QUANTITY OF HEAT. SPECIFIC HEAT. 



71 



Corrections had to be made, however, for gain or loss of heat in 

 other ways during the experiment. On the one hand, the calorimeter 

 gains heat by conduction and radiation from the heating part of the 

 apparatus. This Regnault * assumed to be the same per minute through- 

 out the experiment. On the other hand, as the calorimeter rises in 

 temperature, it parts with heat by radiation and by conduction to the 

 surrounding air, the quantity lost being proportional to the excess of 

 its temperature. By observing the change of temperature for ten 

 minutes before the gas flows, and for ten minutes afterwards, the 

 quantity of heat conducted and radiated from the heating part of the 



Stirrer 



T Outflow 

 Stirrer 



FIG. 55. Regnault's Apparatus for the Determination of Specific Heat of 

 Gases at Constant Pressure. 



apparatus, and the quantity lost to the surroundings per 1" excess of 

 temperature, is calculated, and so the result is corrected. 



Neglecting corrections, if W = the weight of gas flowing, T = tempera- 

 ture of the oil-bath, t v t 2 = initial and final temperatures of calorimeter,^? = 

 water-equivalent of calorimeter and contents, s Specific Heat of the gas, 



Determination of the Specific Heat of a Liquid by Mixture 



with a known Solid. An obvious mode of determining the specific 

 heat of a liquid consists in heating a known weight of a solid of known 

 specific heat, and immersing it in the liquid contained in a calorimeter. 

 An equation like that of p. 66 (modified, of course, by the necessary 

 corrections) then serves to give us W, the water equivalent of the 

 liquid. Knowing its weight, we have at once its specific heat. 



Method of Cooling. In this method the liquid to be experimented 

 on is placed with a thermometer in a highly polished metal vessel, serving 

 as a calorimeter, and this is suspended by silk threads in a colder enclosure, 

 the walls of which are kept at some constant temperature. This may 



* Swann (Phil. Trans., A. 210, p. 231) has pointed out that Regnault's assumption 

 that the conduction from the heating apparatus to the calorimeter is the same during 

 the flow as before and after is an overestimate. The flow of hot gas through the 

 connecting tube will tend to raise the temperature of the part of the tube more 

 distant from the heater, and will so reduce the gradient and lessen the flow of heat. 

 Regnault therefore put down to conduction heat which was really carried by the 

 gas, and so he underestimated the specific heat (see below, p. 86). 



