Silver objects found in Mycene are said by Mitzopulos[73] to show three layers, the outermost of which has a red colour and is not markedly friable, consisting of silver oxide; the second is tough and consists of silver chloride (horn-silver); while the third, that next to the metal, is similar to the outermost layer. Mitzopulos thinks that the chlorine must have been brought by rain water, since there are neither sea nor springs of water in the neighbourhood.
Schertel[ [74] distinguished two layers in fragments of silver from the Hildesheim silver find, the outermost of which proved to be silver chloride:
| Silver | 75·43% found, 75·31% calculated for AgCl |
| Chlorine | 24·51% found, 24·69% calculated for AgCl |
Beneath this layer was a very thin, almost black, brittle layer of silver subchloride:
| Silver | 87·0% found, 85·89% calculated |
| Chlorine | 12·8% found, 14·11% calculated |
Between the metal and the latter layer was a small quantity of dark powder, which Schertel recognized as gold. He thinks that the layer of silver subchloride seems to indicate that the water, which permeated the surrounding clay, contained chlorides, and first converted the copper into copper chloride; that the copper chloride together with the silver then formed silver subchloride and cuprous chloride. Should the subchloride again become chloride, it would be able to attack the silver afresh. The slowness of the process, when the silver and copper in association with it had been converted into chlorine compounds, allowed the gold to be deposited as a fine powder upon the intact metal.
A silver coin rolled out into a thin plate, after remaining in a solution of common salt for six months, was found to have lost 27·7% of its copper, so that the plate became brittle, especially in those parts where it was thinnest.
Bibra[75] gives a similar explanation of the conversion into silver chloride. He believes that the reddish colour which is occasionally seen on silver at a fresh fracture must be due to the presence of cuprous oxide.
The following extract is taken from the section which deals with silver in the work of Berthelot[76] previously quoted:
“Silver chloride is for the most part produced by the sodium chloride dissolved in the subsoil water, which acts in conjunction with the oxygen and the carbonic acid of the air: