456 



REPORT — 1886. 



(Thomsen, i. 48.) 



The specific heat of substances in the liquid state is al-ways greater 

 than that of the same in the solid, but the diflPerence is in no case of 

 those recorded so great as the difference between -water and ice [except 

 ench things as chloral hydrate, in -which -water may be supposed to be 

 formed during fusion, and the solitary case of iodine, solid •05412 

 (Regnault) and liquid -10822 (Favre and Silbei-mann)]. The specific 

 heat of solid sodium nitrate is '278 (Regnault, ' Ann. Chim. Phys.' 1841, 

 i. ] 79), and in the liquid state it is -413 (Person, ' Ann. Chim. Phys.' 

 1847, xxi. 332). 



Hence the molecular heats are — 



Solid 23-63 

 Liquid 35-10 



If we assume the latter for the solution we have 



NaNOa 35-10 



25H2O 45000 



485-10 



The observed molecular heat of the solution NaN03 + 25H20 is 

 465-5 (Marignac), or 461 7 (Thomsen). Now suppose ^SHjO "more 

 water to be added, the molecular heat is not 465-5 +450=915^5, but 908 

 (Marignac), or 904 (Thomsen). And again Avhen 50 more molecules of 

 water are added the molecular heat is not 908 + 900=1808, but 1802-25 

 (Marignac), or 1791 (Thomsen), and so on. 



So that all the water added seems to be influenced, at least until a 

 very large quantity is present. In this case one molecule of sodium 

 nitrate can afi'ect the movements of 100 molecules of water, and prob- 

 ably more. 



This effect is doubtless connected with the changes of volume which 

 the solution undergoes on dilution. 



Marignac has given the results of the determination of the specific 

 heats of a number of salt solutions at different temperatures, but tlaough 

 it may be stated, as generally true, that the specific heat of a solution 

 increases with rise of temperature, the differences observed are too small 

 to afford much ground for speculation. They are generally much less 

 than the increase in the specific heat of water for the same range of 

 temperature, namely, from about 18° to 20° and from 20° to 50°, taking 

 even the lowest value which has been assigned by different authorities to 



