The manufacture of these wheels was commenced in 1847, and in 1850, 15 tons weight were cast per day. The foundry and works as now completed are calculated to turn out 40 tons per day.
In another establishment the wheels while hot are lifted from the mould, and the centre part is placed in a hole communicating by means of a flue with a high chimney, and the edge is packed round with sand. A draft is thus created which cools the mass of iron near the centre of the wheel, and in some measure prevents it from contracting unequally during the operation.
At a foundry in Worcester, Connecticut, the wheels when east were taken hot from the moulds, and immersed in a pit of white sand, where they are left to cool gradually.
In order to obtain the best chill, it is considered necessary to use cold blast iron made with charcoal.
10. Railroad Spikes.—There is a large demand for railroad spikes in the United States.
On nearly all the railroads the rails are laid on transverse wooden sleepers, and are simply fastened down by large iron spikes with projecting heads, except at the junction of two rails, where the ordinary chair is employed.
In a manufactory at Pittsburgh, a machine
