Fusibility

In forming alloys of metals, they do not combine with each other in their solid state (with the exception of mercury), owing to their chemical affinity being counteracted by the force of cohesion; and in order to form combinations of them, it is necessary to liquefy at least one of them, in which case they will nite, provided they have a chemical affinity for each other: thus bell-metal and brass are formed when pieces of tin or zinc are put into molten copper; and in the formation of alloys of this nature, where one of the metals is more fusible than the other, the less fusible metal should be fused first, and the more fusible metal added either in the molten or solid state. As the fusible metals are added, the temperature of the alloy should be reduced, to prevent oxidation or burning away of the fusible metals; for this reason, it is better to add the more fusible metals in the solid state, as by so doing the temperature of the metal is decreased. Alloys are always more fusible than the less fusible metals of which they are composed, and in some cases are more fusible than the most fusible metal they contain, as is the case in alloys of tin, lead, and bismuth.

Some founders, in order to have the metal thoroughly united, first fuse the metals together, cast them into ingots, and remelt them for use. This practice is bad, for in the after-fusion there is always more or less of the more fusible metal burned away; and it is hard to determine the proportions of the alloy, or to have any certainty as to the quality of the castings. In melting ingots or scrap-alloys, they should be fused as rapidly as possible, and at the lowest available temperature, so as to avoid oxidation.

Some metals are almost infusible, and, when heated to the highest heat in a crucible, they refuse to melt and become fluid; but any metal can be melted by combination with the more fusible metals. Thus platinum, which is infusible with any ordinary heat, can be fused readily when combined with zinc, tin, or arsenic. This metal, by combination with arsenic, is rendered so fluid that it may be cast into any desired shape, and the arsenic may then be evaporated by a mild heat, and leave the platinum. Nickel, which barely fuses alone, will enter into combination with copper, forming German silver-an alloy that is more fusible than nickel and less fusible than copper. This alloy is rendered the whiter, harder, and less fusible, the more nickel is added. The less fusible metals, when fused in contact with the more fusible metals, seem to dissolve in the fusible metals; rather than melt, the surface of the metal is gradually washed down, until the entire mass is dissolved or liquefied, and reduced to the state of alloy.

In forming alloys of brass, in furnaces where heat enough cannot be obtained to fuse the copper separately, the alloy may be formed by heating the copper to the highest heat, and then adding the zinc or tin in the molten state, so as not to reduce the temperature of the copper.

In forming alloys with new metals, it is usual to melt the less fusible metals first, and then add the more fusible metals, and mix them by stirring well together; the rod used in stirring them should be heated to redness to prevent lowering the temperature or chilling the metal. In mixing alloys for bells, the alloy should be well stirred with an iron rod well heated, in which case part of the iron is dissolved, combines with the alloy, and gives the bell a better tone; but alloys of brass that are to be turned or finished should never be stirred with an iron rod, for the iron dissolved from the rod will cause hard specks in the alloy, if not thoroughly mixed. In forming fine alloys, the alloy should be stirred with a rod of the least fusible metal contained in the alloy, or with a wooden stick; the wooden 6tick, in many cases, is better than a metallic rod, for it causes the metal to boil slightly and units more thoroughly, but it cannot be used in a little crucible with only a small amount of metal.

When alloys are made that contain only a very slight quantity of a metal that is difficult to fuse, as in pewter, it is scarcely possible to throw into the melted tin the 1/2 per cent. of melted copper, with any certainty of the 2 metals being properly combined; and in forming this alloy, it is customary to melt the copper in a crucible, and then add to it 2 or 3 times its weight of melted tin; this dilutes the copper, and makes an alloy called temper or hardening. This alloy is very fusible, is melted in an iron ladle, and is added to molten tin or lead, to give it the desired hardness, and form pewter. (E. Kirk.)

Following are the fusing-points of the principal metals and other elements employed in alloys :-

Aluminium

• •

• •

1292° F.

• •

(700° C.)

Antimony

• •

• •

797° F.

• •

(435° C.)

Arsenic

• •

• •

773° F.

• •

(412° C.)

Bismuth

• •

• •

504° F.

• •

(270° C.)

Cadmium

• •

• •

608° F.

• •

(320° C.)

Copper

• •

• •

1922° F.

• •.

(1060° C.)

Gold

• •

• •

2282° F.

• •

[1250°C.)

Iron, cast

1922o-2192°F

(1060°-1200°C.)

,, steel

• •

2372°-2562°F.

(1300°-1400°C.)

,, wrought

2732°-2018o

(1500°-1600°C.)

Lead

• •

• •..

• •

628°F.

• •

(330° C.)

Mercury

• •

• •

-40oF.

• •

(-40°C.)

Nickel

• •

• •

2702°-2012°F.

(1500°-1600° C.}

Phosphorus

• •

111° F.

• •

(44° C.)

Platinum

• •

• •

4712oF.

• •

• •

(2600° C.)

Silver

• •

• •

• •

:632°F.

(1000° C.)

Sulphur

> • •

• •

• •

239° F.

• •

(115° C.)

Tellurium

• •

• •

716°F.

• •

(380° C.)

Tin

•• •

• •

• •

456°F.

• •

(235° C.)

Zinc

• •

• •

• •

773° F.

• •

(412° C.)

(Bayley.)