﻿282 



Bar us and Strouhal — Hydro-electric 



electrode,* the former must be positive with respect to the 

 other ; that the phenomena in hand are mere effects of polariza- 

 tion. In other words, it is permissible to assume that the con- 

 tinuous variation of the mechanical texture of steel produced 

 by annealing is the cause of corresponding variations of the 

 rate of deposition of hydrogen on the submerged metal ; that 

 the electromotive forces observed are expressions of this hydro- 

 gen polarization, and bear no immediate relation to the electro- 

 chemical character of the steel electrode at all. 



On the other hand, the dependence of the hydro-electric 

 positionf of steel, caeteris paribus, on the amount of free carbon 

 contained is sufficiently obvious to conflict with this view. It 

 is expedient to insert here a tabular comparison of the data 

 under consideration. In the table, c denotes the number of 

 grams of free carbon per gram of steel ; e and e' the differences 

 of potential between steel tempered and steel hard when plunged 

 in zinc sulphate and in water respectively. A is the density, s 

 the specific resistance, a the resistance-temperature coefficient, 

 h the thermo-electric hardness of wires of the same kind of steel 

 (Stubs' best), a and h are obtained by calculation. 







Diameter 2p= 



= 0-081 cm . 









Annealed 

 from hard at 



c 



e 



e' 



A 



s 



a 



h 



20°, oo 



o-oooi 



o-ooo 



o-ooo 



7-6547 



439 



0-0017 



18-1 



100°, l 11 















7-6666 



39-3 



18 



16-2 



100°, 13 h 



0-0005 



0-006 



0-020 



7 6745 



35-5 



20 



14-6 



190°, l h 















7-6841 



30-8 



23 



12-7 



190°, 5 h 



0-0007 



0-020 



0-027 



7-6828 



27-1 



27 



11-2 



350°, .. 



0-0017 



0-033 



0-089 



7-6806 



20-7 



33 



8-5 



450°, l h 



0-0009 



0-038 



105 



7-7190 



18-4 



36 



7-6 



530° 







.... 







7-7227 



18-2 



36 



7-5 



690° 









_ . . _ 



7-7272 



17-2 



38 



7-1 



310° 



.... 











7-7586 



17-6 



37 



(7-3) 



1000° 



0-0040 



0-057 



0-185 



77705 



186 



37 



(7-7) 



Commercial. 



0-0053 







0-252 



7-7268 



163 



0-0039 



6-7 



When steel of a given kind is operated upon and total carbon 

 therefore a fixed quantity, the variable c affords a comparatively 

 convenient means for detecting the presence and amount of 

 chemical change; but it is highly probable that a clearer 

 insight into the nature of the decomposition of carbide produced 

 by annealing hard steel would be obtainable from a study of 

 the character and quantity of the hydrocarbons (gaseous, liquid) 

 volatilized during solution. They accumulate in < copious 



* Hydrogen accumulates visibly on the + electrode when immersed in zinc 

 sulphate. 



f Curiously enough the observed points c and e' lie nearly on a right line. 



