Page:EB1911 - Volume 18.djvu/219

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200
METAL
  
Name of Metal. Specific Gravity.
Barium   3·75
Zirconium   4·15
Vanadium, powder   5·5
Gallium   5·95
Lanthanum   6·163
Cerium   6·68
Antimony   6·62
Chromium   6·50
Zinc, ingot   6·915
Zinc, rolled out   7·2
Manganese   7·39
Tin, cast   7·29 to 7·299
Tin, crystallized by electrolysis from solutions   7·178
Indium   7·42
Iron, chemically pure, ingot   7·844
Iron, thin sheet   7·6
Iron, wrought, high quality   7·8 to 7·9
Nickel, ingot A   8·279
forged   8·666
Cadmium, ingot   8·546
Cadmium, hammered   8·667
Cobalt   8·6
Molybdenum, containing 4 to 5 % of carbon   8·6
Copper, native   8·94
Copper, cast   8·92
Copper, wire or thin sheet   8·94 to 8·95
Copper, electrotype, pure   8·945
Bismuth .   9·823 at 12°
Silver, cast . 10·4 to 10·5
Silver, stamped . 10·57
Lead, very slowly frozen 11·254
Lead, quickly frozen in cold water 11·363
Palladium 11·4 at 22·5°
Thallium 11·86
Rhodium 12·1
Ruthenium 12·26 at 0°
Mercury, liquid 13·595 at 0°
Mercury, solid 14·39 below −40° 
Tungsten, compact, by H2 from chloride vapour  16·54
Tungsten, as reduced by hydrogen, powder 19·13
Uranium 18·7
Gold, ingot . 19·265 at 13°
Gold, stamped . 19·31 to 19·34
Gold, powder, precipitated by ferrous sulphate 19·55 to 19·72
Platinum, pure 21·50
Iridium 22·2
Osmium 22·477

Thermal Properties.—The specific heats of most metals have been determined. The general result is that, conformably with Dulong and Petit’s law, the “atomic heats” all come to very nearly the same value (of about 6·4); i.e. atomic weight by specific heat=6·4. Thus we have for silver by theory 6·4/108=·0593, and by experiment ·0570 for 10° to 100° C.

The expansion by heat varies greatly. The following table gives the linear expansions from 0° to 100° C. according to Fizeau (Comptes rendus, lxviii. 1125), the length at 0° being taken as unity.

Name of Metal. Expansion
0° to 100°
Platinum, cast ·000 907
Gold, Cast ·001 451
Silver, cast ·001 936
Copper, native, from Lake Superior ·001 708
Copper, artificial ·001 869
Iron, soft, as used for electromagnets ·001 228
Iron, reduced by hydrogen and compressed ·001 208
Cast steel, English annealed ·001 110
Bismuth, in the direction of the axis ·001 642
Bismuth, at right angles to axis ·001 239
Bismuth, mean expansion, calculated ·001 374
Tin, of Malacca, compressed powder ·002 269
Lead, cast ·002 948
Zinc, distilled, compressed powder ·002 905
Cadmium, distilled, compressed powder ·003 102
Aluminium, cast ·002 336
Brass (71·5 % copper. 28·5 % zinc) ·001 879
Bronze (86·3% copper, 9·7% tin, 4·0% zinc)  ·001 802

The coefficient of expansion is constant for such metals only as crystallize in the regular system; the others expand differently in the directions of, the different axes. To eliminate this source of uncertainty these metals were employed as compressed powders. The cubical expansion of mercury from 0° to 100° C. is ·018153 =1/55·087 (Regnault) (See Thermometry.)

Fusibility and Volatility.—The fusibility in different metals is very different, as shown by the following table, which, besides including all the fusing points (in degrees C.) of metals which have been determined numerically, indicates those of a selection of other metals by the positions assigned to them in the table.

Name of Metal. Melting Point. Boiling Point.
Mercury   −38·8  357·3
Caesium   26–27
Gallium 30·1
Rubidium 38·5
Potassium 62·5  719–731
Sodium 95·6  861–954
Iridium   155
Lithium   180·0
Tin   231·9 1450–1600
Bismuth   269·2 1090–1450
Thallium   290
Cadmium   320·7  780
Lead   327·7 1450–1600
Zine   419  929–954
Incipient red heat   525
Antimony   629·5
Magnesium   632·6 about 1100
Aluminium   655
Cherry red heat   700
Calcium   780
Lanthanum   810
Barium   850
Silver   962
Gold  1064
Copper  1082  2100
Yellow heat  1100
Iron 1300–1400
Nickel  1427
Cobalt  1800, (?)
Dazzling white heat 1500–1600
Palladium  1500
Platinum  1760
Rhodium above Pt.
Iridium above 2200
Ruthenium above Ir.
Tantalum In electric
Osmium  furnace

For practical purposes the volatility of metals may be stated as follows:—

1. Distillable below redness: mercury.

2. Distillable at red heats: cadmium, alkali metals, zinc, magnesium.

3, Volatilized more or less readily when heated beyond their fusing points in open crucibles: antimony (very readily), lead, bismuth, tin, silver.

4. Barely so: gold, (copper).

5. Practically non-volatile: (copper), iron, nickel, cobalt, aluminium; also lithium, barium, strontium and calcium.

In the oxyhydrogen flame silver boils, forming a blue vapour, while platinum volatilizes slowly, and osmium, though infusible, very readily.

Latent Heats of Liquefaction.—Of these we know little. The following numbers are due to Person—ice, it may be stated, being 80.

Name of Metal.  Latent 
Heat.
Name of Metal.  Latent 
Heat.
Mercury  2·82 Cadmium  13·6
Lead  5·37 Silver  21·1
Bismuth 12·4 Zinc  28·1

The latent heat of vaporization of mercury was found by Marignac to be 103 to 106.

Conductivity.—Conductivity, whether thermic or electric, is very differently developed in different metals; and, as an exact knowledge of these' conductivities is of great importance, much attention has been given to their numerical determination (see Conduction, Electric; and Conduction of Heat).

The following table gives the electric conductivities of a number of metals as determined by Matthiesen, and the relative internal thermal conductivities of (nominally) the same metals as determined by Wiedemann and Franz, with rods about 5 mm. thick, of which one end was kept at 100° C., the rest of the rod in a “vacuum” (of 5 mm. tension) at 12° C. Matthiesen’s results, except in the two cases noted, are from his memoir in Pogg Ann., 1858, ciii., 428.