360 Prof. Draper onthe Allotropism of Chlorine 
It remained now to open the shutter of the dark room, the 
tubes having been previously set in such a position that the light 
would fall equally on both. As soon as this was done, the chlo- 
rine 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 movement 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 vapor 
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 de- 
lay may be occasioned in the liquid rising in the tube, the chlo- 
rine of which was exposed to the sun. But, after a time, a mist 
arises in the neighborhood 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 con- 
tracts a tendency to unite with hydrogen which is not possessed 
by chlorine which has been kept in the dark. 
On the Allotropism of Chlorine, or its passive and active states. 
In what then does this remarkable change impressed by indigo 
rays upon chlorine consist? ‘This is the question which immedi- 
ately arises from the phenomena we have had under considera- 
tion. 
To this I answer, that when chlorine has been thus influenced 
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 element- 
ary bodies undergo similar modifications. Many of them can 
exist in no less than three different states, and these peculiarities 
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 allotropic states, 
and infers that all are liable to analogous modifications. He in- 
dicates that the isomerism of compound bodies is due, sometimes 
eh 
