66 



Emission and Transmission of Heat 



from the perimeter of the opening, so as to avoid heating the wa- 

 ter in the tank, it is held in place by small wooden wedges. 



M 



Fig. 179 



Fig. 180 



855. In the other opening are placed the plates of which the 

 the conductivity is to be measured ; these rest against the stops R 

 R R R and their outer surface is heated by steam. Their con- 

 struction is suitably varied for solid or powdered material. In 

 figure 178 we have assumed the material under test to be solid; 

 figure 1 80 shows the construction on a larger scale; a b cd\s a rec- 

 tangular box of copper having one face provided with a large 

 opening shown in figure 181 and 182, the first of which is an eleva- 



Fig. 181 



Fig. 183 



tion of the face a b and the second a section perpendicular to this 

 face. Steam is admitted by the tube e f, and the water of con- 

 densation and along with it any excess steam escapes by the tube 

 g h\ a thin narrow rubber gasket is laid around the opening in the 

 face a b, and against this the plate is held by copper rods, hooked 

 at one end and provided with thumb screws at the other. The 

 vessel is fitted with a thermometer for ascertaining the tempera- 

 ture of the steam, and is surrounded by a wooden frame like that 



