84 



Barrett, Brown & Hadfield — 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 2| to 5^ 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 and 2^ per cent., the rate of increase 

 is 11 microhms (see p. 89 and bottom of p. 94). 



Group 7. — Chromium Steels. 



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, i.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. — Copper Steels. 



* 1149 A has also oue per cent, of aluminium. 



