﻿142 M. C. Marigaac on the Specific Heats ; Densities, 



to represent with fidelity the means of my experiments, I admit 

 that the fourth may very well be suppressed ; but I think that 

 the third should be, within one or two units, accurate. 



Sulphuric Acid. 



The acid used in my experiments had been purified by distil- 

 lation and brought exactly to the state of a monohydrate by 

 repeated congelation, until it no longer presented any sign of 

 melting at the temperature of 10°. 



For the monohydrated acid, and the mixtures of it with 5, 10, 

 15, and 25 equivalents of water, it was necessary to use a glass 

 vessel instead of the metallic one which served for the other ex- 

 periments. The results are comprised in the following Table : — 





c*. 



IPO, S 



3 + rcAq. 



C 





n. 



Observed. 



Calculated. 



C~18w. 







0-3315 



98 



32-5 







5 



0-5764 



188 



108-4 



108-4 



+ 18-4 



10 



0-7212 



278 



200-5 



200-5 



20-5 



15 



0-7919 



368 



291-4 



290-2 



20-2 



25 



08537 



548 



468 



468 



18 



50 



0-9155 



998 



914 



914 



14 



100 



0-9545 



1898 



1812 



1812 



12 



200 



0-9747 



3698 



3604 



3610 



10 



400 



0-9878 



7298 



7209 



7209 



9 



The empiric formula by means of which the above results were 

 obtained, and the specific heats of any other solution may be 

 calculated, is : — 



C = 18rc + 8-o8H 9 — H 5— 



n n z n* 



But it must be remarked that for solutions containing less 

 than five molecules of water it would give quite inaccurate results. 



Sulphuric acid is one of the bodies the specific heat of which 

 has been already made known by M. Thomsenf. His experi- 

 ments are not directly comparable with mine, because he refers 

 his solutions to anhydrous sulphuric acid, to which he supposes 

 added 5, 10, 20, &c. equivalents of water. But it is easy to 

 compare his results with those deduced from the preceding for- 

 mula for the molecular heats. We thus find, n having the same 

 signification as in the preceding Table : — 



* These values refer to a temperature of from 16° to 20°. 

 t Archives des Sciences Phys. et Nat. vol. xxxix. p. 153. 



