CHAPTER I INTRODUCTION § 1. That metals are capable of uniting with each other to form a series of bodies, having more or less the properties of their constituents, has long been known, and probably this knowledge has been usefully applied from remote antiquity. The ancients were acquainted with seven metals, viz. gold, silver, mercury, copper, iron, tin, and lead. They knew and employed various compounds of antimony, arsenic, and zinc; although we have no evidence that these metals were known to them in the metallic state. Gold and silver, which occur in nature in the metallic state, were probably the first metals with which man became acquainted, and as other metals were discovered, especially copper, attempts would doubtless be made to alloy the base metals with gold, in consequence of the comparative rarity of the latter. Copper is also occasionally found "native," and to persons accustomed to melt the precious metals, there would be no difficulty in melting copper and alloying it with gold and silver. The Latin word aes in ancient writings sometimes signifies copper, and sometimes brass, so that the two metals were occasionally confounded together. Pliny says, "that an ore of aes, termed chalcitis, occurs in Cyprus, where aes was first discovered." Here aes obviously means copper. In another place he says that aes is obtained from a mineral called cadmia. Now cadmia is the ore known at the B present time as calamine, which is chiefly a carbonate of zinc. This substance, when mixed with charcoal, and strongly heated for some time in a closed crucible in admixture with metallic copper, or with an oxide of copper, forms brass. The proper name for brass was aurichalcum, or golden copper, and it may be inferred that ores of copper and zinc were sometimes smelted together forming brass, as the metal zinc in the free state was probably unknown till the sixteenth century. Pliny describes four different varieties of what was known as Corinthian copper. 1. White. It resembles silver in lustre and contains an excess of that metal. 2. Red. In this kind there is an excess of gold. 3. In this kind, gold, silver, and copper are mixed in equal proportions. 4. This variety was termed hepatizon, from its having a liver colour, which gives it its value. Copper was used by the ancients for many of the purposes to which it is put by the moderns. The alloys of copper with tin were used in various proportions, thus: bronze for statues was composed of 100 parts copper and 12 parts tin. Another mixture was 100 parts copper, 10 parts lead, and 5 parts tin. Culinary pots were made of an alloy of 100 parts copper and 3 to 4 parts tin. The arms of the ancients were often made of bronze, which was rendered hard by heating and allowing to cool slowly. It was Tin was in common use in the time of Moses. doubtless the Phoenicians who supplied the Egyptians with this metal, which the former obtained from the Scilly islands and Cornwall. Cassiteros, or tin, is mentioned by Homer. In the time of Pliny, tin was used for coating the interior of copper and brass vessels. Mercury was used by the Romans for alloying with gold and silver to form amalgams, which were used for gilding and plating, as at the present time, by laying the amalgam on the base metals, and subsequently volatilising the mercury by heat, leaving a thin coating of the precious metal on the article. Lead was well known to the ancient Egyptians, as well as to the Romans, by whom it was termed plumbum nigrum. Large quantities of lead were obtained from Spain and Britain. Sheet lead and lead piping were used for similar purposes to those for which they are employed at the present time. A mixture of lead and tin was also used as a solder. Iron was known in very early times, but in comparatively small quantities, being obtained from meteoric stones, or easily reducible oxides. Moses speaks of iron being used for swords, knives, axes, etc., which seems to imply that steel was known at that early period. Homer represents warriors as armed with bronze swords, and never as using iron weapons. Achilles proposes a ball of iron as a valuable prize to be contended for in the games, which shows its scarcity at that period. That the Romans were acquainted with steel, as well as with the method of hardening and tempering it, we have abundant evidence. The steel was probably manufactured direct from iron ore. Steel may be considered as an alloy of iron and carbon, into which manganese occasionally enters in small proportion. Thus the ancients knew the six malleable metals and their alloys above referred to, but they have left us scant information respecting the methods of extracting them from the ores. It is probable that only those ores of a simple character, or those readily acted upon by reducing agents, were employed, unless the appliances at their disposal and their general chemical knowledge were superior to what known facts warrant us in believing. In the eighteenth century the investigation of the nature of alloys began to receive systematic scientific attention. Thus Reaumur, an indefatigable French chemist, concluded that steel was iron impregnated with sulphurous and saline matters. The word "sulphurous" as used at that time is nearly synonymous with the present term “combustible." At the end of that century, Berthollet concluded from his own experiments and those of Reaumur that steel was a compound of iron and carbon. Reaumur also explained the principle of the method of tinning iron plates. Gellert in his Metallurgic Chemistry endeavours to point out the analogy between alloys and solutions, and gives a table showing the relative solubilities of metals in each other, such as copper in silver. He further clearly showed that with regard to the solution of metals in a triple alloy, he understood the possibility of the division of a metal between two metals acting as solvents. Musschenbroek in the early part of the eighteenth century made some experiments on the tensile strength of metals and alloys. He writes of the "absolute cohesion by which a body resists fracture when acted on by forcedrawing according to its length." Duhamel in 1792 writes of the necessity for making exact experiments upon alloys, with metals which possess a high degree of purity, the union being effected in closed vessels. In the early part of the nineteenth century the researches on alloys became more numerous, and the interest excited in them has continued to grow to the present day. NATURE OF METALS § 2. The term "metal" indicates a certain number of the chemical elements which have well-defined characters in common, such as metallic lustre, conductivity, and high specific gravity. When separated from their compounds by electrolytic action they appear at the negative electrode, and hence belong to the class of electro-positive bodies. These properties are by no means equally developed in all cases; in some instances one or more of these characteristics may be absent. On the other hand, there are substances not metallic in character in which some of these properties are strongly displayed. Thus, graphite has a metallic lustre, gas-carbon and silicon are conductors of heat and electricity, and the alkali metals are lighter than water. In fact, while there are elements having strongly marked characteristics, which may unhesitatingly be classed as metallic, there are others, such as arsenic, which have properties either metallic or non-metallic |