92 



Barrett, Brown & Hadfield — On the Electrical Conductivity and 



The carbon is high in all these specimens. In the first three specimens 

 the percentages of manganese and of carbon remain about the same, the amount 

 of chromium in each differing ; the conductivity it will be seen is very low 

 in all. 



From the chemical analysis we should expect to find tlie conductivity of 

 1274 A higher than that of 1430, but the reverse is the case, confirmed after 

 several trials. This is, no doubt, due to the difference in hardness, as the latter 

 is distinctly softer to the file than the former. 



Annealing makes a great difference in the conductivity of these manganese 

 chromium steels, e.g. 1430 in the unannealed state had a conductivity of 3*4, 

 whilst in the annealed state it was 4-7, taking copper as 100. This difference 

 is still more striking in the magnetic permeability of this specimen in the two 

 states (see p. 114). The alloy, 1233 A, is enormously hard, and can hardly be 

 touched by a file. 



The next is a series of manganese-tungsten steels. 



Group 14. — Manganese-Tungsten Steels. 



Tungsten, it will be remembered, had the least effect of any element, so 

 far tried, in reducing the conductivity of steel; the addition of manganese to 

 the tungsten steels produces a great drop in the conductivity, as will be seen 

 by comparing 687 above, with 1294 H in Group 4. Compare also the man- 

 ganese steel 53 in Group 2 with the specimen 687, haviiig the same quantity 

 of manganese and carbon ; the effect of Z\ per cent, of tungsten added to the 

 latter raises the conductivity when both specimens are annealed. The same 

 remarkable increase in conductivity will be seen by comparing 683 witli 1381 in 

 Group 2, Series B ; in the former 10 per cent, of tungsten has been added to a 

 manganese steel. Note also the effect of practically reversing tlie amounts of 

 tungsten and manganese in the specimens 683 and 1343. 



The next group exhibits the effect of adding silicon to manganese steel. 



