AND LIQUIDS AND THEIR VARIATION WITH TEMPERATURE. 423 



The value of k a and h are known from the observations made in Part I. 



The value of A is determined most accurately, by carrying out an experiment with 

 air substituted for the liquid, so that the term involving k t on the left-hand side of 

 the equation has a known small value. From the observations of temperature the 

 value of the right-hand side of the equation is calculated, and hence the value of A. 



Constants of Apparatus. 



r = 2 centims., therefore irr* = 12 '5 sq. centims. 

 r t i'855 centims., therefore -nr\ = 10'8 sq. centims. 

 t t = -127 



t Q = -281 therefore -- = '070 centims. 



t u = '320 + '075 = '395 centims. 

 efore ZTrrh -|- = 



and 2-vrh t x = '00148 



h = '00030, therefore ZTrrh -- = '00026 



Sum = '00174 



Method of Experimenting with Ebonite Ring Apparatus. 



In carrying out a determination of the thermal conductivity of a liquid, the surfaces 

 of the discs with which the liquid was to come into contact were cleaned, and the 

 lower nickel-plated surface of the middle disc wet with the liquid. Liquid was then 

 poured into the space inside the ebonite ring, till the upper surface of the liquid 

 was higher than the upper surface of the ring. The middle disc was then placed on 

 the ebonite ring with one edge touching the liquid, which was drawn into the space 

 between disc and ring by capillarity. The disc was then slid slowly over the ring 

 till the liquid was entirely enclosed, and any excess which flowed over the ring was 

 removed by filter paper. 



To prevent the upper discs moving during an experiment, they were secured to the 

 lower, either by a silk thread passing from one side of the lower disc over the upper 

 discs to the other side of the lower disc, or by a wire frame which could be attached 

 to the lower disc, and was provided with a screw which pressed on a small disc of 

 cork on the copper disc covering the heating coil. 



The combination was then placed in the air bath and the process described (p. 413) 

 carried out till the steady temperature state was attained, when the observations of 

 power supplied, temperatures, and temperature differences were made. 



Experiments were made on four liquids, with the results given in the following 

 tables and curves. 



