OF COAL AND RATE OF EVAPORATION, 31 
with the radiating fire surface. I was induced to have 
the cylindrical boiler, described under the VIII. head, 
altered to the new shape which is seen in Fig. 18. 
Under the cylinder boiler of 5 feet 6 inches in diameter, 
three smal] cylinders, each of 1 foot 6 inches in dia- 
meter, extending the length of the main boiler, were 
placed, and filled with water from the upper boiler. A 
line carried across the fire-place measured 4 feet 8 inches, 
while a line carried in the same direction, but over the 
surface of the boiler bottom and its appendages, measured 
17 feet 7 inches. When again used, the altered boiler 
proved unequal to the work of the original plain cylinder. 
It was found, indeed, when properly tested, to possess a 
_ remarkably low evaporating power, namely, from 5.5 to 
5.8 lbs. of water at 212° per pound of coal. 
The setting of the same boiler was then altered as seen 
in Fig. 19. 
Fig. 19. 
The lineal measurement of the absorbing surface was 
thus reduced to 10 feet 6 inches, while the line across 
the fire was the same as before. The new evaporating 
