Fig. 20. Ingot Mould.
The bar of metal upon cooling should be weighed, and the difference—as most meltings show a little—noted. This is loss, but it will be very little, if the above instructions have been strictly adhered to from the beginning of the operation. With the charcoal flux we have referred to, very nice and clean bars of metal can be produced. This flux is always floating upon the surface of the mixture, and, with a little dexterity in the pouring, it can be prevented from coming out of the crucible with the metal; its proper place is at the end of the pouring. When tin is employed, either in alloys or solders, its treatment is similar to that described for zinc; such alloys should not be kept too long in the furnace after they have become fused, as they rapidly become oxidized, especially if brought into contact with the air.
The waste in silver, and in fact of all alloys, is entirely dependent on the duration of the time of fusion. If it is prolonged after the addition of the fusible metals, the loss is greater in every case, than when once melted. The metals should be subjected to the beat of the furnace for the shortest possible period. The alloys of silver with zinc would lose more than the alloys of silver with tin, because zinc rapidly volatilises when heated above the temperature of its fusion, and this is especially the case when it enters into combination with silver and copper in the fused state; its vapours can be seen to rise and burn in the air, producing light and white flaky fumes, and, chemically speaking, forming the protoxide of zinc. With care and manipulative skill during the process of fusion, the proportion of waste can be reduced to a minimum; and when this is exactly ascertained an allowance can be made in the preparation of the mixture for the crucible. From the above remarks it will be apparent that when both tin and zinc form component parts of a mixture, either to be used as an alloy or as solder, the tin should be added to the other metals, and well stirred, so as to obtain an intimate mixture, before the addition is made of the zinc.
Scrap silver should be carefully sorted before undergoing the process of re-melting, and if possible all foreign substances removed. It may, if preferred to work it in that way, be melted into a separate bar, or otherwise used as an addition to a new mixture. When, however, it is separately melted, a flux, such as carbonate of soda, may be employed, on account of its cheapness, in small proportions to the charcoal flux already alluded to. In brittle and troublesome alloys we have found charcoal and a small quantity of borax extremely effective. Saltpetre is a very useful flux in dissolving impurities, but in some alloys its presence is injurious. Sandiver will remove iron or steel from the mixture. Corrosive sublimate destroys lead and tin. We have found the sub-carbonate of potash one of the best fluxes for silver, when matters have not been quite so straight as they should be in the working of the metal; it is used in melting the difficult alloy of 18-carat gold, and is considered a secret not generally known to the trade. Sal-ammoniac is an excellent flux for producing clean and bright ingots and tough alloys. We invariably use it with all our alloys, mixed in small quantities with charcoal, and prefer it to all others.
Lemel, that is the filings and turnings produced during the process of manufacture, should have quite a separate method of treatment. It is best prepared for the crucible by passing it through a fine sieve, afterwards thoroughly burning it in an iron ladle, and then intimately mixing it with a flux of the following nature and proportions:—
| Silver dust | 24 | parts |
| Carbonate of soda | 4 | ” |
| Common salt | 2 | ” |
| Sal-enixum | 1 | ” |
| 31 | parts. |
