Refrigeration is at present its most natural and obvious use, and it is claimed that eleven gallons of the material when gradually expanded has the refrigerating power of one ton of ice. Its use of course for all purposes for which cold can be used is thus assured. It is also to be used as a motor in the running of various kinds of engines. It is to be used as a great alleviator of human suffering in lowering and regulating the temperature of hospitals in hot weather, and in surgical operations as a substitute for anæsthetics and cauterising agents. It was one of the marvellous attractions at the great Paris Exposition of 1900. Lighting is closely allied to the various subjects herein considered, but consideration of the various modes and kinds of lamps for lighting will be reserved for the Chapter on Furniture for Houses, etc. CHAPTER XIV. METALLURGY. “Nigh on the plain, in many cells prepared, That underneath had veins of liquid fire Sluiced from the lake, a second multitude With wondrous art founded the massy ore; Severing each kind, and scumm’d the bullion dross; A third as soon had formed within the ground A various mould, and from the boiling cells By strange conveyance fill’d each hollow nook; As in an organ, from one blast of wind, To many a row of pipes the sound board breathes.” --_Paradise Lost._ Ever since those perished races of men who left no other record but that engraven in rude emblems on the rocks, or no other signs of their existence but in the broken tools found buried deep among the solid leaves of the crusted earth, ever since Tubal Cain became “an instructor of every artificer in brass and iron,” the art of smelting has been known. The stone age flourished with implements furnished ready-made by nature, or needing little shaping for their use, but the ages of metal which followed required the aid of fire directed by the hand of man to provide the tool of iron or bronze. The Greeks claimed that the discovery of iron was theirs, and was made at the burning of a forest on the mountains of Ida in Crete, about 1500 B. C., when the ore contained in the rocks or soil on which the forest stood was melted, cleansed of its impurities, and then collected and hammered. Archeologists have deprived the Greeks of this gift, and carried back its origin to remoter ages and localities.