CHEMISTRY: E. D. CAMPBELL 
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nese, five nickle steels, chrom-steel, chrom-tungsten and chrom-molyb- 
denum steel, most of the carbon and a considerable proportion of the 
sulphur may be removed by heating bars of the metal in a slow stream 
of moist hydrogen, the temperature being maintained for from four 
to twelve days between 950°C. and 1000°C. Since the elements other 
than carbon and sulphur are not affected by hydrogen, this method of 
treatment affords a very satisfactory means of changing the carbide 
concentration without material change in composition, since the per- 
cent of sulphur is usually quite low in commercial steels. 
The experimental data given in the second paper, ''The Solution 
Theory of Steel and the Influence of Changes in Carbide Concentration 
on the Electrical Resistivity" demonstrate clearly that Benidicks' Law,^ 
"Equiatomic concentrations in iron possess equal resistivities," is not 
tenable. It is the molecular, not the atomic concentration in metallic 
solutions, which determines the electrical resistivity, just as it is the 
molecular and not the atomic concentration which determines con- 
ductivity in aqueous solutions. 
The fallacy contained in the conclusion drawn by Le ChateHer^ that 
chromium, tungsten and molybdenum have but slight influence on the 
electrical resistance of steel, may be explained by the fact that when these 
elements are present in steel, they form with carbon complex carbides, 
so that the molecular concentration of the carbides is little if any greater 
than if chromium, tungsten and molybdenum were absent. If, however, 
the carbon is removed, the chromium, tungsten or molybdenum will 
itself combine with or dissolve in the iron, each thus producing an in- 
crease in electrical resistivity nearly equal to that which would be pro- 
duced by an equal atomic concentration of carbon alone. 
The force-field theory of solution developed by E. C. C. Baly^ by a 
series of investigations of the action of light on aqueous solutions, may 
be applied to solid solutions in metals and, assuming the unity of mechl 
anism of these and of aqueous solutions, can be made to give a rationa- 
explanation for thermal and electrical resistivity, as well as for the ther- 
mo-electromotive properties of solutes in soHd solutions. 
Many other properties of solid solutions will also probably be found 
capable of explanation by the force-field theory. 
^ On the Relationship of Structure, Density and Chemical Composition of Steel, Amer. 
Chemist, 7, Nov. 1876, (175-178). 
2 Campbell, E. D., Amer. Chem. J., 18, 1896, (719-723). 
3 Zs. physik. Chem., 40, 1902, (545). 
* Le Chatelier, Faris, C. R. Acad. ScL, 126, 1898, (1709, 1782). 
6 Baly, E. C. C, /. Amer. Chem. Soc., Easton, Pa., 37, 1915, (979). 
