 339 



tubes having been previously set in such a position that the 

 light would fall equally on both. As soon as this was done, 

 the chlorine which had been exposed to the sun united at once 

 with its hydrogen, and the water rose in the tube c. But in 

 the other, which had not been exposed to the sun, no move- 

 ment took place until the gases had had time to be affected by 

 the light coming through the open shutter. 



When care has been taken to have the gases made quite 

 dry, and, owing to the narrowness of the tube c, no aqueous 

 vapour has had time to contaminate the gas in B, so that no 

 water is present to condense the chlorohydric acid as it forms, 

 a little delay may be occasioned in the liquid rising in the tube 

 the chlorine of which was exposed to the sun. But after a 

 time a mist arises in the neighbourhood of the water in the 

 narrow tube, due to the chlorohydric acid condensing, and 

 then the process goes forward with regularity. 



It appears, therefore, that chlorine, by exposure to the sun, 

 contracts a tendency to unite with hydrogen, which is not pos- 

 sessed by chlorine which has been kept in the dark. 



Qn the Allotropism of Chlorine, or its Active afid Passive. 



States. 



In what then does this remarkable change, impressed by in- 

 digo rays upon chlorine, consist? This is the question which 

 immediately arises from the phsenomena we have had under 

 consideration. 



To this I answer, that when chlorine has been thus influ- 

 enced, its electro-negative properties are exalted, and it has 

 passed from an inactive to an active state. 



It is now fully established that a great number of the ele- 

 mentary bodies undergo similar modifications. Many of these 

 can exist in no less than three different states, and these pe- 

 culiarities are impressed on the compounds to which they give 

 rise. To these peculiarities Berzelius has recently directed 

 the attention of chemical philosophers, in his paper on the 

 Allotropism of Simple Bodies, and its Relation with certain 

 cases of Isomerism in their Combinations. He shows, that of 

 the elementary bodies now known, many undoubtedly exist in 

 several allbtropic states, and infers that all are liable to ana- 

 logous modifications. He indicates that the isomerism of 

 compound bodies is due, sometimes to the different modes in 

 which the atoms of which their constituent molecules consist 

 are grouped, and sometimes to the different allotropic states 

 in which one or other of those elements is found. Thus, as 

 M. Millon has remarked, the intrinsic difference between car- 

 buretted hydrogen gas (CH) and otto of roses (CH), which 



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