348 Sloan's Architectural Review and Builders' Ji ournai [Xov., a thiii layer of moisture, which rapidly evaporates, abstracting heat from the vessel, and from the remainder of the contained water, and reducing the tem- perature of the latter several degrees below that of the surrounding atmo- sphere. The porosity, and, conse- quently, the cooling effect, is greatly increased by mixing with the raw clay, organic matter, finely subdivided, which, in the baking process, being completely destroyed, leaves minute pores ; or, salt being mixed, is dissolved out, by water, after the baking of the vessel. In the mixed Spanish dialect of South America, these vessels are called canaria, though the knowledge of them and of their properties, is not the spontaneous growth of the exigencies of the climate, but was transmitted from the European ancestry of the people. These, them- selves, derived it from the Moors, the vessels having been manufactured, from the remotest times, in warm countries. The Spanish name, alcarazza, is a cor- ruption of the Moorish Al-Earazah. In upper Egypt, where such quantities are manufactured, and at such cheap rates, that one is scarcely used the second time, they are generally made very thin, and are perfumed by inverting them over a piece of gum mastich placed on a burn- ing coal, itself a very ancient custom, if we are to credit Athenseus, according to whom, vases made at Coptos, and per- fumed by mastich and myrrh, had the property of depriving wine of its intox- icating effects. In the interesting work of Marryat, from which we have fre- quently quoted, and to which we are indebted for many of our historical facts, is described the manner of transporta- tion of these vessels, from Kenneh, in upper Egypt, to Cairo, by forming them into rafts, and sending the fragile float, with a single conductor or steersman, down the Nile — a manner of convej'ance certainly cheap, but precarious, yet an- tique, and recommending itself, on this score, to the strong " conservative ele- ment" of the Egyptian population — for Juvenal tells us that the Egyptian " boats were made of earthenware, and painted." Of Water Conduits, or Tubes, the best are made by kneading together, into the form of cakes, a mixture of good plastic clay, with an impurer variety containing considerable sand, mica, and oxide of iron, and then forcing the mix- ture, through hollow cast-iron cylinders, into the moulds, by means of a hydro- static press. After thus giving them their desired shape and size, they are dried in a baking-kiln ; and will then, it is stated, resist a pressure of nearly one thousand pounds to the square inch — a result impossible to bring about by any of the ordinary means, without the use of the press. Drain Tiles, for Agricultural Pur- poses, are constructed on the same prin- ciple of forcing the clay, from cylinders, through the proper die-plates, attached to their lower extremities. Roofing-Tiles were formerly moulded on a flat board, around which was nailed a rim of the desired thickness of the tile ; the arched or curved form, if thought advisable, being given after- wards, by bending the flat tile around a block of wood. An improvement is also effected in the production of these, by the use of the press, as above, the product being much denser, and less liable to destruction from frost. Their durability in this latter particular is also greathy enhanced by glazing : the ordinaiy potter's glaze brought to the desired color by metallic oxides being- used. Wonderful alchemists are the potters and glass makers! A few particles of sand, or a little clay, assuming, in their hands, so many forms of use and beauty, — transmuting the weather-worn, current-drifted and powdered rock into shapes to minister to man's comforts or pleasures. . We may trace much of the histoiy of the progress of the human race in the dis- tinctive character their hands have im-
