is plotted against P/Po, according to equation (1). This plot should yield a straight line usually in the approximate relative pressure range 0.05 to 0.3. The data are considered acceptable if the correlation coefficient, r, of the linear regression is not less than 0.9975; that is, r2 is not less than 0.995. From the resulting linear plot, the slope, which is equal to (C 1)/VmC, and the intercept, which is equal to 1/VmC, are evaluated by linear regression analysis. From these values, Vm is calculated as 1/(slope + intercept), while C is calculated as (slope/intercept) + 1. From the value of Vm so determined, the specific surface area, S, in m2·g1, is calculated by the equation:
A minimum of three data points is required. Additional measurements may be carried out especially when nonlinearity is obtained at a P/Po value close to 0.3. Because nonlinearity is often obtained at a P/Po value below 0.05, values in this region are not recommended. The test for linearity, the treatment of the data, and the calculation of the specific surface area of the sample are described above.