Magnetic Permeability of various Alloys of Lron. 99 
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.—CxHrRomiumM-CoprEr STEEL. 
Mark. Percentage Composition. | Conductivity Copper = 100. | Specific resistance (calculated). 
Cr Cu | C Unann. | Ann. Unann. Ann. 
1255 A 5°75 1:8 | 0°85 41) 55 42°7 81:2 
Group 20.—CuHromium-Tunesten STEEL. 
Mark. Percentage Composition. | Conductivity Copper = 100. | Specific resistance (calculated). | 
| i 
! : : 
Cr W | C | Unann. | Ann. Unann. Ann. 
| | 
1189B 0-75 2:0 | 0:25 | 766 9:6 I 2205 179 | 
Whilst the addition of small percentages of copper and tungsten do not 
much affect the conductivity of chromium-steel, it will 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 1167 D in Group 5. 
Group 21.—Atumrintum-Coprer STEEL. 
Mark. Percentage Composition. | Conductivity Copper = 100. Specific resistance (calculated). 
Al Cu C Unann. | Ann. | Unann. Ann. 
| 25:0 21:0 
1149 A 1-0 3°75 0:04 6°9 | 81 
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.—Atuminium Siiicon STEEL. 
Mark. Percentage Composition. | Conductivity Copper = 100. | Specific resistance (calculated). 
| | ie) 
Al Si C | Unann. Ann. Unann. Ann. 
803 0°5 2°25 0°67 | 3°54 4:0 48°6 43°0 
