420 



DR. C. H. LEES ON THE THERMAL CONDUCTIVITIES OF SOLIDS 



With the apparatus in this form, determinations of the thermal conductivities 

 of water, ethyl alcohol, acetic acid, and glycerine were made. 



The values found in different experiments for the relative conductivities of water 

 and glycerine, and mixtures of them, were concordant, and are given in the following 

 table along with H. F. WEBER'S* values for water and glycerine between 9 and 15, 

 but experiments on ethyl alcohol and acetic acid showed discrepancies which were, 

 after some time, traced to the evaporation of the liquid at points not covered by the 

 middle disc. As most of the liquids to be tested were more volatile than water and 

 glycerine, it was decided to get rid of this evaporation by entirely enclosing the 

 liquid, and the apparatus used throughout the greater part of the investigation was 

 then constructed. 



Description of Apparatus. 



Between two nickel-plated copper discs, U and M , fig. 1 1 , p. 4 1 9, 4 centims. in diameter 

 and '3 centim. thick, a disc of glass, C, '28 centim. thick, was cemented by means of 

 thin layers of shellac. In order to prevent bubbles of air occurring in the layer of 

 shellac, the surfaces of the copper and glass discs to be cemented together were each 

 covered with a thin layer of shellac, which was allowed to dry. Both surfaces were 

 then smeared with glycerine, and slid carefully together, air being prevented from 

 getting between the surfaces by the presence of abundance of glycerine. Pressure 

 and heat were then applied, the pressure forcing out the glycerine and bringing the 

 layers of shellac into contact, and the heat joining them. Both contacts were made 

 in this way, and withstood a large amount of usage without coming apart. 



A flat spiral coil of platinoid wire, P, was placed on the top of the upper disc, U, 

 and was held down by a thin copper disc, C, MO centim. thick, screwed to the disc, U. 

 The coil was insulated from both discs by means of mica, and the surfaces of the 

 discs exposed to the air were varnished to give them the same emissivity. This 

 combination rested on the inner edge of a ring of ebonite, E, of 7 centims. external, 



* H. F. WEBEK, ' Berliner Ber.,' 1885, p. 809. 



t The upper numbers are percentages by weight ; the lower percentages by volume. 



t Taken from the table, p, 425. 



