14 
HEPORT— 1847 * 
evolved by the combioation of acid and water (when this heat ii not iu- 
creased by a new addition of water) are in the same proportion to each other 
as the numbers 10:6:4:3:2; or, with the exception of the first hydrate, 
which has the relative number 10 instead of 12, the heat produced isio 
inverse proportion to the number of atoms of water in the acid employed. 
But this is precisely the same rule which wc have discovered for the value of 
the maximum of contraction for the corresponding hydnitca. In order to 
make a comparison between the valtn* of the contraction and the quantity of 
heat observed by Hess, I have chosen that series of experiments which he 
himself seems to regard as the most complete uml moat accurate. The de¬ 
termination of the heat evolved teems yet to bo embarrassed with so great 
difficulties, that the several aeries of experiments, as well by one and the 
same as by different observers, at Irast as regards tire absolute quantity of 
heat, have given very ditferent results. 
Hess has thus found*, that when to an acid, of the composition stated 
below, an addition of water is given to that extent that the heat evolved is 
not further increased, then the heat produced by one atom of dry sulphuric 
acid is equal to the numbers in the 3rd column of the following table. 
Table VIII. 
No. 
Acid employed. 
Heat evolved. 
Number of 
proportion. 
1 
SO, + SHaO 
9.'>'2 ' 
1 
2 
ditto 
9S‘16 
\ 
2 or 4 
3 
SO, + 411,0 
76-971 
1 
4 
ditto 
77-5 J 
§ or 3 
5 
SO, + GHoO 
47*8 "1 
6 
ditto 
46-73 
1 or 2 
7 
ditto 
46-80 1 
8 
SO, + 2HoO 
134-2 
ditto 
134-2(1)11 
3 or 6 
Hess canine portirjhV,,-® calculated the most probable value of .hat 
with a„ eaSrrf a^d'foTnd^^^ 
46-402 + 0-262 = 46-402 (1 + o-Ol 1281 
from winch value we obtain ^ 1^8), 
SO, + 2HoO 
SO, + 8HaO 
SO, + 411,0 
SOs -h 6HoO 
Table IX. 
j|( p ^ _ ‘rO tO 
Quantity of heat. 
Difference. 
Observed. 
Calculated. 
134-20 
94-18 
77-23 
46-94 
189-21 
92-80 
69-60 
46-40 
— 3-01 
+ 1-38 
+ 7-63 
+ 0-54 
