1st. Proper workmanship and simple construction, using materials which
experience has shown to be the best, thus avoiding the necessity of
early repairs.

2nd. A mud drum to receive all impurities deposited from the water, and
so placed as to be removed from the action of the fire.

3rd. A steam and water capacity sufficient to prevent any fluctuation in
steam pressure or water level.

4th. A water surface for the disengagement of the steam from the water,
of sufficient extent to prevent foaming.

5th. A constant and thorough circulation of water throughout the boiler,
so as to maintain all parts at the same temperature.

6th. The water space divided into sections so arranged that, should any
section fail, no general explosion can occur and the destructive effects
will be confined to the escape of the contents. Large and free passages
between the different sections to equalize the water line and pressure
in all.

7th. A great excess of strength over any legitimate strain, the boiler
being so constructed as to be free from strains due to unequal
expansion, and, if possible, to avoid joints exposed to the direct
action of the fire.

8th. A combustion chamber so arranged that the combustion of the gases
started in the furnace may be completed before the gases escape to the
chimney.

9th. The heating surface as nearly as possible at right angles to the
currents of heated gases, so as to break up the currents and extract the
entire available heat from the gases.

10th. All parts readily accessible for cleaning and repairs. This is a
point of the greatest importance as regards safety and economy.

11th. Proportioned for the work to be done, and capable of working to
its full rated capacity with the highest economy.

12th. Equipped with the very best gauges, safety valves and other
fixtures.

The exhaustive study made of each one of these requirements is shown by
the following extract from a lecture delivered by Mr. Geo. H. Babcock at
Cornell University in 1890 upon the subject:

THE CIRCULATION OF WATER IN STEAM BOILERS

You have all noticed a kettle of water boiling over the fire, the fluid
rising somewhat tumultuously around the edges of the vessel, and
tumbling toward the center, where it descends. Similar currents are in
action while the water is simply being heated, but they are not
perceptible unless there are floating particles in the liquid. These
currents are caused by