ON THE HEAT OF COMBINATION. 65 
tube will fail to render different parts of the scale accurately comparable with 
one another to a five-hundredth part. The general method pursued in the 
determination of the following specific heats was the same which I described 
some years ago*; but to avoid the uncertainties just referred to, alternate 
experiments were made with pure water and with the solution, under condi- 
tions as nearly as possible identical, and these were repeated till accurate 
means were obtained. By this mode of operating, a very great degree of 
precision may be given to experiments of this kind. 
The only salts whose solutions have yet been examined are the nitrate of 
potash, the nitrate of soda and the chloride of sodium. They were all chemi- 
cally pure. The density of each solution compared with water at the same 
temperature was also determined. 
The first solution of nitrate of potash contained for every 100 parts of 
water 25°29 parts of the salt. The thermal values of the thermometer with 
large reservoir described in the paper already referred to, in terms of this 
solution and of water, were found in alternate experiments to be— 
Solution I. Water. 
5044 ¢ 4095 
504:7 4107 
5050 4116 
Mean.... 5047 4106 
The temperature of the air during these experiments varied only from 
18° C. to 18°5 C. 
The second and third solutions contained respectively 12°645 and 6:322 
parts of nitrate of potash for 100 parts water. Air from 185 to 189. 
Solution II. Solution III. Water. 
4600 4393 4118 
4620 4387 4105 
4605 4385 4108 
4610 aati 
Mean.... 4610 4387 4110 
From these data the specific heats of these solutions at the temperatures at 
which the experiments were performed, as compared with water at the same 
temperatures, may be easily computed. I have given them in the following 
table, as also the specific gravities of the liquids. 
5 Il. Iii. 
Specific heat .......... 0°8135 08915 = -_- 09369 
Specific gravity........ 11368 1-0728 1:0382 
The solutions of nitrate of soda contained 42°49, 21:245 and 10°622 parts 
respectively of nitrate of soda for 100 parts of water. The temperature of 
_ the air ranged from 17%5 to 188 during these experiments. 
Solution I. Water. Solution II. Water. Solution III. Water. 
Le 
5261 4107 4775 4116 4499 4116 
5234 5117 4782 4098 4498 4098 
Ny 5247 4119 4787 4100 4488 4100 
_ Mean....5247 4114 4781 4105 4495 4105 
| ia Il. Ill. 
ig Specific heat .......... 0°7838 0°8585 09131 
yr, Specific gravity ........ 1:2272 ~ 11256 1:0652 
es amounts only to a few degrees ; and even in a close apartment the increased agitation of the 
_ air on a windy day sensibly increases the rate of cooling. 
* * Philosophical Transactions for 1844, p. 34. 
1849, F 

