10 PROCEEDINGS OP THE AMERICAN ACADEMY 



silver to the litre of boiling wash- water would certainly prevent all 

 action. 



A few drops of hydrochloric acid added to the wash-water greatly 

 diminishes its solvent action on flaky chloride of silver, but does not 

 wliolly prevent it, as is evident from the fact shown in the table below, 

 that hydrochloric acid does not precipitate chloride of silver from its 

 solution in water nearly as effectually as nitrate of silver; and, as is 

 well known, hydrochloric acid, if in any considerable excess, exerts a 

 strong solvent action on the precipitated chloride. 



As shown by Stas, the precipitation of chloride of silver, from its 

 solution in hot water by the reagents we have named, depends solely 

 on the change which the reagents produce in the solvent. That the 

 action is an example of simple solution is shown by the fact that a 

 considerable portion of the chloride of silver dissolved in boiling water 

 is deposited when the solvent cools. This phenomenon is a striking 

 one, and can easily be observed by pouring into a glass crystallizing 

 pan some of the clear solution obtained in the experiment described 

 above. As the water cools it becomes cloudy, and deposits a granular 

 powder, which adheres to the bottom of the glass. The grains are 

 usually very small ; but if the solution cools slowly the crystalline 

 form can readily be distinguished under the high powers of a good 

 microscope, and the little cubes present all the characteristics of the 

 native crystals of chloride of silver. It is evident, therefore, that the 

 granular condition of chloride of silver is a crystalline condition, and 

 this experiment may elucidate the manner in which the native crystals 

 are produced. 



We have thus far only spoken of the solubility of cliloride of silver 

 in boiling water. As is evident fi-om the crystallization just described, 

 the solubility rapidly diminishes as the temperature falls ; but even at 

 the ordinary temperature the solubility is distinctly marked. Luke- 

 warm water poured on and off freshly precipitated chloride of silver, 

 becomes decidedly opalescent on the addition of niti-ate of silver, and 

 even if cold water is used the opalescence is perceptible. 



In order to obtain an approximate measure of the effects we have 

 described, Mr. Hyams precipitated about fifteen grammes of chloride of 

 silver, and, after thoroughly washing it, boiled the precipitate with a 

 larjie volume of water in a ch^ss flask. At the end of an hour he 

 decanted through a filter about one litre of the boiling water, and, 

 having divided the filtrate into two portions, he added to one portion 

 nitrate of silver, and to the other, hydrochloric acid. Tlie precipitated 

 chloride of silver was in each case collected and weighed. At the end 



