/,v.s/x/ ////// mused ly Alloying Iron with Various Element*. 48:> 



selecting that specimen of iron which has about the same carbon or 

 other impurity as that contained in the particular alloy and subtracting 

 the resistance of the iron. The result is shown in the next table. 



Table I. Approximate Increase in Electric Resistivity (in microhms 

 per c.c. at 18 C.) of Annealed Iron Alloys produced by adding 

 to Iron Different Percentages of the Elements named in the first 

 column. 



Percentage of added element. 

 Allovs of iron , * . 



with 2 per cent. 3 per cent. 5 per cent. 



Tungsten 4*0 5-0 6*0 microhms 



Nickel 7-0 l>-0 13-0 



Chromium 10 -0 11- 5 14-0 



Manganese 16-0 18-0 24-5 



Silicon 2G-0 ;U'0 49-0 



Aluminium 2S'0 36'0 54'0 



Dividing these values by the percentage at the head of each column, 

 it will be seen that as the alloy becomes richer in the added element 

 the increase of electric resistivity becomes less and less for every <>nr per 

 cent, of the element added. The comparative effect of carbon is difficult 

 to ascertain owing to various causes, (") the impossibility of making 

 homogeneous alloys of iron with large percentages of carbon, the 

 highest carbon in our specimens being 1 } per cent. ; (It) the different 

 conditions in which the carbon may exist in the alloy ; and (<} the 

 difficulty of excluding impurities such as manganese and silicon, 

 minute amounts of which exert a serious effect on the conductivity. 

 However, by comparing the conductivity of alloys of iron having nearly 

 similar quantities of Si and Mn, but containing different quantities 

 of carbon, a close approximation of the effect of this element on the 

 conductivity of iron is arrived at. The result shows that the increase 

 of one-tenth of one per cent, of carbon in iron containing 0*03 carbon 

 causes an increase in the specific resistance of nearly 2 microhms per 

 c.c., but when the carbon is raised from 0'13 to 1*13 the increase in 

 specific resistance is at the rate of 5 microhms for 1 per cent, of added 

 carl on, about one-fourth of the rate of increase at the smaller per- 

 centages. The position of carbon on Table I therefore appears to lie 

 near to chromium. From specimens of two impure alloys containing 

 cobalt with iron, the increase of resistance produced by cobalt was 

 estimated to be somewhat less than nickel but greater than tungsten ; 

 its position in Table I would therefore appear to lie near to nickel. 



If now we compare the increase of resistance in iron produced by 

 alloying it with these elements, with the atomic weights of the added 

 elements, we find, as a rule, that those elements with the highest 



VOL. LXIX. 2 M 



