MEMOIR XX.] THE ALLOTROPISM OF CHLORINE. 3Q5 



long time, so may a solution of chlorine in water be pre- 

 served. The chlorine is in an inactive state. 



But if anything be done to make the chlorine take on 

 its other form and pass to the active condition if it be, 

 for example, set in the sunshine its affinity for hydro- 

 gen is exhibited and decomposition is the result. 



The qualities thus communicated to the chlorine not 

 being of a transient kind, but remaining for a length of 

 time, we see how it is that after an exposure to the sun 

 decomposition is subsequently carried forward in the 

 dark. 



The indisposition of chlorine to unite with carbon, 

 which has been regarded as a singular quality, is not 

 more remarkable than its indisposition to unite with hy- 

 drogen in the dark. 



If the power assumed by chlorine of uniting with hy- 

 drogen and carbon depends on a change in its electrical 

 relations a passage from the passive to the active state 

 we might expect that those various causes which in 

 the case of other elementary bodies bring about anal- 

 ogous changes, and throw them from one allotropic con- 

 dition to another, would here also exercise a perceptible 

 action. Among such causes we may enumerate the ac- 

 tion of a high temperature and the contact or presence 

 of other bodies. 



It may be remarked, in the instances to which Berze- 

 lius has referred, that exposure to a high temperature is 

 one of the most frequent causes of allotropic change. In 

 the case of chlorine the remark holds good, for, as is 

 well known, when a mixture of chlorine and hydrogen is 

 passed through a red-hot tube, hydrochloric acid forms 

 with rapidity. The high temperature, therefore, impress- 

 es on chlorine the same tendency to unite with hydrogen 

 which is communicated by the solar rays. 



But the contact of other bodies frequently determines 



U 



