M. C. Lea — Solutions of Metallic Silver. 343 



Aet. XLIX. — On Solutions of Metallic Silver • by 

 M. Caeey Lea. 



The solutions of metallic silver which I have described in 

 previous numbers of this Journal are all colloidal. Since pub- 

 lishing those papers I have examined all the varieties with the 

 result that none of them will pass through membranes. One 

 of these forms of silver solution, that obtained by the action 

 of ferrous citrate has also been examined by Mr. Prange and 

 by Dr. Barus with the same result. 



The silver solutions are colloidal. But as to whether they 

 are polymerized seems doubtful. Polymerized substances 

 have this property in common that they are more indifferent 

 than the same substances in their ordinary molecular condition. 

 ISTow all the varieties of allotropic silver including the soluble 

 form are more easily oxidized and chlorized than is silver in 

 its ordinary form. This does not look like polymerization. 



These colloidal solutions of silver are at the least as perfect 

 as those of any other perfectly soluble colloidal substance. A 

 good way of testing for perfect solubility is to observe the 

 liquid under a skylight, letting the incident light make a right 

 angle with the line of view. Many substances which viewed 

 by transmitted light are not only transparent but brilliantly 

 clear, when examined in the manner just mentioned show 

 unmistakable turbidity. 



The solutions of silver stand this test perfectly. This exper- 

 iment seems to disprove the conclusion arrived at by Drs. Barus 

 and Schneider that this form of silver is not allotropic but 

 ordinary silver in a state of very fine division. (Zeitschrift 

 fur Physikalische Chemie, viii, 298.) When carefully made 

 they are also very permanent. I have some silver solution 

 made by the action of alkaline hydroxide and dextrine which, 

 after three years standing, is still strongly colored. A consid- 

 erable part of the silver has separated but as this separation 

 has taken place in the form of bright white metallic silver and 

 has occurred where the light was strongest (the bottle having 

 stood on a table in a well lighted room) the change seems to 

 have been due principally if not wholly to the action of light. 



This solution thus maintained so long seemed to afford an 

 opportunity for the rigorous determination of its colloidal 

 nature. Placed in a dialyzer at the end of two weeks not a 

 trace had passed through. 



These results seem to lead to the conclusion that the silver 

 solutions are colloidal and yet of a very perfect character inas- 

 much as they will bear the same tests for absolute transparency 

 as solutions of crystalloids. 



