S2 
Steam Engine- 
form, all the caloric which raised the temperature of eight 
pounds of iron filings from 212^ to 300®. 
2. The quantity of caloric, which thus becomes latent 
during the formation of steam, may be approximated, by 
repeating the following experiment of Dr. Black : He 
placed two cylindrical flat bottomed vessels of tin, five 
inches in diameter, and containing a small quantity of 
water at 50®, on a red hot iron plate, of the kind used in 
kitchens. In four minutes the water began to boil, and 
in twenty minutes the whole was boiled away. In four 
minutes, therefore, the water received 162® of tempe- 
rature, or 40i® in each minute. If we suppose, therefore, 
that the heat continues to enter the water at the same rate, 
during the whole ebullition, we must conclude that 40a® 
X 20® =810 have entered the water, and are contained 
in the vapour. 
It has been found by experiment that 75 pounds of 
Newcastle coal, or 100 pounds of coal of medium quali- 
ty, applied in the best manner, are required for the vapo- 
rization of 12 cubic feet, or about 89| wine gallons of 
water. A pound of coal, on the average, may be consi- 
dered as equivalent to convert a gallon of water into va- 
pour.^ 
VII. Water, by conversion into steam, has its bulk pro- 
digiously enlarged; viz, according to Mr, WatVs experi- 
ments, about 1800 times, A cubic inch of water (or 252 
grains) occupies, therefore, when converted into steam, 
the space of rather more than a cubic foot. Hence its 
specific gravity, under the ordinary pressure of the air. 
is to that of common air, nearly as 450 to 1000, or 9 to 
20 . 
* The consumption of coal in Boulton and Watt’s steam en- 
gine's about 5 Jib. per hour for the power of one horse: that is a 
power equal to the raising SS^QOOlb, one- foot high in a minute. 
T. C 
