﻿and Expansions of some Liquids. 1 45 



completely the carious fact established by M. Pfaundler, that 

 the first equivalent of water added to monohydrated sulphuric 

 acid increases the specific heat by a quantity precisely equal to 

 that of the water added, while for every further dilution there is 

 a very considerable loss of specific heat. This is probably con- 

 nected with the existence of the bihydrate as a perfectly definite 

 compound. 



Sulphate of Soda, Na 2 0, SO 3 + n Aq . 









( 



C 



-A. ^ 





n. 



c. 



P- 



Observed. 



Calculated. 



C-18w. 



50 



0-8890 



1042 



926-3 



926-3 



+ 26-3 



100 



0-9345 



1942 



1815 



1815 



+ 15 



200 



0-9625 



3742 



3602 



3602 



+ 2 



400 



0-9805 



7342 



7199 



7193 



- 7 



A solution with 40 equivalents of water crystallizing at the 

 ordinary temperature. I have not been able to operate on solu- 

 tions more concentrated than that containing 50 equivalents. 



The first three determinations lead to the formula 



n in t*oa 4094 98000 



C = lSn— 16-34 H -*— • 



n n l 



We see that for solutions containing more than 200 molecules 

 of water the specific heat is less than that of water alone, and 

 that the specific heat is always diminished by the addition of 

 water to a solution of sulphate of soda. 



Observations on the specific heats of these solutions have 

 already been published by M. Schuller*. His experiments were 

 not made on solutions of the same standard as those which I 

 examined ; but he has deduced from his results an empiric for- 

 mula by which the specific heat may be calculated for all propor- 

 tions of salt dissolved. This calculation, applied to the solutions 

 which I have studied, would give the following results, which I 

 have placed opposite to those obtained by me : — 





Observed. 



By 



Schuller's formula. 



0, S0 3 + 50 Aq 



0-8890 





0-8916 



+ 100 „ 



09345 





0-9392 



+ 200 „ 



0-9625 





0-9678 



+ 400 „ 



0-9805 





0-9835 



The differences, especially for the solutions with 100 and 200 

 equivalents of water, appear to me to exceed the errors possible 

 in my experiments. 



* Pogg. Ann. vol. cxxxvi. p. 70. 

 Phil Mag. S. 4. Vol. 41. No. 271. Feb. 1871. L 



