232 Dr. J. Monckman. Occluded Gases and [May 31, 



that the whole rod should be exposed to the same temperature. If 

 the rods are thick the changes in the contacts, even at ordinary tem- 

 peratures, become great in proportion to the resistance of the rods ; 

 and if thin there is great danger of them being changed by the heat. 



We found the method of electroplating with copper very good up 

 to 500° or 600°, after which it completely broke down, and we were 

 not able to get any other method to stand. Thus the experiments 

 were stopped there, although we expected other changes at 800° to 

 1000°, from the numbers obtained for the specific heat by Weber. 



The first method tried was that used by H. Muraska (' Annalen 

 der Physik und Chemie,' vol. 13, 1881, p. 310), in which a hole is 

 drilled in each end of the carbon rod, and after electroplating with 

 copper, a copper rod is pushed in tight and brazed in. The ob- 

 jections to this method were : 1st, requires a thick rod ; 2nd, better 

 contact formed as the temperature rises, tending to produce error in 

 the same direction as the results of the experiments. 



Second. Forming a contact that would be liquid at all tempera- 

 tures above 100°. This was done by drilling vertical holes near the 

 ends of the rods, and filling them with fusible metal. Required thick 

 rods, gave way. 



Third. Used thin rods so that the change in contact resistance 

 might not bear so large a proportion to that of the rod itself. Glass 

 vessels shaped as in fig. 11 were prepared, and the rod packed at A 



Fig. 11. 



and B with asbestos. Fusible metal or solder was melted into the 

 glasses, and the rod protected by a glass tube B. 



Fourth. An attempt was made to form contacts by inserting the 

 thin rod into cavities drilled into thick rods of carbon, and joining 

 by Indian ink, sugar and graphite, &c. 



Lastly, the rod was incased in thin sheet asbestos, well coated with 

 wet clay between each layer. The ends were electroplated with 

 copper and tinned. They projected beyond the asbestos covering 



Fig. 12. 



