Properties , Specific Resistance, and Hardness of Steel. 359 



Spirals II. and IV. were afterwards softened by heating to 

 redness in a Bunsen burner. Their specific resistance in this 

 condition was found to be (without allowing for the smaller 

 section) 



*IL S =0-154, *IV. S =0-159. 



Finally, in order to compare the results determined with 

 induction-currents with those in which a Smee was employed, 

 certain of the experiments were repeated. The agreement 

 was entirely satisfactory. 



Deductions and Supplementaky Experiments. 



VII. Hardness and Thermoelectric Properties of Steel. 



a. From the data contained in Tables II., III., and VII. 

 we derive that the thermoelectric position of steel progresses 

 continuously with its degree of hardness, or, in other words, 

 thermoelectric and mechanical hardness are direct functions 

 one of another. 



This statement involves the assumption that a rod cannot 

 pass from the glass-hard (maximum) to the soft state (mini- 

 mum) without passing through every intermediate stage — or 

 that, by proper methods of annealing, every state between the 

 maximum and minimum could be produced. This, I dare say, 

 will generally be admitted. 



As of further interest I may add : — (1) that rods cut from 

 the same wire and glasshardened in the same way possess also 

 the same thermoelectric hardness (Table VI.); (2) this is the 

 case even when the rods are carefully rehardened (rods [III]', 

 [V]', Table VI.) ; (3) that if we start from like maxima, the 

 ther mo-cur rent always passes from the less to the more annealed 

 through warm. (The direction of the current was independently 

 observed.) 



b. From an examination of the data obtained from different 

 material, we infer that the T. E. H. of soft and similarly an- 

 nealed rods approximates to the same value*; that the value of 



others were immersed but for two or three minutes. The temperature at 

 which the rods 6 and 7 were annealed could not be determined with cer- 

 tainty, a microscopic air-bubble in the neck of the mercury-reservoir 

 having given rise to a rupture of the thread. 



* In order to compare the degree of hardness corresponding to a parti- 

 cular oxide tint with that corresponding to a particular temperature of 

 the oil-bath, use was made of the Tables to be found in Frick's Physikal. 

 Technik, 3 ed. p. 377; also Wagner, Chem. Tech. 8 ed. p. 29. On the 

 authority of these, 230° corresponds to yellow-, 290° to blue-annealed. 

 We should therefore expect rods 6, 7, and 8, 9 (Table VII.) to agree with 

 rods C and B (Table III.), respectively. This is sufficiently the case. 



2B2 



