ON THE CRYSTALLINE STRUCTURE OF METALS. 
297 
rate all over, but at different rates over different crystals, in such a way as to produce 
marked differences of level between adjacent crystals. Another phenomenon, seen 
best in etching lead in dilute nitric acid, is also of interest in this connection ; it has 
already been described in the present paper (see p. 284). We there have a case of 
lead dissolved from one crystal and deposited upon another crystal in its proper 
orientation. 
In view of these facts, we think it must be admitted that different crystal faces, 
having a different orientation of their elements, differ in solubility in the same solvent. 
To inquire into the cause of this difference is a further step in speculation which is, 
perhaps, hardly necessary in this connection. Such differential actions may, however, 
most probably be attributed to differences of electrical potential in the surfaces 
involved. If we accept this view of the matter, then the diffusion across films of 
eutectic becomes a case of electrolysis. Now, while diffusion in metals and alloys is 
a proved fact, the possibility of electrolysis in an alloy has not yet been demonstrated 
experimentally. # On the other hand, the close analogy with salt solutions leads one 
to expect that alloys could be electrolysed, and those who have experimented in the 
matter are not by any means certain that greater experimental resources will not 
enable them to electrolyse alloys. 
There is at least one fact in the phenomena of re-crystallisation which the solution 
theory, apart from electrolysis, does not cover, while the electrolytic theory explains 
it very readily. We refer to the fact that only strained crystals will grow, while 
unstrained crystals show no tendency to change even at higher temperatures. The 
explanation, on the electrolytic theory, is that in the unstrained state the crystals are 
surrounded by practically continuous films of eutectic, and that electrolysis only 
becomes possible when severe distortion has broken through these films in places, 
allowing the actual crystals to come into contact ; the electrolytic circuit would then 
be for each pair of crystals, from one crystal to the other by direct contact and back 
through the eutectic film. 
Our view of the phenomena of re-crystallisation in solid metals may be summed up 
thus.:—We believe that the action is one of solution and diffusion of the pure metal 
constituting the crystals into the fusible and mobile eutectic forming the inter- 
crystalline cement. This diffusion results in the growth of one crystal at the expense 
of the other, owing to differences in solubility of the crystal faces on opposite sides of 
the eutectic film, and it seems probable that this phenomenon of directed diffusion is 
really a form of electrolysis. 
* It has, however, been shown by Gaknier (‘Comptes Bendus de l’Academie des Sciences,’ vol. 116, 
1893, pp. 144-9), that the diffusion of carbon into iron is affected by the action of an electric current. He 
interposed a layer of carbon between two iron electrodes enclosed in a fire-clay tube; the whole was 
heated to 1000° C., and a current of 55 amperes was passed for three hours, when the anode was found 
to be unchanged, while the cathode had undergone considerable cementation. This action in the interior 
of the iron is practically electrolysis of the carbon-iron eutectic. 
VOL. CXCYL-A. 2 Q 
