Magnetic Permeability of various Alloys of Iron. 



95 



The two next specimens show the effect of adding first copper and then 

 tungsten to chromium steel ; whilst the effect of the addition of both copper and 

 tungsten to a chromium steel is given in Group 25. 



Group 19. — Chromium-Copper Steel. 



Whilst the addition of small percentages of copper and tungsten do not 

 much affect the conductivity of chromium-steel, it vpill be seen by comparing 

 1264 A in Group 8 with 1255 A in Group 19, that the addition of chromium to 

 a copper steel largely reduces its conductivity. 



The effect of adding 3-75 per cent, of copper to a low aluminium steel 

 has practically no effect in altering the conductivity, as will be seen by comparing 

 the next specimen with 1167D in Group 5. 



Group 21. — Aluminium-Copper Steel. 



On the other hand, the addition of 2-25 per cent, of silicon doubles the 

 resistance of a low aluminium steel, as seen by comparing 1167 D, p. 83, 

 with 803 below. 



Group 22. — Aluminium Silicon Steel. 



