Actual work done: 
Units.
1,620 lb. of water raised from 60 deg. and turned
into steam at 53 lb..... ...................... = 1,855,900
Loss by radiation and convection................. 70,430
10-1/2 lb. ashes left, say at 500 deg................ 1,129
---------
Total work actually done.............. 1,927,459
Unaccounted for.................................. 26,521
---------
Calculated available work........................ 1,953,980

The unaccounted-for work, therefore, amounts to only 11/2 per cent.
of the calculated available work.

Sir Frederick Bramwell ingeniously arranged his data in the form of a balance sheet, and showed 253,979 units unaccounted for; but if from this we deduct the work lost in displacing the air, the unaccounted-for heat falls to less than 4 per cent. of the total heat of combustion.  These results show how extremely accurate the observations must have been, and that the loss mainly arises from convection and radiation from the boiler.]

The data necessary for our purpose are: 

Steam pressure 80 lb. temperature 324 deg. = 784 deg. absolute. 
Mean temperature of smoke 389 deg. = 849 deg. "
Water evaporated per 1 lb of coal, from and at 212 deg. 11.83 lb. 
Temperature of the air 60 deg. = 520 deg. absolute.
     " of feed water 209 deg. = 669 deg. "
Heating surface 220 square feet. 
Grate surface 3.29 feet. 
Coal burnt per hour 41 lb.

The fuel used was a smokeless Welsh coal, from the Llangennech colleries.  It was analyzed by Mr. Snelus, of the Dowlais Ironworks, and in Table II. are exhibited the details of its composition, and the weight and volume of air required for its combustion.  The total heat of combustion in 1 lb of water evaporated: 

= 15.06 x (0.8497 + 4.265 x (0.426 — 0.035/8))
= 15.24 lb. of water from and at 212 deg.
= 14,727 units of heat.

TABLE II.—­PROPERTIES OF LLANGENNECH COAL.

---------------------+----------+------------+---------

------------+
|          |            |                     |
|          |            |    Products of      |
|          |  Oxygen    | Combustion at 32 deg.  F.|
| Analyses | required   +--------+------------+
| of 1 lb. |    for     |        |            |
| of Coal. | Combustion.| Cubic  |  Volume    |
|          | Pounds.    | feet.  | per cent.  |
---------------------+----------+------------+--------+-----

-------+
Carbon...........   |  0.8497  |  2.266     |  25.3  |     11.1   |
Hydrogen.........   |  0.0426  |  0.309     |   7.6  |      3.4   |
Oxygen...........   |  0.0350  |    ---     |   ---  |      ---   |
Sulphur..........   |  0.0042  |    ---     |   ---  | _    ---   |