.156 PEOFESSOR H, E. DIXON OX THE RATE OF EXPLOSION IN GASES. 
re-form a wave. If the jets were produced in sufficient number their average effect 
would be uniform. 
§ 2. The Specific Heat ofi Gases at High Temperatures. 
In calculating the theoretical velocity of the explosion-wave, I have assumed that 
the specific heats of the simple gases do not rise with increase of temperature. On 
the other hand, I have assumed that the specific heats of gases formed from their 
elements with a condensation of volume—such as steam, nitrous oxide, ethylene, etc. 
—are equal at a high temperature to the sum of the specific heats of their elements. 
Thus, I have taken the specific heat of steam at constant volume to be 7’2 instead of 
G'5, as given by determinations at low temperatures. In making these assumptions, 
I have followed the example of Berthelot in his investigations on the explosion- 
wave. But in his later work on the specific heat of the gaseous elements at very 
high temperatures, Berthelot comes to the conclusion that these specific heats rise 
so rapidly with an increase of temperature that they are doubled between 1600° and 
4400° C.* He arrives at this result b}^ exploding cyanogen to carbonic oxide in a 
bomb, and observing the pressures registered by a piston moving against a spring 
when the cyanogen is burnt by oxygen alone, and when nitrogen is added or oxides 
of nitrogen are used instead of oxygen. 
Table XL.— Berthelot’s Experiments on the Specific Heats of Simple Gases. 
Mixture. 
Pre.ssure 
developed. 
Temperature. 
, 
Specific Feat of 
No or CO. 1 
CoN.t + O 2 . . . . 
UL 
25*11 
C 
4394 
i 
1 
9-60 
C.No + Oo + UN. . 
20'67 
4024 
8-39 
CjN,. + 0. A 2N.. . 
15-26 
3191 
7-93 
CjNj + O 2 A • 
11-78 
2810 
6-67 j 
C.N. A 2X0 . . . 
23-34 
4309 
9-85 
C 2 N 2 A 2 N 2 O . . . 
26-02 
3993 
8-43 1 
These values of the specific heats depend upon the accuracy with which the 
maximum pressure developed in the explosion is registered by the moving piston. 
Now the more rapidly the combustion takes place, the more nearly does the pressure 
exerted resemble a blow. I have found that a short column of mercury in a pressure- 
gauge suffers a far greater movement under the influence of a slow explosion than it 
does under the influence of a rapid explosion, although the quantity of heat evolved 
and the specific heats of the products were nearly the same in the two cases. No 
doubt this gauge was less sensitive to sudden pressures than the instrument used by 
M. Berthelot ; but the experiment warns us that the pressures registered by a 
* ‘Alin. Cliiin. ct Plijs.’ (VJ.), \ ol. 4, p. 06. lytsti. 
