Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/79

Rh METALS 69 Bismuth, Lead. Lead, Silver. Gold, Silver. BI Pb

Pb Ag e Au Ag e 6020 16 12 8 4 2 1 1 1 1 1 1 1 1 1 1 1 1 2 3 4 5 12 50

-003 -005 007 -014 024 -040 031 -020 -015 -010 -004

l l 1 2 4 10 25 4 2 1 1 1 1 -005 -003

+ 003 + -oo&amp;lt;; + 004 + 002 1 1 1 1 2 4 C 6 4 2 1 1 1 1 -004 -004 -004 -002 -0025 -0027 --00-J4 Mercury, Tin. Mercury, Lead. Hg Sn e Hg Pb e l l 2 o 1 1 - -009 -005 -007 1 1 2 2 1 1 + 002 010 016 To make these numbers trustworthy it would lie necessary to de termine their probable errors ; and this Matthiesen has not done. It would appear that any value of e from to (say)db 002 counts for nothing, and anything up to 004 certainly must be taken as not proving much either way. If this is correct, then (1) No contraction or expansion is proved iu the cases Sb, Bi; Cd, Bi ; Cd, Pb ; Au, Ag ; (2) A contraction (from 5 to 47 per cent.) is proved for Sn, Ag; Bi, Ag ; Bi, Au; Pb, Au; Pb, Bi; Hg, Su ; Hg, Pb; Sn, Bi(?); Au, Ag (?); (3) An expansion (from 5 to 8 percent.) is proved for Sb, Sn; Sb, Pb ; Sn, Cd (?); Sn, Pb (?); certain cases of Sn, Au and Pb, Ag ; (4) In the two series Sn, Au and Pb, Ag, there are cases both of expansion and of contraction. Thermic and Electric Projxrtics. The specific heat of an alloy, so far as we know, is always in approximate accordance with Dulong and Petit s law. Thus the specific heat of C^A^ is (5+1) x 6-4 5x63-5+1x27 with about the same degree of correctness as the constant &quot; 6 4 can claim for itself. Expansion. Matthiesen, from numerous determinations made with alloys and their components, concludes that the expansion of an alloy (from to 100 C.) is nearly equal to the sum of the ex pansions of its components. Supposing, for instance, one volume of gold to expand (from to t) by o, and one volume of silver by /8; then an alloy of four volumes of gold and three volumes of silver expands by (4o + 3)/7 per unit. Fusibility. In the case of an alloy the melting-point and the freezing-point are, in general, separated by a greater or less interval of temperature, and the latter in itself may have two values as shown by Rudberg, who found that when a fused alloy of tin and lead is allowed to freeze the thermometer becomes stationary at two suc cessive points, as shown in the following table, where x means the number of atomic weights of tin united with y of lead in the given case, and the temperatures are in centigrade degrees. First point (325) Second point (325) 1 3 280 187 1 240 187 3 1 187&quot; 187 4 1 1H7 187 12 1 210 187

(228&quot;) (228) We see that the first point varies with, while the second, within the range of the experiments, proved independent of, the proportion in which the two metals are united. The melting-point of many alloys lies below that of even the most fusible component, as illustrated in the following tables, where the numbers mean parts by weight. Tin and Lead (Rudberg). Per cent, of Tin. Per cent, of Lead. Melting-point. 100

228

100 325 74 20 194 f&amp;gt;3 37 186 63 47 196 30 04 241 1C 84 289 Name of Alloy. Tin. Lead. i Bismuth. Cadmium. Melting- point. Newton s 3 1 5

100 Rose s 3 8 8

95 1 1 2

93-7 Wood s 2 4 7 1 70 (Cadmium)

1 (320) All these alloys melt in boiling water. The electric conductivity of alloys qua alloys has been investi gated by Matthiesen. He confined himself to binary alloys derived from a certain set of elementary metals. The main results of his researches are given in ELECTRICITY, vol. viii. p. 51. For the practical electrician it is important to observe how very much the conductivity of copper is impaired by very minute admixtures even of metals that are good conductors, and also by non-metallic con tamination, especially with oxygen (present as Cu 2 0). Metallic Substances Produced by the Union of Metals witfi Small Proportions of Non-Metallic Elements. Hydrogen, as was shown by Graham, is capable of uniting with (always very large proportions of) certain metals, notably with palladium, into metal-like compounds. But those hydrogen alloys, being devoid of metallurgic interest, fall better under the heading PALLADIUM. Oxygen. Mercury and copper (perhaps also other metals) are capable of dissolving their own oxides with formation of alloys. Mercury, by doing so, becomes viscid and unfit for its ordinary applications. Copper, when pure to start with, suffers considerable deterioration in plasticity. But the presence of moderate proportions of cuprous oxide has been found to correct the evil influence of small contaminations by arsenic, antimony, lead, and other foreign metals. Most commercial coppers owe their good qualities to this compensating influence. Arsenic combines readily with all metals into true arsenides, which latter, in general, are soluble in the metal itself. The presence in a metal of even small proportions of arsenide generally leads to considerable deterioration in mechanical qualities. Phosphorus. The remark just made might be said to hold for phosphorus were it not for the existence of what is called &quot; phosphorus-bronze,&quot; an alloy of copper with phosphorus (i.e., its own phosphide), which possesses valu able properties. According to Abel, the most favourable effect is produced by from 1 to 1 per cent, of phosphorus. Such an alloy can be cast like ordinary bronze, but excels the latter in hardness, elasticity, toughness, and tensile strength. See PHOSPHORUS. Carbon. Most metals when in a molten state are capable of dissolving at least small proportions of carbon, which, in general, leads to a deterioration in metallicity, except in the case of iron, which by the addition of small percentages of carbon gains in elasticity and tensile strength with little loss of plasticity (see IRON). Silicon, so far as we know, behaves to metals pretty much like carbon, but our knowledge of facts is limited. What is known as &quot; cast iron &quot; is essentially an alloy of iron proper with 2 to 6 per cent, of carbon and more or less of silicon (see IRON). Alloys of copper and silicon were prepared by Deville in 1863. The alloy with 12 per cent, of silicon is white, hard, and brittle. When diluted down to 4 8 per cent., it assumes the colour and fusibility of bronze, but, unlike it, is tenacious and ductile like iron. Action of the More Ordinary Chemical Agente on Simple Metals. To avoid repetition, let us state beforehand that the metals to be referred to are always understood to be given in the compact (frozen) condition, and that, wherever a series of metals are enumerated as being similarly attacked, the degree of readiness in the action is (so far as our knowledge goes) indicated by the order in which the several members are named, the more readily changed metal always standing first. Water, at ordinary or slightly elevated temperatures, is decomposed more or less readily, with evolution of hydrogen gas and formation of a basic hydrate, by (1) potassium (formation of KHO), sodium (NaHO), lithium (LiOH), barium, strontium, calcium (BaO. 2 H 2, &amp;lt;fec.) ; (2) magnesium, zinc, manganese (MgOoH 2, d C.). In the case of group 1 the action is more or less violent, and the hydroxides formed are soluble in water and very