84 Barrett, Brown & Haprretp— On the Electrical Conductivity and 
Silicon, like carbon and aluminium, has a powerful effect in reducing the con- 
ductivity of iron. ‘The composition of the two specimens above-named is fairly 
uniform, except for the added silicon. Between 25 to 53 per cent. of silicon, an 
increase of 7-7 microhms is produced in the electric resistance of the alloy for 
every 1 per cent. of added silicon; between 0 and 24 per cent., the rate of increase 
is 11 microhms (see p. 89 and bottom of p. 94). 
Group 7.—CxHRomiuM STEELs. 
Marks. Percentage Composition. Conductivity Copper = 100. Specific resistance (calculated). 
| Cr | C Unann. Ann. Unann. Ann. 
| | 
993 2:00 | 0-90 — wil — 24-2 
Nee I | 3°20 0°45 | 4°8 6-9 35°55 | 24:9 
» A | OD | OD 4:0 4:5 43°45 38-2 
The effect of added chromium in reducing the conductivity of iron appears 
to be nearly the same as that produced by nickel. Unfortunately the carbon as well 
as the chromium differs in the specimens tested, so the true effect of an increase 
of chromium in the alloy is doubtful. The large amount of carbon in the first 
and last specimens augments their resistance ; nevertheless, even in this imperfect 
comparison, an increase of only 1:8 microhms for every 1 per cent. of added 
chromium is shown, @.e. for rich chromium steels: the rate of increase, as in other 
cases, is higher in alloys containing less chromium (see p. 88). 
Copper Steels. 
The last group in Class I. consists of alloys of iron and copper ; of these, three 
specimens were tested. Other specimens of steels containing copper, along with 
one or more metals, will be found in Classes II. and III.; one of these, 1149 A, 
containing, besides copper, one per cent. of aluminium, is repeated here. 
Group 8.——Coprer STEELS. 
Marks. Percentage Composition. Conductivity Copper = 100. | Specific resistance (calculated). 
CG | oc | wm Unann. Anny |) Unann’ | Aan, 
1264 A 1 | O68 0°36 8-7 iio 19°8 14:9 
tea 2°50 0:59 0°32 9:0 11-9 19-0 14:4 
1263 C 2°87 0-17 1:04 8:0 9:8 21:5 17-4 
1149 A* S718 | 0:04 0-16 6:9 8:1 24:9 | 21:0 
* 1149 A has also one per cent. of aluminium. 
