SPECIFIC HEAT OF AMMONIA. 339 



The volume denoted by vn, is the specific vohime of the mixture of 

 Hquid and vapor, and is given by the relation 



^ = ^ (3) 



M 



where V = total inside volume of container, and M = total mass of 

 ammonia. Usually we shall write, simply, v with the subscripts 

 1 and 2 omitted but understood. However, whenever it is desired to 

 designate the particular specific volume at which these measurements 

 were made, we shall write ^2-6593, where 2.6593 is understood to be in 

 CCS. /gram. 



2. Laboratory Equation for Energy Input to Calorimeter. 



During the time that the heating current is on, alternate readings 

 are made of the voltage drop across the smaller coil of the volt box 

 and of the voltage drop across the standard 1 ohm resistance in 

 series with the heating coil. Between each pair of readings, the 

 e. m. f. of the potentiometer batteries was balanced against that of 

 the standard cell. 



For any one measurement, the current through the heating coil is 

 given by 



_ _ average voltage drop across standard ohm , . 



resistance of standard ohm at the observed temperature 



and the voltage drop across the heater, is given by, 



E — average voltage drop across smaller coil of volt box x ratio of 

 volt box coils (5) 



and the energy input to the calorimeter is given by 



8H = EI {h - k) (6) 



{h — ti) being the interval of time during which the heating current 

 is on. 



To distinguish between ammonia and calibration measurements, 

 the subscripts 1 and 2 are used, thus 5//i = the energy input for an 

 ammonia measurement, 8H2 = the energy input for a calibration 

 measurement. The temperature of the standard ohm was read at 

 the beginning and end of each measurement and the average of these 

 two readings used to compute the resistance required for Equation 4. 

 The temperature of the standard cell was also read at the beginning 

 and end of each measurement. 



