portionate loss from that cause.

It therefore follows that we should burn our coal rapidly and at a high
temperature to secure the best available economy.

[Illustration: Portion of 9880 Horse-power Installation of Babcock &
Wilcox Boilers and Superheaters, Equipped with Babcock & Wilcox Chain
Grate Stokers at the South Side Elevated Ry. Co., Chicago, Ill.]

PROPERTIES OF WATER

Pure water is a chemical compound of one volume of oxygen and two
volumes of hydrogen, its chemical symbol being H_{2}O.

The weight of water depends upon its temperature. Its weight at four
temperatures, much used in physical calculations, is given in Table 10.

TABLE 10

WEIGHT OF WATER AT TEMPERATURES
USED IN PHYSICAL CALCULATIONS

+---------------------------+----------+----------+
| Temperature Degrees |Weight per|Weight per|
| Fahrenheit |Cubic Foot|Cubic Inch|
| | Pounds | Pounds |
+---------------------------+----------+----------+
|At 32 degrees or freezing | | |
| point at sea level | 62.418 | 0.03612 |
|At 39.2 degrees or point of| | |
| maximum density | 62.427 | 0.03613 |
|At 62 degrees or standard | | |
| temperature | 62.355 | 0.03608 |
|At 212 degrees or boiling | | |
| point at sea level | 59.846 | 0.03469 |
+---------------------------+----------+----------+

While authorities differ as to the weight of water, the range of values
given for 62 degrees Fahrenheit (the standard temperature ordinarily
taken) being from 62.291 pounds to 62.360 pounds per cubic foot, the
value 62.355 is generally accepted as the most accurate.

A United States standard gallon holds 231 cubic inches and weighs, at 62
degrees Fahrenheit, approximately 8-1/3 pounds.

A British Imperial gallon holds 277.42 cubic inches and weighs, at 62
degrees Fahrenheit, 10 pounds.

The above are the true weights corrected for the effect of the buoyancy
of the air, or the weight in vacuo. If water is weighed in air in the
ordinary way, there is a correction of about one-eighth of one per cent
which is usually negligible.

TABLE 11

VOLUME AND WEIGHT OF DISTILLED WATER AT
VARIOUS TEMPERATURES[12]

+-----------+---------------+----------+
|Temperature|Relative Volume|Weight per|
| Degrees | Water at 39.