FREDERICK GUTHRIE ON THE THERMAL RESISTANCE OF LIQUIDS. 
653 
It appears from the above Table that warm water conducts more heat than cooler in 
the same time for the same temperature-difference. The temperature-difference being 
constant (5°55 C.) the corresponding expansions are in one minute 
from T =13-06 fromT 1 =18 , 61 fromT 2 =24T6 fromT 3 =29-71 fromT 4 =35-26 
to T 1= =18-61 to T 2 =24T6 to T 3 =29-71 to T 4 =35-26 to T 5 =40-81 
Expansion =10. Expansion =10. Expansion =11 ’4. Expansion = 15. Expansion =19. 
We also conclude from the above deduced values, not only that the resistance dimi- 
nishes with the temperature, but also that the diminution of resistance is greater for 
equal increments of temperature at higher than at lower temperatures. 
§ 53. The first of these results, namely, that resistance diminishes with increase of 
temperature, agrees fully with the result given in §§ 43, 46, that the rate of penetration 
t is less for less temperature-differences than for greater ones. The cause of the more 
speedy penetration of great heats is in fact due to the less resistance offered to the pas- 
sage of the heat by those portions of the liquid which have already been heated. 
VII. Influence of Constitution of the Liquid on the quantity of the Heat which passes. 
§ 54. In experimenting in the manner described in §§ 15, 16, M. Despretz con- 
cluded that the conductivities of fresh and salt water were virtually the same. The im- 
portant cosmical bearing of this question induced me to examine it by means of the dia- 
thermometer, and at the same time to examine the relative conducting-powers or resist- 
ances of some other aqueous solutions. Preliminary experiments having shown that the 
resistances of such solutions were very nearly the same as that of water, I have preferred 
for the present the examination of saturated, or nearly saturated solutions to those which 
contain either equal or equivalent amounts of solid salt. The solutions of the pure 
salts were saturated at the atmospheric temperature, and a single drop of water was 
added to each to prevent crystallization during the experiment, which would of course 
vitiate the result. The results are given, as before, in corrected millimetres of depres- 
sion; the numbers are in the proportion of the numbers of heat-units arrested (comp. § 50). 
T=l°9*72 
AT =20 
d=2 millims. 
£j=l min. 
milRms. 
millims. 
millims. 
Mean resistance, 
millims. 
Distilled water 
99-64 
101-77 
100-71 
100-70 
Chloride of sodium (nearly sat.) 
101-11 
101-72 
101-47 
101-43 
Chloride of calcium ( „ „ ) 
105-68 
104-43 
104-96 
105-02 
Carbonate of potassium („ „ ) 
109-20 
107T3 
111-47 
109-26 
The two latter of these substances were chosen on account of their great solubility. 
4 s 
MDCCCLXIX. 
