THE METALS AND THEIR PROPERTIES Metals.—Metals are substances that have a peculiar high luster, known as metallic luster. They are very dense and, as a rule, very heavy. No light can pass through any of the metals except gold, which can be beat en so fine that a greenish light will pass through it. In color the metals are mostly white, but zinc and lead have a bluish, bismuth a reddish, and calcium a yellowish, color. Gold is yellow, and copper is red. Metals are approximately from five to twen ty times as heavy as water, except magnesia and aluminum, which are lighter than water. The principal qualities of the metals are malleabil ity, or the property of being flattened by blows; ductility, or the property of being drawn into wire; conductiv ity, or the property of transmitting heat; fusibility, or the quality of be ing melted; volatility, or the property of turning into vapors; and hardness. In all of these particulars the metals vary greatly, some of their important characteristics being shown by the fol lowing tables.
The Specific Gravity of metals at a temperature of 15i° C., that is, their weight in comparison with water, is as follows: Platinum in thin wire 21.50 Gold 19.50 Mercury Lead 13.59 ead 11.45 Silver 10.50 Bismuth 9.90 Copper 8.96 8.80Iron 7.79 Tin 7.29 Zinc 6 86-7.01 Antimony 6.80 Aluminum 2 56-2.67 Fusibility. — The fusing point of metals, or the degree of temperature required to melt them into liquid form, is as follows: Mercury 39.44 Tin 227.8 Bismuth 2.58 Lead 325 Zinc 412 Antimony 425 Silver 1 023 Gold 1 091 Copper 1,102 Cast iron 1 530 Conductivity.—In the property of transmitting heat, if silver be taken as a basis at 1,000, copper would be represented by 736, gold 532, tin 145, iron 119, lead 85, platinum 84, bis muth 18.
The handle of a solid-silver spoon placed in hot tea or coffee is a well known illustration of the conductivity of silver.
Malleability.—Gold is highly malle able, and has been beaten into films of which 200,000 are required to make 1 inch in thickness. Silver is also very malleable, and so to a less degree are copper, tin, and platinum.
Ductility.—The most ductile metals are iron, copper, platinum, silver, gold, zinc, tin, and lead, in the order named.
Hardness.—Metals vary in hardness at ordinary temperatures, from mer cury, which is a fluid, to chromium and magnesium, which arc capable of scratching glass and chilled steel.
There are forty-nine elements re garded as metals, but only a few of these are useful in the arts. In addi tion to the metals, however, are a number of mixtures of two or more metals, known as alloys.
Alloys.—The alloys are mixtures or compounds of two or more metals melted together. Thus brass is an alloy of copper and zinc; bronze is an alloy of copper and tin; pewter is an alloy of tin and lead. The metals composing alloys unite in various pro portions, and the properties of the alloys and their application in the arts vary considerably with their com position.
In coinage, the term alloy is used to mean a baser metal mixed with gold or silver to make the combina tion harder. British gold coin con tains 11 parts of pure gold and 1 part of copper. United States gold coin contains in 1,000 parts of coin 900 parts of gold, the alloy being about 9 parts copper and 1 part silver.
An alloy of mercury with any other metal is known as an amalgam.
Alloys are not formed by the chem ical union of their different com ponents, but by the diffusion of one metal through the other en masse. Metals fuse at different degrees of heat, and care should be taken to melt first the metals which melt at the lowest degree of temperature, and to cover these with a flux of charcoal, ground glass, or other material to prevent the volatile metals from evap orating before the union is effected.
For instance, zinc melts at a low degree of heat, and when heated to the point at which copper melts zinc becomes volatile and passes off in fumes; therefore in making brass, which is an alloy of copper with zinc, it is necessary to first melt the zinc under a flux and add the copper slow ly, using no more heat than is neces sary; or to place in the crucible first the zinc, then the copper, and the flux over all.
The harder metals should be finely divided in grains, shavings, or filings so that they will melt more easily. When mixing metals, it is necessary to note all changes that take place and use good judgment. Experience is better than hearsay.
Amalgams. — Metals will usually combine with each other if one of them is in a state of fluidity. Mer cury, being a fluid at ordinary tem peratures, will amalgamate with most of the other metals in the cold, but heat affects the amalgamation more quickly. To amalgamate in the cold, it is only necessary to divide in very small particles, as grains, shavings, or filings, the metal to be united with mercury. To make amalgams by heat, as is necessary with most metals, heat the mercury until it begins to simmer, and raise the grains of metal to be amalgamated to a red heat. Then add them a little at a time.
Gold or silver may be amalgamated with mercury by simply stirring the two metals together with a glass rod and pouring the resulting mixture into cold water. This is the amalgam used for gilding or silvering. After being applied, it is exposed to heat to evaporate the mercury. Lead or tin may be amalgamated by melting either metal, adding an equal weight of mercury, and stirring with an iron or glass rod.
Copper amalgamates with great dif ficulty, and iron not at all; hence iron is the one metal (except platinum) which should be allowed to come in contact with mercury.