284 Mr. Hunt on ActinchChemistrj/. 



state (17.) than the chloride; and that the well-known acce- 

 lerating power of moisture is due to the decomposition of 

 water, and the influence of the nascent hydrogen, in reducing 

 the argentine salt. 



28. The principal point was now to ascertain the condition 

 of the chloride of silver after it had been thoroughly darkened 

 by exposure. Many experiments were tried, in various ways, 

 which need not now be detailed, as they were in varying de- 

 grees successful; to one alone which gave very satisfactory 

 results I shall at present confine myself. Pure chloride of 

 silver was prepared with great care, as before stated (21.), well- 

 washed with boiling distilled water, until neither nitrate of 

 silver nor muriatic acid produced any precipitate, and then 

 dried. Five grains of the salt were put into a long test-tube 

 full of distilled water, and placed in the sunshine to darken, 

 the powder being frequently moved that every part might be 

 acted upon by the sun's rays. It was found, even after an 

 exposure of a few minutes, that the water contained chlorine; 

 it became opake on the addition of nitrate of silver, and this 

 very gradually increased as the chloride darkened. The 

 darkening was continued for several hours, after which the 

 solution was filtered to free it from chloride of silver, and 

 nitrate of silver added to the filtered fluid ; chloride of silver 

 was precipitated, which, when collected and dried, weighed 

 1*4 grain on one occasion, 1 grain on another, and 1*5 grain 

 on a third trial. It is very difficult to ensure the darkening 

 of every portion of the chloride of silver, it adheres in little 

 masses ; these are darkened on their outer surface, and the in- 

 terior is then protected from the solar influence; this was over- 

 come as much as possible by repeatedly breaking down those 

 small particles with a glass rod. On drying the darkened 

 chloride and weighing, it was found that the loss of weight 

 was scarcely a quarter of a grain. From this it is evident that 

 the chlorine liberated by the sun's rays must have been partly 

 replaced by some other body ; and it becomes highly probable 

 that the darkened chloride is in the state of an oxychloride. 

 No oxide of silver could be detected by digestion in diluted 

 nitric acid. 



29. The exposure in the water was in another case conti- 

 nued for many days, but no greater degree of darkening oc- 

 curred ; but a curious fact was now noticed. It was found that 

 during the night nearly all the chlorine which had been libe- 

 rated during the day was recombined, and that the darkened 

 powder became much lighter. A similar effect to this, but a 

 more striking one, has been noticed by Dr. Percy and Mr. 

 Shaw, when chloride of silver is darkened by light in an at- 



