32 
BRITISH ASSOCIATION.- 1835 . 
experiments; and as both air and gas are dry, and must have been, 
with at least a very high degree of probability, proportionally af¬ 
fected by variations of pressure, the precise influence of these, about 
which, indeed, philosophers are not agreed, do not require to be 
taken into consideration; nor is there anything further necessary 
for rendering the result thus obtained strictly comparable with 
those of other experimenters, than to reduce it, by the rule of three, 
to what it would be if the specific heat of air were *267, the num¬ 
ber by which it is usually represented in books at a mean altitude 
of the barometer. The following experiments on air and hydrogen, 
performed on the 4th of August, will illustrate the preceding de¬ 
scription. 
t t f d p 
Hydrogen. 68 48 20 30*114 
Air.. 68 43 25 30*114 
By applying to these results the equation a 
30 
p 
, we get 
Specific heat of air. =*2767 
Approximate specific heat of hydrogen . =*4092 
But the gas, upon analysis, was found to contain 5 per cent, of air. 
Hence the specific heat of the hydrogen supposed pure as deduced 
f d „ Q ) Yl 
from the equation x — ci -\—- — — becomes *5097. And *2767: 
^ (100— n) s 
•5097 :: *2670 : *4914 = the specific heat of hydrogen compared to 
that of air under a pressure of 30,—when water is represented by 
unity, or, what amounts to the same, when air is *267. 
The following table exhibits the results thus obtained ;—referred 
to air as the standard, the number for nitrogen being the mean of 
two; that for hydrogen of four ; that for carbonic oxide of three ; 
that for carbonic acid of three ; and that for nitrous oxide of two 
experiments. 
1 
Specific Heats of 
equal volumes. 
Specific Gravities. 
Specific Heats of 
equal weights. 
| Air. 
1*0000 
1*0000 
1*0000 
I Nitrogen. ... 
*9613 
*9722 
*9887 
1 Hydrogen. 
*1315 
*0694 
1*8948 
| Carbonic oxide. ... 
1*0508 
*9722 
1*0808 
| Carbonic acid. 
1*6677 
1*5277 
1*0916 
| Nitrous oxide. 
1*7802 
1*5277 
1*1652 
A bare inspection of this table would seem to justify the conclusion 
that, with a single exception, the different gases operated with have, 
under equal volumes, specific heats proportional to their specific gra¬ 
vities ; and of course that, under equal weights, they have the same 
specific heat. In the excepted case, that of hydrogen, the specific 
heat is nearly the double of that which would result from this law. 
