68 Barrett, Brown & Had field — On the Electrical Conductivity and 



diameter (No. 5 B. W. G,). Thoy were then cut into uniform lengths of about 

 42 inches (106 cms.) long, and once more heated to 700° C. in order to be 

 straightened. 



In the first instance the rods were all tested for electric conductivity in the 

 state in which they were received, that is ''as rolled" or unannealed, as this is 

 the usual condition under which rods or wires are supplied in commerce. But 

 the effect of rolling in many cases left the rods in a more or less hardened or 

 strained condition, which, as anticipated, was found to affect the electric con- 

 ductivity to some extent, and still more the magnetic permeability. Hence, in 

 order to reduce them all to precisely the same physical state, they were sent 

 back to Sheffield to be annealed, and on their return were all re-tested. 



The annealing was conducted as follows : — The rods were heated in an 

 annealing furnace to a temperature of a white heat (about 1000° C), and allowed 

 to cool down slowly in an east and west position for a period of nearly 100 

 hours, so that the cooling occupied upwards of four days and four nights. 



In order to compare the electric and magnetic properties of the same alloy, 

 after different thermal treatment, a duplicate set of some of the specimens, 

 especially the "nickel steels," were prepared both in the annealed and unannealed 

 states, the latter meaning "as rolled" without further treatment; a third 

 sample of a few specimens were also prepared which were " water-quenched," 

 i.e. the rods were heated to about 1000° C, and plunged into cold water at this 

 white heat. 



Composition of the Speci77iens. 



A chemical analysis of all the specimens was made in the chemical labora- 

 tory attached to the Hecla Steel Works. In some cases an ultimate analysis 

 was undertaken; this would have been desirable in every case, but the 

 labour and time involved in an exhaustive analysis of such an extensive sei'ies 

 was impracticable in the first instance. Except, therefore, where specially 

 mentioned and the details given, the analysis must be taken to indicate the 

 main constituents of the specimens. 



The various alloys of iron, for brevity, though in many cases incorrectly, called 

 " steels," which we have tested, may be divided into three classes : — 

 I. Those consisting of one element added to the iron. 

 II. Those consisting of two added elements. 

 III. Those consisting of three or more elements added to the iron. 



Each of these classes consisted of numerous groups, and each group con- 

 tained from one to a dozen specimens, having different percentages of the added 

 element or elements. After their manufacture a distinctive mark or number was 



