THERMAL CONDUCTIVITY AND SPECIFIC HEAT OF MANGANESE-STEEL. 949 



tibility is about 8 ^ 00 of that of iron, i.e., only fractionally greater than that of copper, 

 brass, or air ; further, that it is constant ; not undergoing any change corresponding to 

 the " breakdown " in resistance to magnetisation which is found in the case of iron. 



From the experiments of various observers, it would seem that the electrical resistance 

 of manganese-steel is about eight times that of iron, the temperature coefficient being one- 

 third of that in iron. 



Thermal Conductivity of Manganese-Steel. 



Experimental Methods and Details. — The bars upon which were made the experi- 

 ments for the determination of the conductivity were kindly furnished, in the rough cast 

 state, by Messrs Hadfield. The work of bringing them into the required shape and 

 dimensions was one of considerable difficulty. It was at first attempted to reduce them 

 to the desired rectangular section by planing, but this was found to be simply impossible. 

 To begin with, only thick shavings could be taken off at each stroke of the planing-tool, 

 which, when it did get a good grip, seemed rather to tear than to cut the material. 

 Again, the planing-tool s were soon all ruined, for, after a few minutes' work, their edges 

 were all but completely turned off. Thus, even with the best tempering of the tools 

 possible, the process of planing was found to be useless. In this extremity, Messrs 

 Hadfield were asked to supply a piece of manganese -steel of harder quality than that 

 of the bar, with which to make a planing-tool, but in reply they stated that although 

 this had been frequently suggested, it had not proved successful. In these circumstances 

 recourse was made to grinding the bar down by means of an emery-wheel revolving at 

 high speed. This method does not, of course, ensure the same uniformity of section that 

 planing would do ; but on testing very carefully the finished bar, it was found that 

 the section was quite uniform enough for the purposes of the experiment. The dimen- 

 sions of the long bar were 50^ inches by 1^ inch by 1^ inch. Eight holes were drilled in 

 this bar for the thermometers, the first being 9 inches from one end, the others 12, 

 15, 18, 24, 30, and 42 inches respectively from the same end. The holes were 1-g- inch 

 in depth and ^ inch in diameter. The length of the short bar was 20 inches, its cross 

 section being, of course, the same as that of the long bar. One hole of the same size as 

 the above was drilled in the short bar, which was fitted with screw-eyes at the ends with 

 which to support it on bearings while being heated. Both bars were finally nickel-plated. 



A sample of the turnings from the bar was analysed in Professor Crum Brown's 

 laboratory ; the following is the mean of two determinations : — 



Iron, ....... 87"56 per cent. 



Manganese, ...... 9'89 „ 



Carbon, . . . . . 1'30 „ 



Silicon, 0-48 



The method of finding the conductivity was substantially that originally devised by 

 Forbes, the only difference being that a shorter bar was used, with a cooling bath placed 



