ON THE THERMAL CONDUCTIVITY OF CAST IRON. 

 By E. H. Hall and C. H. Ayres. 



Presented October 12, 1898. Received December 6, 1898. 



Two or three years ago an article entitled " On the Thermal Conduc- 

 tivity of Mild Steel " was published by one of the authors * of the pres- 

 ent paper. The method described at length in that article made use of 

 a disk of soft steel, about 0.3 cm. thick and about 10 cm. in diameter, 

 coated on each face with an electrolytic deposit of copper about 0.05 cm. 

 thick. Thin copper wires attached electrolytically to these copper coat- 

 ings led to a sensitive galvanometer, the deflections of which depended 

 upon the thermo-electromotive force of the couple made by the steel of 

 the disk and the copper of its coverings, and indicated the difference of 

 temperature existing between the two faces of the steel itself. 



"Water of a known temperature was made to flow across one copper 

 face of the disk and water eight or ten degrees warmer across the other 

 copper face. The water delivery of one stream was measured, and its 

 change of temperature between entering and leaving the vessel con- 

 taining the disk was determined by means of two copper and German 

 silver thermo-electric junctions. 



The apparatus containing the disk was surrounded by a water jacket 

 having a temperature near that of the disk, so that the radiation to or 

 from the exposed convex surface of the disk could be neglected. 



This hasty review shows that, if all the measurements indicated were 

 correctly made, the thermal conductivity could be found by a simple cal- 

 culation based on the data affoi-ded by the experiments. In fact, the 

 experiments described in the article under discussion left something to 

 )e desired ; for they showed that different parts of the same face of the 

 lisk were not at the same temperature, and the process of calculation 

 necessary to deduce from the observations the mean difference of tem- 

 perature of the two faces of the disk was laborious, and perhaps to the 

 casual reader not entirely convincing. This difficulty and the desira- 

 bility of certain changes in the apparatus used were recognized in the 

 article itself. 



* E. H. Hall, These Proceedings, Vol. XXXI. p. 271, 1896. 



