74 Barrett, Brown & Haprirtp—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), 
| Marks. Percentage Composition. Conductivity Copper = 100. | Specific resistance (calculated). | 
| } 
| C Si Mn Unann. Ann. Unann. Ann. 
| 611 0:58 0-49 0:58 75 8-0 23°1 21:5 | 
6138 1:00 . op 6°8 CU 25°2 22°3 
614 1:25 0:46 0°62 6°5 7:3 26°6 23°6 
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 are taken as abscissze, and conductivity as ordinates.t 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 the 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 comparison will be made of the specimens in the annealed state. 
The jst four specimens in Series A show that an increased resistance of 
* The conductivity of 1892 L is a little higher than its composition would indicate. There is probably 
a slight error here in the chemical analysis of this alloy. 
+ 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. 
