1502 
15.6° just as in the experiments 11—16 the heat would have been 
— 3.83 gramme calorie per gramme of ammonium chloride. 
The heat of transition per gramme of NH,Cl amounts therefore 
to 15.45 + 3.83 = 19.28 gramme calories or 1.08 kilogram calorie 
per gramme molecule. 
In table 5 the differences in the last column are partly to be 
attributed to the said difference in specific heat between water and 
solution. It ean be derived from the data of the literature that this 
difference for our solutions amounts to about 0.2 calorie per Gramme 
of NH,Cl. The values of the last column of table 5 are not directly 
comparable either on account of the difference in temperature of 
heating. Through the mode of calculation followed these corrections 
have been eliminated, as has been said. 
In table 7 the mean specific heats for the «- and p-modifications 
in the neighbourhood of the transition point have been recorded. 
PAB GE. is 
7 - - — —___- a _ — —— — 
ae Heat per Mean 
| Limits of the Temperat. | Heat : 
NP. temperature Hcl difference | difference | spechg 
4, 5, 6 16.15—158.6 —15.96 
20.45 9.60 0.469 
7, 8, 9, 10 16.0 —179.05 — 6.36 
vre el Es) 15.85—195.4 +19.17 
| 16.2 5:53 0.341 
14, 15, 16 | 16.2 —211.6 | —+24.70 
In these calculations the above correction for the difference in 
specitie heat between solution and water has been put zero; this 
will give rise to a small error here, because the difference in calori- 
meter temperature is only small in the experiments of table 7. This 
table yields the conclusion that in the neighbourhood of the transi- 
tion point the specific heat of the g-modification is smaller than that 
of the a-form. The difference of energy between the two modifica- 
tions, which amounts to 1,03 kilogram calories at the transition 
point, will therefore become smaller at higher temperature. 
11. The vapour tension of dry ammonium chloride. 
The determinations of the transition point ($$ 5 and 6) and of 
the heat of transformation ($ 10) in connection with Prof. Smrra’s 
recent researches on the vapour pressure line of ammonium chloride 
and on the degree of dissociation of the saturate vapour’) open a 
1) Smrrn. Journ. Amer. Chem, Soc. 86. 1363. (1914); 8%. 38 (1915). 
