én Combustion, and in the Condensation of Vapours. 303 
question, it would be indispensably necessary to know ac- 
curately the capacity of steam for heat, at different tem- 
peratures ; a thing unknown, and which is difficult to de- 
termine. 
Upon examining the subject attentively, we shall find, 
however, reasons for thinking that the capacity of steama 
for heat ought necessarily to be diminished with the ia- 
crease of its temperature. The following calculations may 
serve to elucidate this subject : 
In order to determine the highest degree of temperature 
which can exist in the midst of the greatest heat when pure 
hydrogen is the only combustible employed, and when the 
fire is fed by atmospheric air ; it is necessary to remark, that 
as oxygen and azote are intimately mixed in the atmo- 
sphere, the heat which results from the combustion of hy- 
drogen ought to be immediately divided between the vapour 
which results from the union of the hydrogen with the 
oxygen, and the azote which is found necessarily mixed 
with this vapour. 
In order to simplify our inquiry, we shall commence by 
supposing that all the oxygen which exists in the atmo- 
spheric air is employed. 
Th this case, as it requires 7°3333 pounds of oxygen to 
be united to one pound of hydrogen in order to compose 
8°3333 pounds of steam, and as the atmospheri€ air is com-= 
posed of 21 pounds of oxygen gas mixed with 79 pounds 
of azote; the 7°3333 pounds of oxygen which are united 
to one pound of hydrogen in order to form 8°3333 pounds 
of steam, ought to be found mixed with 27°587 pounds of 
azote: consequently the heat developed in the combustion 
of one pound of hydrogen ought to be also divided between 
8°3333 pounds of steam and 27°587 pounds of azote; and 
this partition ought to take place in the direct ratio of the 
weights of these two fluids, and of their capacity for heat. 
The capacity of the steam being to that of azote as 155 
to 0'7036 (according to Crawford), all the heat in question 
will be divided so as that the steam shall retain a part of it 
represented by the number 9°5832 ; (=8'3333 x 1°55) and 
the azote will receive the other part of it =1941 (being 
the product of 27°587 multiplied by 0°7036 ) 
Now as the two numbers 9°5832 and 19°41 are both in 
the proportion of 1 to 20254, it is evident that the tem- 
peaiurs will be the same which we should have if all the 
eat in question was equally divided between the steam 
which would result from the combustion of 3-0254 pounds 
of hydrogen, 7, e. between 25°2113 pounds of steam. 
And 
