ons of operation, as follows:

Class A. For stoker-fired furnaces where high overloads are to be
expected or where other extreme conditions of service are apt to occur.

Class B. For ordinary stoker settings where there will be no excessive
overloads required from the boiler or any hand-fired furnaces where the
rates of driving will be high for such practice.

Class C. For ordinary hand-fired settings where the presumption is that
the boilers will not be overloaded except at rare intervals and for
short periods only.

Table 61 gives the characteristics of these three classes according to
the features determining the quality. This table indicates that the
hardness of the brick in general increases with the poorer qualities.
Provided the hardness is sufficient to enable the brick to withstand its
load, additional hardness is a detriment rather than an advantage.

TABLE 61

APPROXIMATE CLASSIFICATION OF FIRE BRICK

________________________________________________________________________
| | | | |
| Characteristics | Class A | Class B | Class C |
|_____________________|________________|________________|________________|
| | | | |
| Fuse Point, Degrees | Safe at Degrees| Safe at Degrees| Safe at Degrees|
| Fahrenheit | 3200-3300 | 2900-3200 | 2900-3000 |
| | | | |
| Compression Pounds | 6500-7500 | 7500-11,000 | 8500-15,000 |
| | | | |
| Hardness Relative | 1-2 | 2-4 | 4-6 |
| | | | |
| Size of Nodules | Medium | Medium to |Medium to Large |
| | | Medium Large | |
| | | | |
| Ratio of Nodules | High | Medium to High | Medium Low |
| | | | to Medium |
|_____________________|________________|________________|________________|

An approximate determination of the quality of a fire brick may be made
from the appearance of a fracture. Where such a fracture is