PROFESSOR H. B. DIXOX OX THE RATE OF EXPLOSION IN OASES. 157 
moving piston may fall below the true value, and the more rapid the explosion the 
greater this error may be. That the pressures registered, and, therefore, the specific 
heats deduced from them, vary with the instruments employed appears from a com¬ 
parison of the numbers obtained by M. Berthelot, and those of MM. Mallard and 
Le Chatelier in the explosion of cyanogen. According to Berthelot’s experiments, 
the specific heat of nitrogen and carbonic oxide is 6‘2 at 2500°; according to MM. 
Mallard and Le Chatelier, it is 7 ’2 at this temperature. Again the latter have 
determined the specific heat of the simple gases by adding measured volumes of 
hydrogen, oxygen, and nitrogen to electrolytic gas, and measuring the pressures 
produced on explosion. From the seven experiments''' made at temt)eratures near 
2000° (calculated), they obtain, as a mean, the number 5'6 for the specific heat of the 
elementary gases at this temperature ; in a former paper they gave the value 7'5 as 
the specific heat at this temperature. Neither of these values agrees with the 7'2 
deduced from their cyanogen experiment at 2500°. The great difficulties attending 
determinations of this nature, in spite of the skill and patience with which the 
French chemists have attacked the problem, still leave it an open question whether 
the specific heats of the simple gases increase with the temperature. 
§ 3. The observations 1 have made on the effect of changes of initial jiressure and 
temperature on the rate of explosion in gases are not such as might have been 
expected from the theory of ordinary sound-waves. There appears to be for each 
mixture a crucial 'pressure, above which variations of pressure do not afiect the rate 
of explosion. Below this point the rates fall with diminution of pressure. In the 
case of electrolytic gas an increase of pressure from one to two atmospheres increases 
the rate of explosion from 2821 to 2872 metres per second. When the electrolytic 
gas is largely diluted, an increase in pressure from one to two atmospheres has less 
effect. The following rates were found at one and two atmospheres for electrolytic 
gas diluted with oxygen, nitrogen, and hydrogen respectively ■ 
Table XLI. 
(1.) Mixture H., -f O^. 
Pressure. 
1 At. 
2 At. 
Rate of exjjlosioii . 
169G 
1718 
* ‘ Combustion des Melanp-es Gazeux,’ p 259. 
