EXPERIMENTAL KNOWLEDGE OF THE PEOPERTIES OF MATTER. 489 



0° and 200° is greater than, but very little different from, that of the 

 same volume of air under the same conditions. 



And, for nitrogen, the heat-capacity between 0° and 200° is about the 

 same as that of the same volume of air or of oxygen, for atmospheric air 

 consists mainly of nitrogen and oxygen. 



For hydrogen between about 0° and 200° the specific heat -was found 

 in four experiments to be : — 



3il96 



3-40i2 



3-4108 



8-4014 



of -which the mean value is 3"4090 for specific heat of hydrogen under 

 the conditions of atmospheric pressure and any temperature between 0° 

 and 200°. For low temperatures, as between 10° and —30°, Regnanlt 

 got a mean value 33996, agreeing fairly with the value for higher tem- 

 peratures. As in the case of oxygen, so here, multiplying the four results 

 by 0-0692, the specific gravity of hydrogen (air = 1), the mean of the 

 results compared with 0-2375 is the heat-capacity of hydrogen gas 

 compared with that of an equal volume of air ; this is 0-2359 to 02375 ; 

 thus the heat-capacity of hydrogen is sensibly the same as that of an 

 equal volume of air, the experiments giving for hydrogen a very slightly 

 lower value. 



On the above results Eegnault remarks that air and gases, which at 

 ordinary temperatures obey Boyle's law, are equally expanded by equal 

 increments of temperature up to temperatures as high as and higher 

 than 300° ; and that, as shown above, the heat-capacity of air is the same 

 for equal temperature-intervals independently of the initial temperature 

 as measured by the dilatation of air (by an air- thermometer) ; and, as 

 the same constancy is observed in the case of other gases which obey 

 Boyle's law, shall we not, he asks, he led to admit that the air-thermometer 

 indicates temperatures in a manner proportionallij to the quantities of heat 

 which it receives.'' (p. 109.) 



In the case of the first seven of the above gases the specific heat 

 remained constant up to 200°, and these seven are gases -which very 

 approximately obey Boyle's law. It is to be remarked that in the case of 

 these the heat-capacities of equal volumes are very nearly equal at atmo- 

 spheric pressure. 



In the case of chlorine, and still more of carbon dioxides and nitrous 

 oxide, the heat- capacities of equal volumes vary -with the temperature, 

 the values for a given range of temperature being less the lower the 

 mean temperature of the range and increasing as this temperature rises 

 up to 170° in these experiments; the specific heats therefore increase 



