654 FREDERICK GUTHRIE ON THE THERMAL RESISTANCE OE LIQUIDS. 
§ 55. Two aqueous solutions were now taken of salts whose metals in the elementary 
state have little resistance, namely, silver and copper. These were again compared with 
water. 
T=20-83 
AT=20 
(5=2 millims. 
1 min. 
Water. 
Nitrate of silver (nearly 
Sulphate of copper (nearly 
sat.). 
sat.). 
millims. 
millims. 
millims. 
Resistance 
(1) 
98-64 
106-64 
104-22 
(2) 
99-60 
104-23 
105-72 
Mean . 
99T2 
105-43 
104-97 
The difference between this value for water and the value given in § 54 may partly 
arise from the difference (0 O- 8) of T, but is more probably due to a minute error in e>, 
as the cones had been separated between these two experiments. It is also seen that 
there are in one or two cases greater differences between the determinations of the same 
substance than between those of different substances. In order to get results of suffi- 
cient accuracy for the establishment of the law of resistance under these circumstances, 
a very much greater number of experiments must be performed with an instrument of 
greater sensibility. I hope to be able to lay such results on a future occasion before the 
Society. 
§ 56. Meanwhile the following conclusions appear unavoidable, even from the above 
incomplete experiments. The solution of a metallic salt in water invariably increases 
the thermal resistance of the water. Those elements which dissolve in the water without 
increasing the bulk of the water, can only increase its thermal resistance by increasing 
its capacity for heat, which must in such cases be the sum of the capacities of the water 
and elements separately. The thermal resistance of a solid salt is greater than that of 
water, consequently when, as in the majority of instances, water is displaced by the salt, 
the increased resistance is due to the partial substitution of a body of greater resistance. 
This increase is partly counterbalanced by the inferior specific heat of the salt. The 
nature of the metallic base of the salt in regard to its thermal resistance in the free state 
has little influence upon the thermal resistance of the solution of the salt*. 
§ 57. The difference in thermal resistance between fresh and salt water must be of 
very considerable importance in thalattology, but the consideration of this would be 
beyond the scope of my present purpose. 
§ 58. A branch of the investigation of surpassing interest is the comparison of the 
resistances offered by liquids of entirely different chemical composition. In the experi- 
ments the results of which are given below, in order that the experiments might be 
as exact as possible, times were chosen at which the atmospheric temperature was the 
* I am inclined to think that it has none. Compare also § 70. 
