405 
Chemistry. — “J/nvestigations on the Vemperature-coefficients of 
the Free Molecular Surface Energy of Liquids between —80° 
and 1650° C.”: XVII. The relations between the Molecular 
Cohesion of Liquids at their Melting- and Boilingpoints, and 
their absolute Melting- and Boiling-temperatures respectively”. 
By Prof. Dr. F. M. JArGer. 
(Communicated in the meeting of June 24, 1916.) 
§ 1. Some eight years ago already P. Watprn’) drew attention in 
a number of interesting papers to the remarkable empirical relations, 
which seem to be present between the capillary constants of non- 
associated liquids at their boiling- and meltingpoint, and these tem- 
peratures themselves, if expressed in terms of the absolute scale. 
Starting from the empirically stated rule, according to which the 
quotient of the heat of evaporisation and of the specific cohesion 
at the boilingpoint : = oscillates closely about a mean value of 
ah 
17,9, if the liquids are not appreciably associated, — he found by 
combination of this rule with the so-called “rule of Trovuton’’, 
according to which in the case of normal liquids the quotient of 
the molecular heat of evaporisation and of the absolute boiling- 
Q 
temperature : nn should be a constant ( 20,7), — the relation: 
b 
Ma’), (156 
KE 
By analogous reasoning WArLDEN found also for substances at their 
meltingpoint a similar relation; the mean value, round which the 
said quotient oscillates, should in the case of non-associated liquids, 
be: 3,65. For associated liquids, however, both mean values should 
be appreciably smaller. Both, of course only approximative empirical 
rules, may be formulated as follows: 
At the melting- and boilingpoint of the substances the quotients of 
the molecular cohesion and the absolute melting-, respectively boiling- 
temperatures themselves, are almost constant for non-associated liquids. 
WarpeN checked these conclusions by means of a number of 
cases, collected from literature; and he found them really confirmed, 
at least within certain limits. However, in the case of the inorganic 
salts no such mean value could be derived from the older data in 
literature. 
§ 2. It seemed interesting to test these relations once more by 
IP. WALDEN, Zeits. f. phys. Chemie 65, 257 (1909); Zeits. f. Elektrochem. 14 
713, (1908. 
