FREDERICK GUTHRIE ON THE THERMAL RESISTANCE OE LIQUIDS. 659 
§ 74. In order to calculate the number of heat-units arrested by a mass of liquid of 
given thickness and surface, we must proceed as follows. Take, for example, the depres- 
sion-difference for water, § 60, namely, 4T3 millims. This has, like all the other values 
of the resistances, been corrected for the calibre of the tube and for the variation in 
pressure. It is found from the Tables that 
or 
hence from 
we find 
4T3 millims. is equivalent to 0-02829 cub. centims., 
45 cub. centims. have become 45-02829 cub. centims. ; 
x°X 45x0-00366=0-02829 
#°=0T7177, 
that is, an amount of heat has been arrested which would heat 
45 cub. centims. of air through 0°T7177 C., 
or 
1 cub. centim. of air through 7 0, 72 9 6 5 C., 
or 
1 cub. centim. of water through 7"72965 X 0-237 X 0-001296, 
where 0-237 is the specific heat of air for constant pressure, and 0-001296 is the specific 
gravity of air (both referred to water). Consequently the heat arrested would heat 
1 cub. centim. of water through 0 o, 0023732 C. This number, therefore, expresses the 
number of heat-units arrested in 1 minute by a circular disk of water 53'34 millims. in 
diameter and 1 millim. in thickness. Hence the number of heat-units arrested in 1 
minute by a layer of water 1 millim. thick and 1 square decimetre of surface is 
0-0106. 
Calling U r the number of heat-units resisted, we thus find : — 
Number of heat-units arrested 
in 1 minute by 1 square decimetre, 
1 millim. in thickness when 
T=20°T7 C. and AT=10° C. 
U,. 
Water 0-0106 
Glycerine 0*0407 
Acetic acid 0-0888 
Acetone 0-0902 
Oxalate of ethyl 0-0938 
Sperm-oil 0-0938 
Alcohol 0-0963 
Acetate of ethyl 0-0963 
Nitrobenzol 0-1045 
Oxalate of amyl ...... 0-1060 
Butylic alcohol ...... 0-1060 
