the crushing of the quartz in which gold was found, innumerable inventions in stamp mills, rollers, crushers, abraders, pulverisers and amalgamators have been invented; and so with roasters, and furnaces, and crucibles to melt the precious metal, separate the remaining impurities and convert it to use.

As to chemical methods for the precious metals, the process of lixiviation, or leaching, by which the ore is washed out by a solution of potash, or with dilute sulphuric acid, or boiling with concentrated sulphuric acid, is quite modern. About 1889 came out the great cyanide process, also known as the MacArthur-Forrest process (they being the first to obtain patents and introduce the invention), consisting of the use of cyanide potassium in solution, which dissolves the gold, and which is then precipitated by the employment of zinc. This process is best adapted to what are known as free milling or porous ores, where the gold is free and very fine and is attracted readily by mercury.

In 1807, Sir Humphry Davy discovered the metal potassium by subjecting moistened potash to the action of a powerful voltaic battery; the positive pole gave off oxygen and the metallic globules of pure potassium appeared at the negative pole. It is never found uncombined in nature. Now if potassium is heated in cyanogen gas (a gas procured by heating mercury) or obtained on a large scale by the decomposition of yellow prussiate of potash, a white crystalline body very soluble in water, and exceedingly poisonous, is obtained. When gold, for instance, obtained by pulverising the ore, or found free in sand, is treated to such a solution it is dissolved from its surrounding constituents and precipitated by the zinc, as before stated.

Chlorine is another metal discovered by Scheele in 1774, but not known as an elementary element until so established by Davy's investigations in 1810, when he gave it the name it now bears, from the Greek chloras, yellowish green. It is found abundantly in the mineral world in combination with common salt. Now it was found that chlorine is one of the most energetic of bodies, surpassing even oxygen under some circumstances, and that a chlorine solution will readily dissolve gold.

These, the cyanide and chlorination processes, have almost entirely superseded the old washing and amalgamating methods of treating free gold-and the cyanide seems to be now taking the lead.

Alloys. The art of fusing different metals to make new compounds, although always practised, has been greatly advanced by the discoverers and inventors of the century. As we have seen, amalgamating to extract gold and silver, and the making of bronze from tin and copper were very early followed. One of the most notable and useful of modern inventions or improvements of the kind was that of Isaac Babbitt of Boston in 1839, who in that year obtained patents for what ever since has been known as "babbitting." The great and undesirable friction produced by the rubbing of the ends of journals and shafts in their bearings of the same metal, cast or wrought iron, amounting to one-fifth of the amount of power exerted to turn them, had long been experienced. Lubricants of all kinds had been and are used; but Babbitt's invention was an anti-friction metal. It is composed of tin, antimony, and copper, and although the proportions and ingredients have since been varied, the whole art is still known as babbitting.

Other successful alloys have been made for gun metal, sheathing of ships, horseshoes, organ pipes, plough shares, roofing, eyelets, projectiles, faucets, and many and various articles of hardware, ornamental ware, and jewelry.

Valuable metals, such as were not always rare or scarce, but very hard to reduce, have been rendered far less in cost of production and more extensive in use by modern processes. Thus, aluminium, an abundant element in rocks and clay, discovered by the German chemist Wöhler, in 1827, a precious metal, so light, bright, and tough, non-oxidizing, harder than zinc, more sonorous than silver, malleable and ductile as iron, and more tenacious, has been brought to the front from an expensive and mere laboratory production to common and useful purposes in all the arts by the processes commencing in 1854 with that of St. Clair Deoville, of France, followed by those of H. Rose, Morin, Castner, Tissier, Hall, and others.

Electro-metallurgy, so far, has chiefly to do with the decomposition of metals by the electric current, and the production of very high temperatures for furnaces, by which the most refractory ores, metals, and other substances may be melted, and results produced not obtainable in any other way. By placing certain mixtures of carbon and sand, or of carbon and clay, between the terminals of a powerful current, a material resembling diamonds, but harder, has been produced. It has been named carbonundrum. The production of diamonds themselves is looked for. Steel wire is now tempered and annealed by electricity, as well as welding done, of which mention further on will be made.

Thus we have seen how the birth of ideas of for

mer generations has given rise in the present age to children of a larger growth. Arts have grown only as machinery for the accomplishment of their objects has developed, and machinery has waited on the development of the metals composing it. The civilisation of to-day would not have been possible if the successors of Tubal Cain had not been like him, instructors "of every artificer in brass and iron."

CHAPTER XV.

METAL WORKING.

WE referred in the last chapter to the fact that metal when it came from the melting and puddling furnace was formerly rolled into sheets; but, when the manufacturers and consumers got these sheets then came the severe, laborious work by hand of cutting, hammering, boring, shaping and fitting the parts for use and securing them in place.

It is one of the glories of this century that metalworking tools and machinery have been invented that take the metal from its inception, mould and adapt it to man's will in every situation with an infinite saving of time and labour, and with a perfection and uniformity of operation entirely impossible by hand.

Although the tools for boring holes in wood, such as the gimlet, auger, and the lathe to hold, turn and guide the article to be operated on by the tool, are common in some respects with those for drilling and turning metal, yet, the adaptation to use with metal constitutes a class of metal-working appliances distinct in themselves, and with some exceptions not interchangeable with wood-working utensils. The metal-working tools and machines forming the subject of this chapter are not those which from time immemorial have been used to pierce, hammer, cut, and shape metals, directed by the eye and hand of man,