Chat. XXI. STEAM CONSIDERED AS A MOVING POWER.

1253

Fig-1970. RECTANGULAR STEAM BOILER.

supplies the water; the steam passes to the engine by thepipe S, and when not required goes off through the safety-valve V, and through the pipes T, W.

To find the dimensions of a boiler without an internal flue,we must divide the solid content of the water it contains bythe area of the bottom: we thus obtain the depth of water ;then multiply the bottom and side surface for fire andflue, and divide the product by twice the capacity forwater, less the area of the bottom surface, and the resultwill be one of the dimensions for the bottom ; then dividethe bottom surface by the dimensions found, which givesthe other dimension. Cylindrical boilers, which are usedfor the production of high-pressure steam, may have theirdiameter and length found by adding their capacity forwater and steam together, and also the quantity of surfacefor the action of the fire ; then divide twice the capacityby the quantity of fire-surface for the diameter: the capacitymultiplied by 1 -27, and divided by the square of thediameter, gives the length of the boiler.

The Materials of which Boilers are usually made are either

4 l 3

Fig. 1975. boiler. 1976.