ON THE PHENOMENA AND THEORIES OF SOLUTION. 



4,31 



The contraction consequent on the first addition is greater than the 

 second, and for each succeeding molecule is a diminishing quantity, 

 becoming rather less than 1 after addition of 3H2O. 



A similar result ensues if we calculate the conti'action following upon 

 the dilution of liquid H2SO4 with successive quantities of water. 



Take now another case, that of common salt (see diagram 2). 



The heat of solution of NaCl in IOOH2O is — 1180, a negative quan- 

 tity. On adding more water to a solution of sodium chloride a further 

 absorption of heat is observed. Thomsen gives the following values : — 



(NaCllOHoO) + 40H2O=-528; 

 (NaClSOHjO) + 60H,O=-]27; 

 (NaCl IOOH26) + IOOH2O = - 50. 



So that heat of solution of NaCl in 



10H2O= - (1180-655)= - 525; 

 5OH2O = - (1180 - 127)= - 1 05.3 ; 

 2OOH2O = - (1180 + 50) = - 1230. 



Tracing now the changes of volume which attend the processes of 

 solution and dilution we get the following results : — 



Taking 2*15 as the density of the solid salt we have its molecular 

 volume = 27'1. Then the following are the molecular volumes of its 

 solutions : — 



nHjO 



11 = 10 

 n = 50 

 n = 100 



Another way of stating these results would be to set down the thermal 

 and volume changes resulting from the addition of successive molecular 

 proportions of salt to the same amount of water. 



From the foregoing results we find — 



NaCl + lOOHgO = - 1180 C. 



2NaCl + 100fl2O = - 2106 C. 



10NaCl + 100H,O = - 5250 C. 



Difterence 



per jMolecule 



926; 

 ••1^^=393. 



So that whilst the addition either of salt or of water to a solution of salt 

 occasions an absorption of heat, the solution of a molecule of solid sodium 

 chloride in a relatively large quantity of water is attended by the absorp- 



Nicol, Phil. Mag. June 1884. 



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