38 METALLURGY OF CAST IRON.
pressed or knocked inward against the pressure of the stock in the furnace until it is in its right place. After this is done, any clay that might block up the hole in the tuyere to prevent blast to the furnace is broken away by means of a bar, and after the water pipes are attached, the blast is again put on. The removal or insertion of furnace tuyeres is an operation very readily performed, owing to the taper seen in the stationary sleeve at T, Fig. 6. This stationary tuyere support is cast hollow, of the same metal as the tuyere proper, and is kept cool by a flow of water going in at W and coming out at F. It is very rare that one of these sleeves has to be removed, as they do not project into the furnace, as is the case with the tuyere proper.
Coolers are very important in furnace construction to provide means to assist in lengthening the life of a lining. Some furnaces are better provided with cooling appliances than others. In the furnace shown, water is admitted to a suspended cast-iron receiver (as seen at X), which encircles the furnace, excepting an opening of about two feet at the front or breast side of the furnace. The cold water is admitted to this receiver in its lower division at M, and after having done its work it flows into the upper division and is carried off through the waste pipe N. The pipes Y are those which admit the cold water to the coolers, and P those returning the heated water to the waste receiver. At V V V are seen some of the many coolers which are built in the furnace lining to preserve its life. In the furnace shown these are placed in layers about thirty inches apart in height, and has about two feet of space between them. vSome furnaces have them built much closer than this, both in heighte metals are jf|V