TIIHIiMAL I'ROl'KIJTIKs (i| CAIHIONIC ACID AT LOW TEMPERATURES. 91 



found possible to make observations at temperatures below 30 C., and even at this 

 temperature the results were open to criticism as being small differences between 

 large measurements, see Table V. (first part). 



To get reliable results it was therefore necessary to design a special apparatus, 

 combining two thenin ^junctions and a throttle, which should not allow of appreciable 

 radiation. Experience with the original apparatus showed that the throttle had to 

 be adjustable to enable the required pressure ranges to 1*3 obtained. After one or 

 two experiments the apparatus shown in fig. 16 was made and answered perfectly. 



H. Steel tube. 



K. Ebonite tube. 



L. 



M. Copper jauze plug. 



N. Inlet. 



Outlet. 



Iron yoke. 



Vulcanite block for 

 control exp c . s . 



Ebonite valve body. 



Packing. 



Brass gland. 



vaJve spindle. 

 " valve. 



Ebonite distance piece 

 Brass cap. 



Fig. 16. 



The body of the valve is vulcanite, the gland and screw are brass, but the screw is 

 insulated from the passage through the valve by an extension rod of vulcanite. A 

 minute brass valve is inserted under the extension rod, and is the only metal 

 encountered by the CO., in passing through the valve. The two thermo-junctions are 

 held in vulcanite plugs inserted in the steel tubes on either side of the valve. They 

 project inside the inner vulcanite tubes, shown in the figure. The outer space forms 

 a jacket of CO 3 at approximately the same temperature as the inner space which is 

 entirely protected by the vulcanite tubes from any external influence. Vulcanite is 

 one of the best thermal insulators the specific conductivity is given by KAYE and 

 LABY as '00042. The whole apparatus is held together by an iron yoke, and can be 

 taken to pieces in a moment by slackening one of the set screws at the end. The 



N 2 



