Experimental values for the solubility of carbon in nickel in the range 700°C to 1300°C yield the equation lnS=2.480−4,880/T, where S is the solubility in grams of carbon per 100 grams of nickel. Values obtained for the diffusion coefficient in the same range fit the equation lnD=0.909−20,200/T, where D is in cm2 per second. These results are of some interest in the problem of the activation of thermionic oxide coated cathodes, and the experimental method used to measure the diffusion coefficients is related to phenomena occurring in vacuum tubes. To extend the usefulness of the results in this direction, rates of reaction between diffused carbon and barium oxide coatings on nickel have been measured. It was found that the rates are diffusion limited over a wide range of conditions of interest.

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HE importance of the determination of gases in metals isshown by numerous papers on this subject. Among those who have pioneered in this field are Oberhoffer (#) and associates in Aachen, Germany, and Jordan and Eckman (1) and others at the National Bureau of Standards in the United States. Numerous additional papers have appeared in which the authors have recognized the importance of furnace design; each in turn has made contributions, but they have been more or less guided by the furnaces described by those who pioneered in this field. In many cases, it'has been necessary in this laboratory to carry out analyses on a small quantity of material, and, in view of this, the authors of this paper have made radical changes in furnace design which provide data of maximum precision and reliability. The details of this furnace are shown in Figure 1.In general, the furnace consists of a glass envelope, a suspended clear quartz tube, and a graphite crucible. The envelope is made of Corning 774 Pyrex and has a removable ground-glass joint at the bottom. This joint is made vacuum-tight by applying a thin coat of sealing wax to the ground surface. The joint is assembled by inserting the wax-coated plug into the female section section. The outer glass surface is then heated with a Bunsen burner and the plug is rotated with pressure until properly seated.