474 FOUNDING; FOUNDRY 



sphere is pushed through the plate as before, and sand filled in, with great rapidity 

 and accuracy. 



The sand cores for filling up that part of the shell which is to bo hollow are also 

 carefully and quickly made at Woolwich. The halves of the core-mould, open and 

 shut with a lever, so that the bad plan of striking the core-mould is avoided as com- 

 pletely as the bad plan of striking the pattern is in the process of moulding shot and 

 shell. 



Theory of Casting. Before leaving the subject of the use of sand-moulds, we may 

 remark that iron and brass castings with a perfect surface can only be produced when 

 the mould is well dried and heated, so as to drive out any moisture from the apertures 

 between the grains of sand. By this means channels are opened for the rapid escape 

 of the heated air and gas expelled by the entrance of the fluid metal into the mould, 

 and the surface of the metal is not cooled by its contact with damp or cold sand. 

 It is also well to mix charcoal-dust, or coke-dust, with the sand ; and for fine castings 

 to cover the surface of the sand with a coating of charcoal-dust. The object of this 

 proceeding is to reduce the oxide which may be present in the metal. This operation 

 of reducing the oxide of a metal instantaneously is performed with the greatest cer- 

 tainty by this simple means, invented, probably, by the earliest metallurgists. By 

 incorporating a quantity of charcoal- or coke-dust with the sand, or facing the sand 

 with carbonaceous matter, any oxide of the metal which may be floating amongst 

 the pure metal is at once reduced. Sand (being a non-conductor) docs not abstract 

 the heat from the fluid metal rapidly, and, therefore, solidification of the metal takes 

 place comparatively regularly and equally throughout the mass ; when one part of the 

 casting solidifies before the adjoining part, flaws often occur, and to avoid these the 

 skill of the practical founder is necessary in arranging for the entrance of the metal 

 at the proper point, and for the exit of the air. 



We next proceed to the third class of improvements in moulding, that of the exten- 

 sion of the application of metallic moulds. 



Metal Moulds. The practice of casting bronze weapons in moulds made of bronze 

 (blackened over on their surface to prevent the fluid metal uniting with the mould) 

 appears to have been a very general one among the ancients. 



Some moulds of this description have been discovered amongst the prehistoric 

 remains disinterred in different parts of Europe. 



The facility for the escape of the heated air and gases from the sand-moulds into 

 which liquid metal is poured, is so much greater than that from moulds of metal, that 

 at the present time neither brass nor iron is poured into metallic moulds, except when 

 a particular purpose is to be attained, viz., that of chilling the surface of the iron and 

 making it as hard as steel. Iron cannot be chilled or hardened in a sand-mould. 



Chilled Iron. This process of casting in metal moulds was once supposed to be a 

 modern invention ; but it now appears, from the metal moulds discovered among the 

 remains of the Celtic race throughout Europe, that the bronze weapons of the people 

 who preceded the Romans were generally cast in metallic moulds, and not in sand. 

 Chilled castings have been brought to great perfection by Messrs. Ransome, of Ipswich. 

 Their chilled ploughshares and chilled railway chairs are cast in moulds of such a con- 

 struction that the melted iron comes in contact with iron in those parts of the moulds 

 where it is wanted to be chilled. A section of the casting shows the effect of chilling. 



Zinc. In casting zinc (a cheap and abundant metal), which fuses at a low tempera- 

 ture, metallic moulds may be most advantageously used. It is, however, necessary to 

 heat the iron or brass mould nearly to the temperature of molting zinc, in order that 

 the rapid abstraction of heat from the fluid metal may be prevented. The prepa- 

 ration of metal moulds, and the casting soft metal in them is now an extensive and 

 important industry on the Continent, for ornamental zinc castings have suddenly 

 come into extensive use in consequence of the discovery of the elcctrotyping process. 

 When covered with a thin coating of brass or copper by a galvanic battery, zinc may 

 be bronzed so as to present almost the exact external appearances of real bronze at a 

 tenth of the cost. 



When metal moulds are used their first cost is very great, as they must bo made in 

 numerous separate pieces so as to liberate the castings. The joints and ornaments 

 have to be chased and accurately fitted at a great expense. Their use, however, re- 

 quires no skill in the workman, and the rapidity with which the zinc is cast, the mould 

 taken to pieces, and the casting removed, renders the operation a very rapid and 

 economical one. 



Such is a general view of the practice of founding. The details, however, which 

 are contained in the original article in the earlier editions of this Dictionary appear 

 so valuable that that article is retained in addition to the above. 



The essential parts of a well-mounted iron foundry, are, 



J. Magazines for pig irons of different qualities, which are to be mixed in certain 



