In making alloys, especially where the component metals vary greatly in fusibility and volatility, the following rules must be observed:
1. Melt the least fusible, oxidable and volatile first, and then add the others heated to their point of fusion or near it. Thus if we desire to make an alloy of exactly one part copper and three zinc, it will be impossible to do so by putting these proportions of the metals in a crucible and exposing the whole to heat. Much of the zinc would fly off in vapor before the copper was melted. First melt the copper and add the zinc which has been melted in another crucible. The zinc should be in excess, as some of it will be lost anyway.
2. Some alloys, as copper and zinc, copper and arsenic, may be formed by exposing heated plates of the least fusible metal to the vapor of the other. In making brass in the large way, thin plates of copper are dissolved as it were in melted zinc until the proper proportions have been obtained.
3. The surface of all oxidable metals should be covered with some protecting agent, as tallow for very fusible ones; resin for lead and tin; charcoal for zinc, copper, etc.
5. If possible, add a small portion of old alloy to the new one. If the alloy is required to make sharp castings, and strength is not a very great object, the proportion of old alloy to the new should be increased. In all cases a new or thoroughly well cleaned crucible should be used.
Known also as "British plate," "electrum," etc. It is a favorite material for making articles that are to be electrotyped. The best proportions of the ingredients are copper, 20; nickel, 4; zinc, 16.
Lead, 9; antimony, 2; bismuth, 1. This alloy is sometimes called "mock iron;" it expands in cooling, so that when a hole is filled with the melted alloy, the plug is not loose when it is cold.
The following composition may be cast on steel or iron, and will adhere firmly thereto. Its rate of expansion is nearer that of iron and steel than any similar compound. When cast around iron or steel therefore, it closes firmly around them and does not become loose by alternate expansion and contraction. It consists of tin, 3; copper, 3 1/2; zinc, 7 1/2. Since the last metal is partly converted into vapor at a high temperature, the above proportion may be slightly increased.
Copper, 90; aluminium, 10. Resembles gold in color, and is very strong and durable.
Copper, 70; nickel, 23; aluminium, 7. Has a beautiful color and takes a high polish.
1. Lead, 2 oz.; tin, 2 oz.; bismuth, 2 oz.; mercury, 4 oz. Melt the first three and add the mercury. The glass being well cleaned, is carefully warmed and the melted amalgam is poured in and the vessel turned round until all parts are coated. At a certain temperature this amalgam adheres readily to glass.
2. Bismuth, 8; lead, 5; tin, 3; mercury, 8. Use as directed for No. 1.