III.—PART OF A SILVER VASE.
A sketch of this, of the same size as the original, is annexed; it was distinctly curved, having formed part of a hollow thin vessel.
No. 544. No. 545.
Fragments of a Silver Vase.
No. 544. Convex Surface.
Sepulchre IV. Actual size.
No. 545. Concave Surface.
The total weight of the specimen was 44·36 grains. The metal was much corroded on both surfaces. The convex or outer surface was completely covered with a somewhat irregular crust while the concave or inner surface was only partly covered with a similar crust, and partly with a yellowish tarnishlike film. When broken across, the fractured surface of the crust on both sides of the metal was found to be in two distinct layers; that next the metal was black, dull, somewhat sectile, and easily broken; while the other, or outer layer, was light-grey, soft, sectile, and wax-like. In some places the metal was corroded completely through. The crust was removed by warm dilute ammonia-water and gentle rubbing; the residual metal was found to be very brittle, much pitted on the surface, dull white in fracture, granular, and containing minute irregular cavities; no appearance of fibre or crystalline structure was observed, even with the aid of the microscope. By annealing, the softness and malleability of the metal were restored in a marked degree. The thickness of the specimen, inclusive of the crust on one surface only, was 1-25th of an inch; and where the crust was thickest it was 1-20th of an inch. The thickness of the metal, after the removal of the crust by dilute ammonia-water and rubbing, was 1-40th of an inch.
A portion of the specimen was selected for analysis to which the crust was attached on the convex or outer surface only, and which was comparatively free from crust on the opposite surface; the quantity operated on was 15·786 grains. By repeated treatment with warm moderately strong ammonia-water, gentle rubbing, and washing with warm water, the crust was easily removed; most of it being dissolved by the ammonia-water, which became pale blue, while the insoluble part was left as a brownish black powder, intermixed with some particles of metallic silver. The metal, after this treatment and drying, weighed 11·823 grains. The metal itself (a), the portion of the crust soluble in ammonia-water (b), and the residue insoluble in ammonia-water (c) were separately analysed, with the following results:—
COMPOSITION PER CENT.
| (a) Metal. | Silver | 71·60 | |||
| Gold | 0·22 | ||||
| Copper | 2·42 | ||||
| Lead | 0·33 | ||||
| Iron | 0·09 | ||||
| Chlorine | traces | ||||
| 74·66 | |||||
| (b) Crust. | Chloride of Silver | 19·98 | |||
| Portion soluble in ammonia-water. | Protoxide of Copper (Black Oxide) | } | 0·56 | ||
| Chlorine | 0·15 | ||||
| Copper | 0·13 | ||||
| Sulphuric Acid | traces | ||||
| Carbonic Acid Water | } | 1·15 | |||
| 21·97 | |||||
| (c) Crust. | Gold | 0·05 | |||
| Portion | Silver | 1·36 | |||
| insoluble in ammonia-water. | Protoxide of Copper (Black Oxide) | } | 0·09 | ||
| Carbonate of Lime | 1·36 | ||||
| Silica Peroxide of Iron Alumina | } | 0·30 | |||
| 3·16 | |||||
| 99·79 |
The composition per cent. of the metal, exclusive of the crust, as calculated from the above analysis, is given underneath; but it certainly cannot be inferred that the original metal had the exact composition shown in that analysis, because some of the ingredients may not have been carried away during corrosion in the same relative proportions in which they were present in the original alloy.
COMPOSITION PER CENT.
| Silver | 95·59 |
| Gold | 0·30 |
| Copper | 3·23 |
| Lead | 0·44 |
| Iron | 0·12 |
| 99·68 |
A portion of the crust when heated in a glass tube gave off water, and the glass was stained yellow.
A portion of the crust treated with dilute hydrochloric acid effervesced, the acid became pale blue, and was found to contain copper and lime.
The crust was examined under the microscope, but no trace of crystalline structure could be detected. A qualitative examination was made of a portion of the inner crust, from which it appeared that its composition was similar to that of the outer crust.