378 Dr. T. Carnelley on the 



deal at this subject, and have come to the following conclu- 

 sions : — 



(1) The melting-points of those . compounds the atoms of 

 which are symmetrically arranged, are higher than in the case 

 of compounds in which the atomic arrangement is asymme- 

 trical. (2) The stability (and therefore the heat of formation) 

 of symmetrical compounds is greater than that of asymme- 

 trical compounds isomeric with them. If this be true, then 

 it would follow that the heats of combustion of the former 

 compounds are less than those of the latter. 



The application of the first of these conclusions may be 

 made, first, to isomeric compounds, and, secondly, to com- 

 pounds belonging to the same homologous series ; whilst the 

 second refers of course only to isomeric compounds. I re- 

 serve, however, the details of this investigation for a future 

 communication. Since working this subject out at some 

 length, I have noticed that Mr. Henry Watts, F.R.S., in the 

 last Supplement (vol. viii. p. 221) of his ' Dictionary of Che- 

 mistry ' has shown in a very clear and decisive manner that 

 " The more symmetrical the constitution of a benzene deriva- 

 tive, the greater is the resistance which it offers to the passage 

 from the solid to the liquid state," or, in other words, the 

 higher the melting-point. 



Freezing-points of Saline Solutions. — De Coppet (Ann. 

 Chim. Phys. [4] xxiii. p. 366, xxv. p. 502, xxvi. p. 98) has 

 shown, as the result of a long series of experiments, that for 

 bodies belonging to the same molecular group the coefficient of 

 depression of the freezing-point is inversely as the molecular 

 weight ; i. e. the molecular depressions of the freezing-point are 

 equal. A similar relation also exists between the molecular weights 

 of salts and the lowering of their temperatures of maximum den- 

 sity, and affords for the solutions of a large number of salts 

 the means of calculating the temperature at which they freeze, 

 and also that at which they possess a maximum density. For 

 a large number of bodies also the molecular depression of the 

 temperature of maximum density is nearly four times as great 

 as the molecular depression of the freezing-point. The first 

 of these statements is illustrated as follows : — 



Molecular Coefficient of Molecular 



weight. depression of depression, 



A. freezing-point, h. Axh. 



KC1 74-6 '451 33-61 



KBr 119-1 -292 34-8 l r 



KI 166-0 -212 35-2J 



KN0 3 ... 101-0 -267 27-0 



NaN0 3 ... 85-0 -310 26 



°4 



