94 



Barkett, Brown & Hadfikld — On the Electrical Conductivity and 



Comparing 1178 B with 1167 D in Group 5, which has the same amomit of 

 akiminium, it will be seen that the addition of 1*75 per cent, of chromium 

 reduces the conductivity only 20 per cent. The greater effect produced by 

 aluminium than by chromium in lowering conductivity is seen by comparing 1179 B 

 and 1 178 D. The specimens marked 1178 are similar chromium steels to which 

 varying amounts of aluminium have been added. The increase of resistance 

 thereby produced is very marked, between 1178B and 1178 E the resistance 

 increases at the rate of 11 microhms for 1 per cent, of aluminium added to 

 these chromium steels, practically the same increase produced by the aluminium 

 as when the chromium was absent (see p. 83). This rate is taken between 

 0-75 and 4-5 per cent, of added aluminium ; between and 1 per cent, the rate of 

 increase of resistance is still higher, as might be expected. By comparing the 

 resistances of the aluminium steels in Group 5, p. 83, with each other, and with a 

 corresponding carbon steel without aluminium, the rate of increase of resistance for 

 1 per cent, of aluminium added to iron will be found almost the same as the rate 

 deduced from these composite steels. The following table shows these results : — 



The next group shows the effect of adding silicon to chromium steels. 



Group 18. — Chromium-Silicon Steels. 



The enormous increase in resistance due to silicon is seen by comparing 

 517 and .518; also by referring to 11771 in Group 7, a similar chromium steel 

 toll85F, but without the silicon. This comparison shows that the rate of 

 increase for each 1 per cent, of added silicon is 16 microhms between 1 and 1-8 

 per cent, of silicon, and 11 microhms between and 2 '25 per cent, of silicon. 



