FOUNDING; FOUNDRY 479 



The whole mass is now to be thoroughly dried by the continuance of the fire, the 

 draught of which is supported by a small vent left in the upper part of the new dome ; 

 and when all is properly dry, the two iron platforms are adjusted to each other by pin 

 points, and p q is lifted off, taking care to keep it in a horizontal position. Upon this 

 platform are removed the last brick dome, and the layer of loam which had been 

 applied next to it; the latter of which represents exactly by its inside the mould of 

 the surface e' f, that is, of the outside of the pan. The crust contained between ef 

 and d f is broken away, an operation easily done without injury to the surface e f, 

 which represents exactly the inner surface of the pan ; or only to the shoulder m, 

 corresponding to the edge of the vessel. The top aperture through which the upright 

 shaft passed must be now closed ; only the one is kept open in the portion of the 

 mould lifted off upon p q ; because through this opening the melted metal is to be 

 poured in the process of casting. The two platforms being replaced above each other 

 exactly, by means of the adjusting pin-points, the mould is completely formed, and 

 ready for the reception of the metal. 



When the object to be moulded presents more complicated forms than the one now 

 chosen for the sake of illustration, it is always by analogous processes that the work- 

 man constructs his loam moulds, but his sagacity must hit upon modes of executing 

 many things which at first sight appear to be scarcely possible. Thus, when the 

 forms of the interior and exterior do not permit the mould to be separated in two 

 pieces, it is divided into several, which are nicely fitted with adjusting pins. More 

 than two cast-iron rings or platforms are sometimes necessary. When ovals or 

 angular surfaces must be traced instead of those of revolution, no upright shaft is used, 

 but wooden or cast-iron guides made on purpose, along which the pattern cut-out 



998 



999 



board is slid according to the drawing of the piece. ^ Iron wires and claws are often 

 interspersed through the brick-work to give it cohesion. The core, kernel, or inner 

 mould of a hollow casting is frequently fitted in when the outer shell is moulded. 

 The case of a gas-light retort, fig. 998, will illustrate this matter. The core of the 

 retort ought to have the form e e e e, and be very solid, since it cannot be fixed in the 

 outer mould for the casting, except in the part standing out of the retort towards m m. 

 It must be modelled in loam, upon a piece of cast iron called a lantern, made expressly 

 for this purpose. The lantern is a cylinder or a truncated hollow cone of cast iron, 

 about half an inch thick; and differently shaped for every different core. The 

 surface is perforated with holes of about half an inch in diameter. It is mounted by 

 means of iron cross-bars, upon an iron axis, which traverses it in the direction of its 

 length. Fig. 999, represents a horizontal section through the axis of the core ; g h is 

 the axis of the lantern, figured itself at i k k i', o i i o is a kind of disc or dish, per- 

 pendicular to the axis, open at i i, forming one piece with the lantern, whose circum- 

 ference o o presents a curve similar to the section of the core, made at right angles to 

 its axis. We shall see presently the two uses for which this dish is intended. The 

 axis g h is laid upon two gudgeons, and handles are placed at each of its extremities, 

 to facilitate the operation in making the core. Upon the whole surface of the lantern, 

 from the point h to the collet formed by the dish, a hay cord as thick as the finger is 

 wound. Even two or more coils may be applied, as occasion requires, over which 

 loam is spread to the exact form of the core, by applying with a hand a board, against 

 the dish o o, with its edge cut out to the desired shape ; as also against another dish, 

 adjusted at the time towards k ; while by means of the handles a rotatory movement 

 is given to the whole apparatus. 



The hay interposed between the lantern and the loam, which represents the crust of 

 the core, aids the adhesion of the clay with the cast iron of the lantern, and gives passage 

 to the holes in its surface, for the air to escape through in the casting. 



When the core is finished, and has been put into the drying stove, the axis g k is 

 taken out, then the small opening which it leaves at the point h, is plugged with clay, 

 This is done by supporting the core by the edges of the dish, in a vertical position. It 

 is now ready to be introduced into the hollow mould of the piece. 



