260 M. 0. Lea — Allotropic Silver. 



the halogens. Also it is conspicuous by the remarkable facility 

 with which it passes from the one state to the other. Spring, 

 in the examinations above referred to, used pressures of many 

 thousands of atmospheres. Alio tropic silver is changed readily 

 to normal by the mere pressure of the finger or by a tempera- 

 ture of 100 6 C. 



One form of allotropic silver has the property of solubility 

 in water. The solution of a solid in a liquid is often accom- 

 panied by change to a more simple molecular structure. 

 Hitherto the only solvent known for a metal has been another 

 metal, and the behavior of metals when so dissolved has been 

 the subject of late years of very interesting examinations by 

 several chemists. Ramsay* examined the lowering of the 

 vapor pressure of mercury by other metals dissolved in it. 

 Heycock and Neville examined the fall in the freezing point 

 of metals, more especially of tin, caused by the solution in it 

 of other -metals. f Both of these investigations led directly to 

 the conclusion that in the case of a dilute solution of one metal 

 in another, the dissolved metal existed in the atomic form. (In 

 each case a few n^etals gave exceptional results, but silver was 

 not among these.) Tammann's investigations on the alloys 

 of mercury led to precisely similar general deductions. Great 

 weight attaches to conclusions supported in these several ways. 



The fact that a metal in dissolving in another metal appears 

 to assume the atomic form affords no positive proof that it does 

 the same in dissolving in water. In fact the solution of a 

 metal in water is something so new that we have little ground 

 for argument by comparison. So far, however, as the above 

 mentioned analogy may be considered to go, it rather tends to 

 the view that the solubility of silver may be due to its having 

 assumed a very simple and perhaps an atomic form. It may 

 be said therefore that all considerations tend to show that the 

 allotropic forms of silver taken as a whole have a more simple 

 molecular nature than what I have described as the interme- 

 diate form, and that this again is more simply constituted than 

 ordinary silver. 



In the present case we have to consider three distinct forms, 

 (1) allotropic, (2) intermediate, (3) ordinary silver. We notice 

 that (1) can with the utmost facility and in several ways be 

 converted into (2) and (3), and that (2) can always be converted 

 into (3), but that these transformations can by no possibility 

 be reversed. To convert ordinary silver into allotropic we 

 must as a first step dissolve it in an acid : that is, convert it 

 from a polymerized to an atomic form, and only from this 

 atomic form can allotropic silver be obtained. 



* R. Trans.. 1889, p. 521, also Wiedemann, Referate 1889, p. 993. 

 f Jour. Chem. Soc, 1890, p. 376.— Nature, Jan. 1891, p. 262. 



