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 shape required, or the casting may be treated merely as the starting-point for a whole series of operations—forging, rolling, chipping, chasing, wire-drawing, and many more. Another property of the metals which must be noticed is, that not only can separate masses of metals be melted down and fused into one, but it is possible, under various conditions, of which the one invariably necessary is perfectly clean surfaces of contact, to unite separate portions of the same or different metals without fusion of the mass. For our present purpose the most important instance of this is the process of soldering, by which two surfaces are united by the application of sufficient heat to melt more fusible metal which is introduced between them, and which combines with both so as firmly to unite them on solidifying. Closely allied to this are the processes by which 70