The capacities of injectors are denoted by the diameters of their throats in millimetres; thus No. 4 has a diameter of 4 millimetres = 4 X .0394 = .1576 inches.

The expenditure of steam increases with the proportionate pressure in the boiler.

Raising the Safety-Valve of a Boiler will lessen the pressure by allowing the steam to escape from the boiler, thus permitting the water to rise up and come in contact with the over-heated iron, and probably cause an explosion.

The Door and Damper should never be open at the same time, unless it is absolutely necessary, as the cold air, that would otherwise have to pass through the fire and become rarified, rashes through the open door above the fire, and impinges on the tube and crown-sheets, and has a tendency to contract the seams and cause them to leak.

Blowing out the Boiler under a high steam pressure, the change is so sudden that it has a tendency to contract the iron, and cause the boiler to leak.

To heat Rooms, 1 square foot of steam-pipe surface is required for 80 cubic feet of space; 1 cubic foot of boiler is required for 1500 cubic feet of space. One horse-power boiler is sufficient for 40,000 cubic feet of space.