(Water - 1).
The physical properties of the metals are largely dependent on their purity and molecular condition, and on temperature. Hammered, rolled, or drawn metal generally has a higher specific gravity than cast metal. The state of molecular tension often induced by mechanical working, especially when cold, is resolved by annealing, i. e., heating and slow cooling. Must of the metals are more malleable and ductile at high temperatures. Commercial zinc is only malleable between 100° and 150° C; at 200° it is so brittle that it can be pulverized. The conductivity for electricity is greatly diminished at high temperatures, and also by the presence of impurities in the metal. The addition of a small amount of a foreign substance often makes a metal harder, more rigid, and less susceptible of elongation. This is notably the case with iron, which when pure oft and stretches considerably under strain before breaking, while steel, which is iron with a small amount of carbon, maybe rigid and brittle. If reference be had to the original area of section, the rigid metal will show the greatest strength under a gradually applied tensile strain; but if to the fractured area, the purer metal is the strongest. The tenacity of metals generally decreases as the temperature is named.
The fusing points of the more refractory metals given in the above tables are approximate only, since trustworthy methods for determining high temperatures are wanting. The metals vary greatly in hardness. The alkaline metals are as soft as wax, while some, as chromium, will scratch glass. It is not improbable that extreme hardness in metals is produced by the presence of some foreign body, and is not inherent in the metal itself. Most of the metals are capable of assuming a distinctly crystalline form, generally belonging to the regular or isometric system. Some, as antimony and arsenic, crystallize in rhombo-hedrons. A few of the metals occur native; these are gold, platinum, palladium, iridium, and rhodium, which are almost exclusively found in the metallic state, and silver, copper, mercury, bismuth, arsenic, and antimony. Generally, however, the metals occur mineralized in combination with oxygen or sulphur. The specific heats of the metals, as will be noticed in the above tables, are inversely as their atomic weights, or, in other words, the specific heats of the atoms of the metals are equal. - Chemically, the metals present very varied characters.
As a class they are distinguished by the formation of compounds with oxygen which have basic characters, while the non-metals as a class form oxides which have acid characters. These two classes of oxides are capable of combining to form salts. While the oxides of the non-metals never form bases, the higher oxides of many of the metals have distinctly acid properties, and indeed a few of the metals form only acid oxides. The most stable compounds of tellurium, arsenic, antimony, tungsten, titanium, molybdenum, and vanadium with oxygen are acid in character and capable of combining with basic oxides. Those metals which seem to hold a position intermediate between the two classes have been termed half metals or metalloids. The latter term, as now generally used, includes all the non-metallic elements, viz.: hydrogen, oxygen, bromine, chlorine, iodine, fluorine, boron, nitrogen, phosphorus, selenium, silicon, sulphur, and carbon. Tellurium is closely related to sulphur and selenium, and is often classed with the metalloids; but its metallic appearance, and the analogy which its compounds bear to those of antimony, render its association with the metals equally appropriate.
Hydrogen, although a gas and the lightest body known, resembles the metals in its chemical properties, and is capable of replacing them in combination. The formation of salts is regarded in modern chemistry as the replacement of hydrogen in the acid by a metal. - The metals are variously classified. A natural grouping, and one in common use, is: 1, metals of the alkalies; 2, metals of the alkaline earths; 3, metals of the earths proper; 4, oxidable metals proper, whose oxides form powerful bases; 5, oxidable metals, whose oxides form weak bases or acids; 6, metals proper, whose oxides are reduced by heat, called noble metals. The strength of affinity of the different metals for oxygen is the basis of a classification formerly much used. It is embodied in part in the electro-chemical series of Berzelius, which played an important part in the development of chemical science. The alkaline metals oxidize rapidly in the air, and decompose water at ordinary temperatures; others, as iron and zinc, do not oxidize in pure dry air, and decompose water only at a red heat, or in contact with an acid; and others, as the noble metals, do not decompose water at any temperature. The electrical relations of the metals correspond in general to their affinity for oxygen.
Thus, the alkaline metals are the most electro-positive, and the noble metals the most electro-negative. The metals likewise fall into groups in which the individual members can replace one another in compounds without change of crystalline form; they are then said to be isomorphous. As examples may be cited magnesium, calcium, manganese, iron, zinc, copper, and aluminum; barium, strontium, and lead; sodium, silver, thallium, gold, and potassium; arsenic, antimony, and bismuth; tin, titanium, tungsten, and molybdenum; platinum, iridium, and osmium. The atomicity of the elements, or their combining values, forms the basis of classification for study in modern chemistry. Metals are thus divided into monads (or those replaceable by or equivalent to one atom of a monogenic element, as hydrogen or chlorine), dyads, triads, tetrads, pentads, and hexads, as follows: monads - lithium, sodium, potassium, rubidium, calcium, silver; dyads - calcium, strontium, barium, glucinum, yttrium, lanthanum, didymium, erbium, thorium, magnesium, zinc, cadmium, copper, mercury; triads - gold, thallium; tetrads - titanium, tin, aluminum, zirconium, rhodium, ruthenium, palladium, platinum, iridium, osmium, lead, manganese, iron, cobalt, nickel, cerium, indium, uranium; pentads - vanadium, arsenic, antimony, bismuth, niobium, tantalum; hexads - chromium, molybdenum, tungsten.
A few of the metals possess more than one atomicity, and appear in different compounds with different atomic values. The combinations of the metals with the non-metallic elements may be divided into two classes, those with chlorine, iodine, bromine, and fluorine, and those with oxygen, sulphur, selenium, and tellurium. The former class are saline compounds, while the latter are generally basic, exceptionally acid, as before mentioned. Formerly the distinction was generally observed between haloid and oxygen salts, the former being the combination of a metal with a haloid body, as chloride of sodium, and the latter a combination of a basic oxide with an oxy-acid, as sulphate of soda. In the modern chemistry both characters of salts are regarded as the replacements of hydrogen in the acid by a metal. The combinations of the metals among themselves are known as alloys, or, in case of mercury, as amalgams. (See Alloy, and Amalgam).