STEREOTYPE PRINTING 911 



the 9-inch arch of the furnace is reduced to the thickness of from 1 to 2 inches. It is 

 evident that silica is, chemically speaking, an objectionable material to be used in the 

 construction of these furnaces, because it prevents the formation of basic slags, and 

 that a furnace constructed of pure alumina or lime would be preferable. M. Le 

 Chatelier suggested, some years ago, the use of Bauxite (from Beaux in France, where 

 it was first discovered), a mineral consisting chiefly of alumina, for making the furnace- 

 beds, but Dr. Siemens was not able to succeed with this, owing to the great contraction 

 of the mass when intensely heated, and non-cohesion with the same material introduced 

 for the purpose of repair. In attempting to construct the sides and roof of the furnace 

 of Bauxite bricks, these were not found to be equal in heat-resisting power to silica- 

 bricks, which latter are indeed unobjectionable, except when raw ore and limestone 

 are used. See BATJXITE. 



STEEIi, HARDENING- OF. Steel may be hardened by plunging it into cold 

 water. Prussiate of potash and other salts are used for producing especval degrees of 

 hardness. See TEMPERING OP STEEL. 



STEMPIiES. A mining term. Strong pieces of timber, driven betwixt the 

 sides of a vein, at short distances apart, to support the walls. 



STEREOCHROME. A name given to a process of stereotyping, the printiug 

 of which is effected in colours. It is a term also used for the art of painting, with 

 silica fluids for mixing the colours. 



STEREOSCOPE (from Gr. <rrepf6s, stereos, 'solid,' and axo-nt'tv, sJcopein, 'to see'). 

 An instrument invented by Professor Wheatstone, and modified by Sir David Brewster, 

 by means of which two images of the same object, depicted on paper, as those images 

 would be depicted iipon the retina of each eye ^are resolved into an apparent solid of 

 three dimensions. The reflecting stereoscope of Professor Wheatstone was constructed 

 by means of two mirrors, set at right angles to each other, so that while the right eye 

 observed a reflected image of a picture placed on the right-hand side of the instrument, 

 the left eye saw a reflected image of that on the left, and, as a result, saw not two 

 plane pictures, but one solid image. The refracting stereoscope, which is generally 

 used, consists of two semi-lenses. This is a lens which is divided in the middle, and 

 the two halves, with the edges towards each other, placed in a frame, at a distance 

 from each other corresponding with the distances of the eyes apart. For the best 

 result, two pictures are obtained by photography, as nearly as possible of the same 

 character as the pictures impressed respectively upon the retina of each eye. See 

 Hunt's ' Manual of Photography.' 



STEREOTYPE PRINTING signifies printing by fixed types or by a cast typo- 

 graphic plate. This plate was formerly always, and is still sometimes, made as fol- 

 lows : The form, composed in ordinary types, and containing, one, two, three, or more 

 pages, inversely as the size of a book, being laid flat upon a slab, with the letters 

 looking upwards, the faces of the types are brushed over with oil, or, preferably, with 

 plumbago (black lead). A heavy brass rectangular frame of three sides, with bevelled 

 borders adapted exactly to the size of the pages, is then laid down upon the chase, 1 

 to circumscribe three sides of its typography ; but the fourth side, which is one end 

 of the rectangle, is formed by placing near the types, and over the hollows of the 

 chase, a single brass bar, having the same inwards-sloping bevel as the other three 

 sides. The complete frame resembles that of a picture, and serves to define the area 

 and thickness of the cast, which is made by pouring the pap of Paris-plaster into its 

 interior space up to a given line on its edges. The plaster-mould, which soon sets, 

 or becomes concrete, is lifted gently off the types, and immediately placed upright on 

 its edge in one of the cells of a sheet-iron rack mounted within the cast-iron oven. 

 The moulds are here exposed to air heated to fully 400 Fahr., and become perfectly 

 dry in the course of two hours. As they are now friable and porous, they require to 

 be delicately handled. Each mould, containing generally two pages octavo, is laid, with 

 the impression downwards, upon a flat cast-iron plate, called the floating-plate ; this 

 plate being itself laid on the bottom of the dipping-pan, which is a cast-iron square 

 tray, with its iipright edges sloping outwards. A cast-iron lid is applied to the dip- 

 ping-pan and secured in its place by a screw. The pan having been heated to 400 

 in a cell of the oven, under the mould-rack, previous to receiving the hot mould, is 

 ready to be plunged into the bath of melted alloy contained in an iron pot placed over 

 a furnace, and it is dipped with a slight deviation from the horizontal plane, iu order 

 to facilitate the escape of the air. As there is a minute space between the back or 

 top surface of the mould and the lid of the dipping-pan, the liquid metal on entering 

 into the pan through the orifices in its corners, floats up the plaster along with the 

 iron plate on which it had been laid, thence called the floating-plate, whereby it flows 

 freely into every lino of the mould, through notches cut in its edge, and forms a 



1 Chase (chassis, Pr., ' frame '), and quoin (coin, Fr., ' wedge '), are terms which show that the art 

 of printing is indebted to our French neighbours for many of its improvements. 



