Page:EB1911 - Volume 18.djvu/220

 {| class=_tablecolhdborder
 * rowspan=2|Name of Metal.||colspan=2|Relative Conductivities.
 * Electric.||Thermic.
 * Copper, commercial, No. 3 ||&numsp;·774&numsp; at 18·8° ||
 * Copper, commercial, No. 2 || ·721  at 22·6||
 * Copper, chemically pure, hard drawn&ensp;|| ·93 ||
 * Copper || ||| ·748
 * Gold, pure || ·552  at 21·8||| ·548
 * Gold, absolutely pure || ·73  at 19·0||
 * Brass|| ||| ·25
 * Tin, pure|| ·115  at 21·0 ||| ·154
 * Pianoforte Wire || ·144  at 20·4||
 * Iron rod|| ||| ·101
 * Steel|| ||| ·103
 * Lead, pure|| ·0777 at 17·3||| ·079
 * Platinum|| ·105  at 20·7||| ·094
 * German silver|| ·0767 at 18·7 ||| ·073
 * Bismuth|| ·0119 at 13·8||
 * Aluminium|| ·196  at 19·6||
 * Mercury || ·0163 at 22·8||
 * Silver, pure||1·000  at  0|||1·000
 * }
 * Pianoforte Wire || ·144  at 20·4||
 * Iron rod|| ||| ·101
 * Steel|| ||| ·103
 * Lead, pure|| ·0777 at 17·3||| ·079
 * Platinum|| ·105  at 20·7||| ·094
 * German silver|| ·0767 at 18·7 ||| ·073
 * Bismuth|| ·0119 at 13·8||
 * Aluminium|| ·196  at 19·6||
 * Mercury || ·0163 at 22·8||
 * Silver, pure||1·000  at  0|||1·000
 * }
 * Bismuth|| ·0119 at 13·8||
 * Aluminium|| ·196  at 19·6||
 * Mercury || ·0163 at 22·8||
 * Silver, pure||1·000  at  0|||1·000
 * }
 * Mercury || ·0163 at 22·8||
 * Silver, pure||1·000  at  0|||1·000
 * }
 * }

Chemical Changes.—Metals may unite chemically both with metals and with non-metals. The compounds formed in the first case, which may be either definite chemical compounds or solid solutions, are discussed under ; in this place only combinations with non-metals are discussed, it being premised that the free metal takes part in the reaction.

Metallic Substances Produced by the Union of Metals with Small Proportions of Non-Metallic Elements.

Hydrogen, as was shown by Graham, is capable of uniting with or being occluded by certain metals, notably with (q.v.), into metal-like compounds.

Oxygen.—Mercury and copper and some other metals are capable of dissolving their own oxides. 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. Commercial coppers sometimes 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 “phosphorus-bronze,” an alloy of copper with phosphorus (i.e. its own phosphide), which possesses valuable properties. According to Abel, the most favourable effect is produced by from 1 to 1%, of phosphorus. Such an alloy can be cast like ordinary bronze, but excels the latter in hardness, elasticity, toughness and tensile stren

Carbon.—Most metals when molten 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 ).

Silicon, so far as we know, behaves to metals pretty much like carbon, but our knowledge of facts is limited. What is known as cast iron is essentially an alloy of iron proper with 2 to 6% of carbon and more or less of silicon (see ). Alloys of copper and silicon were prepared by Deville in 1863. The alloy with 12% of silicon is white, hard and brittle. When diluted down to 4·8%, it assumes the colour and fusibility of bronze, but, unlike it, is tenacious and ductile like iron.

Action of the More Ordinary Chemical Agents on Simple Metals.

The metals to be referred to are always understood to be given in the compact (frozen) condition, and that, wherever metals are enumerated as being similarly attacked, the degree of readiness in the action is 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 (BaH2O2, &c.); (2) magnesium, zinc, manganese (MgO2H2, &c.).

In the case of group 1 the action is more or less violent, and the hydroxides formed are soluble in water and very-strongly basic; metals of group 2 are only slowly attacked, with formation of relatively feebly basic and less soluble hydroxides. Disregarding the rarer elements, the metals not named so far may be said to be proof against the action of pure water in the absence of free oxygen (air).

By the joint action of water and air, thallium, lead, bismuth are oxidized, with formation of more or less sparingly soluble hydroxides (ThHO, PbH2O2, BiH3O3), which, in the presence of carbonic acid, pass into still less soluble basic carbonates. Iron, when exposed to moisture and air, “rusts”; but this process never takes place in the absence of air, and it is questionable whether it ever sets in in the absence of carbonic acid (see ).

Copper, in the present connexion, is intermediate between iron and the following group of metals.

Mercury, if pure, and all the “noble” metals (silver, gold, platinum and platinum-metals), are absolutely proof against water even in the presence of oxygen and carbonic acid.

The metals grouped together above, under 1 and 2, act on steam pretty much as they do on liquid water. Of the rest, the following are readily oxidized by steam at a red heat, with formation of hydrogen gas—zinc, iron, cadmium, cobalt, nickel, tin. Bismuth is similarly attacked, but slowly, at a white heat. Aluminium is barely affected even at a white heat, if it is pure; the ordinary impure metal is liable to be very readily oxidized.

Aqueous Sulphuric or Hydrochloric Acid readily dissolves groups 1 and 2, with evolution of hydrogen and formation of chlorides or sulphates. The same holds for the following group (A): [manganese, zinc, magnesium] iron, aluminium, cobalt, nickel, cadmium. Tin dissolves readily in strong hot hydrochloric acid as SnCl2; aqueous sulphuric acid does not act on it appreciably in the cold; at 150° it attacks it more or less quickly, according to the strength of the acid, with evolution of sulphuretted hydrogen or, when the acid is stronger, of sulphurous acid gas and deposition of sulphur (Calvert and Johnson). A group (B), comprising copper, is, substantially, attacked only in the presence of oxygen or air. Lead, in sufficiently dilute acid, or in stronger acid if not too hot, remains unchanged. A group (C) may be formed of mercury, silver, gold and platinum, which) are not touched by either aqueous acid in any circumstances.

Hot (concentrated) sulphuric acid does not attack gold, platinum and platinum-metals generally; all other metals (including silver) are converted into sulphates, with evolution of sulphur dioxide. In the case of iron, ferric sulphate, Fe2(SO4)3, is produced; tin yields a somewhat indefinite sulphate of its oxide SnO2.

Nitric Acid (Aqueous)—Gold, platinum, iridium and rhodium only are proof against the action of this powerful oxidizer. Tin and antimony (also arsenic) are converted by it (ultimately) into hydrates of their highest oxides SnO2, Sb2O5 (As2O5)—the oxides of tin and antimony being insoluble in water and in the acid itself. All other metals, including palladium, are dissolved as nitrates, the oxidizing part of the reagent being generally reduced to oxides of nitrogen. Iron, zinc, cadmium, also tin under certain conditions, reduce the dilute acid, partially at least, to nitrous oxide, N2O, or ammonium nitrate, NH4NO3.

Aqua Regia, a mixture of nitric and hydrochloric acids, converts all metals (even gold, the “king of metals,” whence the name) into chlorides, except only rhodium, iridium and ruthenium, which, when pure, are not attacked.

Caustic Alkalis.—Of metals not decomposing liquid pure water, only a few dissolve in aqueous caustic potash or soda, with evolution of hydrogen. The most important of these are aluminium and zinc, which are converted into aluminate, Al(OK, Na)3, and zincate, Zn(OK, Na)2, respectively. But of the rest the majority, when treated with boiling sufficiently strong alkali, are attacked at (least superficially; of ordinary metals only gold, platinum, and silver are perfectly proof against the reagents under consideration, and these accordingly are used preferably for the construction of vessels intended for analytical) operations involving the use of aqueous caustic alkalis. For commercial purposes iron is universally employed and works well; but it is not available analytically, because a superficial oxidation of the empty part of the vessel (by the water and air) cannot be prevented. Basins made of pure malleable nickel are free from this drawback; they work as well as platinum, and rather better than silver ones do. There is hardly a single metal which holds out against the alkalis themselves when in the state of fiery fusion; even platinum is most violently attacked. In chemical laboratories fusions with caustic alkalis are always effected in vessels made of gold or silver, these metals holding out fairly well even in the presence of air. Gold is the better of the two. Iron, which stands so well against aqueous alkalis, is most violently attacked by the fused reagents. Yet tons of caustic soda are fused daily in chemical works in iron pots without thereby suffering contamination, which seems to show that (clean) iron, like gold and silver, is attacked only by the joint action of fused alkali and air, the influence of the latter being of course minimized in large-scale operations.

Oxygen or Air.—The noble metals (from silver upwards) do not combine directly with oxygen given as oxygen gas (O2), although, like silver, they may absorb this gas largely when in the fused condition, and may not be proof against ozone, O3. Mercury, within