. . "omparable materials, or sometimes a mixture mainly comprising a mixture of at least La, Ce, Pr, Nd and Sm, are intimately blended together with pure individual oxides, carbonates or other compounds that form oxides upon heating, of the La and Mn base metals, for example, individual La2 O3 or LaCO3, individual MnO2, or comparable materials, and also with pure individual oxides, carbonates, or other" . .