74 



Barrett, Brown & Hadfield — On the Electrical Conductivity and 



manganese impurity.* The specimens 1392 I, B and A, are almost alike in 

 the percentage of carbon they contain, the difference in conductivity being due 

 to the differences in the quantity of silicon and manganese present. It will be 

 noticed that annealing in all cases increases the conductivity. The next 

 series (B) are less pure carbon steels, and have a lower order of conductivity. 



Carbon Steels (Series B). 



The result of analysis shows that manganese, and, as a rule, silicon, are 

 present in not inconsiderable quantities in these specimens, so that they may be 

 regarded as low manganese steels. 



The foregoing results are plotted in the accompanying curves, fig. 2, where 

 percentages of carbon ai-e taken as abscissae, and conductivity as ordinates.f The 

 departures from the smooth curve which is drawn are not very great, and would 

 doubtless disappear if the specimens were of uniform purity, with the exception 

 of the added carbon. In fact an approximate estimate of tlie quantity of carbon 

 in any specimen of carbon steel might be quickly obtained by a determination of 

 the electric conductivity of the particular sample, provided the other constituents, 

 especially the silicon and manganese, were practically uniform throughout the 

 specimens. On the other hand, from the electrical conductivity of samples of 

 steel, in which the percentage of carbon only is known, we can infer the purity or 

 otherwise of the samples, and can arrange them into series of high or low-class 

 steels. As a matter of fact this was done in the above specimens, when only the 

 amount of carbon present was known ; and the division into series A and B was 

 fully justified when we received the full analysis. 



It will be interesting to compare the increase of resistance for each one per 

 cent, of the added element in these and the other steels in Class I. In every 

 case the compai-ison will be made of the specimens in the annealed state. 



The first four specimens in Series A show that an increased re.sistance of 



* The conductivity of 1392 L is a little higher than its composition 'would indicate. There is prohably 

 a slight error here in the chemical analysis of this alloy. 



f A slight corrrection needs to be made in the lower part of series A curve, which should be a little 

 lower than shown, as by mistake this part of the curve was plotted from some annealed specimens, the rest 

 of the curves, both in series A and B, being taken from the unannealed rods. 



