402 BABCOCK. 



which have yet appeared are those of Osborne and Van Dusen.^^ 

 Using an aneroid calorimeter of special construction, the specific heat 

 both at constant volume and at constant pressure was determined 

 in the temperature region which is most useful in the refrigeration 

 industry,- 45° C. to + 45° C. 



Especial attention was paid to the elimination of heat transfer to 

 the surroundings. 



The final results of their measurements are expressed by the equa- 

 tion, 



cs, = 3 . 1365 - . 00057 6 + -^^r^ (38) 



(133 — 0) ^ 



where 6 is in degrees C, and the saturation specific heat of the liquid 

 is in Joules per gram degree C. 



These experimenters put the precision of their results at 1 part in 

 1000. 



The work of the present paper overlaps by about 15° the range of 

 Osborne and Van Dusen's measurements, and in this overlapping 

 region, differs from their results by about two and a cjuarter per cent. 

 The difference between the values of Vi, v-2, and L, used by Osborne 

 and ^^an Dusen, and the writer, is too slight to account for the differ- 

 ence in the saturation specific heats. 



In Table IV. are given the values of the saturation specific heat of 

 liquid ammonia, expressed in Joules per gram degree, for comparison. 

 Figure 10 shows graphically the various reported Aalues of the satu- 

 ration specific heat of the liquid. 



VIII. Critical Survey. 



The experimental method and apparatus described in this paper 

 were designed for the measurement of the specific heat of ammonia 

 as a function of temperature up to the critical point. From the 

 outset, the conditions met with at the higher temperatures determined 

 the design of the apparatus and placed a limit on the accuracy attain- 

 able. At the highest temperature reached, 125° C, the pressure in 

 the container was about 100 atmospheres, which necessitated a rather 

 massive container, which in turn gave rise to temperature lag difficul- 

 ties already discussed. Furthermore, to obtain measurements of the 

 specific heat in the region near the critical temperature, where it is 



25 Osborne & Van Dusen, Bull. Bur. of Standards, 14, p. 39r. 



