OF COAL AND RATE OF EVAPORATION. 29 
Fire-place 4 feet 3 inches by 6 feet, equal to 25.4 square 
feet of fire surface. 
Fire-bars 21 inches below the crown or arch forming 
the bottom of the boiler. 
Bars half inch thick with half inch spaces. 
Internal flue 29 inches in diameter. 
Boiler plates 5;*8s of an inch thick. 
Flues were carried round the boiler. 
When this boiler was worked at its usual speed and in 
ordinary circumstances the evaporating power was 8.33 lbs. 
of water evaporated from a temperature of 60°. 
At its ordinary speed it evaporated 26,440 lbs. of water 
from the temperature of 60° in 12 successive working 
hours. 
By adding to the above result one-sixth for the heating 
of the feed water from 60° to 212°, the evaporating power 
of the boiler will be 9.72 lbs. of water evaporated by one 
pound of coal. 
This boiler became a general favourite, and was used 
with the smallest of the cylindrical boilers (fig. 10) in 
most of my subsequent experiments. 
In making these experiments I found it the more neces- 
sary as I proceeded to guard myself against all bias from 
reasoning of a purely speculative character, and to avoid 
the smallest approach to anticipating results. The theo- 
retical part of the inquiry will be best treated separately, 
and I hope to take it up on some future occasion and to 
have the pleasure of laying the results before the Society. 
The simple object I have hitherto had in view was to 
learn how to consume as little coal and evaporate as much 
water as possible, and to acquire that knowledge by ex- 
periment alone. My method was to alter the flues, damp- 
ers, draughts, bridges, fire-bars, fires, coals, and stokers, and 
everything else connected with a particular boiler outside 
and inside, and then, if necessary, to alter back again, 
