478 CHREOTECHNICS. 



Vitrefactures ; Metallifactures ; Horology, and Musical instruments ; 

 and Cabinet and Carriage work ; with interspersed notices of minor 

 articles. 



1. Under the head of Vitrefactures, we include glass, pottery, 

 and porcelain ; though strictly speaking, the latter are vitrified only 

 on the surface, by glazing. Glass, is composed of sand, that is, silex 

 or silicic acid, melted with an alkali, usually potassa or soda, in the 

 furnace of a glass house. Bottle glass, is made of common sand 

 and potash ; and is colored green by the oxide of iron in the materials. 

 When melted, a portion of it will adhere to the end of a long iron 

 tube dipped in it, and on blowing into the tube, it swells out like a 

 soap bubble, and thus receives its shape. Crown glass, used for 

 windows, is made of purer sand and alkali ; with a little oxide of 

 manganese to render it quite colorless : and it is shaped by rapid 

 whirling on the end of a tube. Plate glass, is of similar composi- 

 tion ; and is cast in plates, on large tables. Flint glass, contains 

 not only pure sand and alkali, but a large portion of the oxide of 

 lead ; which renders it more brilliant, and softer to cut, or rather to 

 grind ; as for table glass. The cutting of gems, by the Lapidary, is 

 chiefly effected by rubbing them with fine, hard, powders. 



Pottery, or common earthen ware, is made like brick ; except that 

 the tempered clay is shaped by throwing, that is, placing it on a 

 wheel turning rapidly on a vertical axis, and moulding it with the 

 hands, or tools, into a rounded form. It is burnt in saggars, or 

 larger vessels, previously burnt, and which serve to protect it while 

 burning. It is often glazed, by throwing salt into the kiln ; the soda 

 of which converts its surface into a kind of glass : and, like glass, it 

 may be colored by metallic oxides. Stone ware, of a gray color, is 

 made of clay containing less or no iron ; and it is thoroughly burned. 

 White ware, including Wedgewood and Queen's ware, is made of 

 the finest white clay ; and in the former, a portion of flint is added, 

 by which it is partially vitrified throughout. China ware, and 

 porcelain, are made of feldspar, finely pulverized, and mixed with 

 kaolin, which is feldspar deprived of its potassa by decomposition. 

 The feldspar melts while burning, and enveloping the particles of 

 kaolin, gives the ware its translucency, It is burnt in saggars, like 

 pottery, forming what is called biscuit ; which is coated with paste 

 of feldspar, and then burnt anew, to glaze it. 



2. Under the head of Metallifactures, we include the manufac- 

 ture of hardware, brassware and jewelry : reserving, however, that 

 of watches, for the following section. By hardware, is usually 

 meant that made of iron or steel ; as kettles, and similar vessels, of 

 cast iron : but knives, forks, scissors, and the like, made of steel, 

 are collectively termed cutlery. The former class, are made of cast 

 iron, by the process of melting and founding: but the latter are 

 shaped from bars of steel, by forging or hammering, either on a plain 

 anvil, or on a block so shaped as to form a pattern. They are then 

 hardened, by plunging them, when red hot, into cool water or oil ; 

 and afterwards tempered, by heating them anew to about 500 Fah., 

 by which they are rendered less brittle. Lastly, they are polished, 



