TIII.KMAL PROPERTIES OF CARBONIC ACID AT LOW TEMPERATURES. 97 



difli'ivnces between the total heats at O 8 C. and at a few other temperatures. These 

 quantities refer to heating along the limit curve and not to heating at constant 

 pressure. 



Specific Heat of the Gas. (Fig. 6.) 



No experimental determinations of this quantity appear to have been made at 

 temperatures below C., though much work has been done at high temperatures. 



The specific heat is believed to vary considerably near the limit curve. Our 

 measurements give a mean value for a moderate range of temperature, starting in 

 each case a few degrees above the limit curve ; they are probably not correct for 

 higher temperatures than those at which they were measured. They are only used 

 for the small correction given in column y, Table VI., and for plotting the pressure 

 lines in the superheated area. 



Latent Heat of Liquid CO.,. 



Our ol>servations were plotted and values read off the smooth curve are given in 

 Table VI. The figures are probably correct to about per cent, from +20 C. to 

 30 C. and to 1 per cent, at 50 C. One point, at 8 '6 C. lies 1 per cent, off 

 the curve. This was the result of the first experiment made, when the spring 

 I >a lances were still used for weighing the CO.). The trace of air present only 

 produces a proportionate error in the value of L, i.e., '073 per cent., which is 

 negligible. 



No experimental determinations of L below zero have been published. REGNAULT* 

 made a single determination at +17 C. ; CHAPPUIS (13) a single determination at 

 C. and MATHlAs(l2) made a series of measurements between +6 C. and +31 C. 

 CAILLETET and MATHIAS (ll) calculated L from their own determination of the 

 liquid and vapour densities and REGNAULT'S pressure-temperature curve. KUENEN 

 and ROUSON (9) calculated L from AMAGAT'S (5) vapour density (extrapolated) and 

 BERN'S (o) liquid densities and their own pressure-temperature curve. MOLLJER(I) 

 calculated L from AMAGAT'S (5) vapour and liquid densities (extrapolated) and the 

 compound pressure-temperature curve mentioned above, based on AMAGAT and 

 REGNAULT'S results. 



All these results are plotted in fig. 18 beside our curve. If the drawing is examined 

 it will be seen that the mean of all the previous determinations lies above our curve. 

 We have investigated the causes of this divergence in detail as it appeared to cast 

 some doubt on the accuracy of our results. The investigation has shown, first why 

 the previous results tend to agree amongst themselves, secondly why they differ from 

 ours, and, finally, has resulted in an indirect confirmation of our results. 



* Recalculated by MATHIAS (12). 

 VOL. CCXIII. A. O 



