29 
the same, or proportional advantages should not be obtained 
by a similar application of atmospheric air, when so circum- 
stanced as to prevent any further accession of vapour. 
For it is secondly, to the effect of heat on the rapidly pro- 
gressive accumulation of vapour in elevated temperatures, 
that we principally ascribe the deleterious effects of a sum- 
mer's air to the product of the blast furnace, and other pro- 
cesses of combustion. 
We have assumed the extreme points of temperature of 
summer and winter to be 13° and 80°, (though we have 
known the mercury several degrees both above and below 
those points,) and from the expansive power of vapour at 
those temperatures, taken its quantity in the air in summer to 
be 5.8 and 58 inches per cubic foot, and which at the 
specific gravity of .55, will give .001846, and .01846 oz. 
advoirdupoise, the weight of vapour in each cubic foot of air 
respectively. 
Supposing then 2000 such feet of air to be thrown into a 
furnace per minute, and some furnaces have much more, the 
respective quantities of vapour thrown in therewith, in winter 
and summer, will be 3.7 and 37 oz. weight per minute. Dr. 
Crawford by experiments purposely and carefully made, has 
stated that to decompose 1 oz. of water requires as much 
heat as would raise its temperature 9485° ; and Dr. Thomp- 
son states the specific caloric, or capacities of water and iron 
to be 1 and .1264, as 8 to 1 nearly, or the caloric requisite 
to raise the temperature of a given weight of water 1 degree, 
would raise the same weight of iron 8°, or 8 times the weight 
of iron to the same temperature. 
In our case it is not water but vapour that is thrown into 
the furnace; and vapour in its formation from water, per Mr. 
Watt's experiments, we must notice, has already taken up 
920° of caloric ; hence the decomposition of 1 oz. of vapour 
into its component gases of oxygen and hydrogen, will require 
a quantity of caloric sufiicient to raise 1 oz. of water 9485" — 
