Sound velocities, densities, and lattice parameters of hot‐pressed bodies of the solid‐solution series Al2O3−Cr2O3 were investigated. Measured lattice parameters deviated slightly from Vegard's law. The compositional dependence of the longitudinal sound velocity agreed well with the predictions of Birch; the observed dependence of the bulk modulus on ionic volume did not agree with the relation of Anderson and Nafe.

The flow properties of six monodisperse kaolinite fractions were studied over a large range of concentration. From these results, it has heen possible to set up an equation relating viscosity to concentration which holds over a very wide range. Equations relating concentration to thixotropy and to the yield point which have general application could also be established. The viscosity of a suspension is obtained from the sum of three quantities, namely, those contributed by (1) the liquid, (2) the individual particle, and (3) the collisions of the particles. Thivotropy is found to be due to the sum of two quantities, namely, the contribution of (1) the individual particle and (2) the interference of the particles. The yield point in these fractions was found to be proportional to the cube of the concentration. With these relations, it is possible to calculate the viscosity of a casting slip for any change in specific gravity.

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gm. per ml., which is 3.4% higher than the average measured density of 3.24 gm. per ml.The microstructure of the cermet (Fig. 7) indicates the presence of two phases, a gray area whichis the boron-carbide matrix and a white area which is the metallic phase (black areas are believed to be pores). As previously stated, the iron addition was approximately 15 volume % of the body. This photograph, which depicts an area representative of the cermets evaluated, shows that considerably more than 15% of the bonding material is present. This disparity is the result of solution or reaction of the boron carbide with the iron, as indicated by the bonding experiments.The measured values of density of hot-pressed boron carbide listcd in Table I1 are very close to that of single crystal of boron carbide, which is 2.fi2 gm. per mL5 IV. Summary of ResultsProm a qualitative investigation of boron carbide with nickel, cobalt, iron, or chromium, a method was found to facilitate sLudy of the bonding of a metal and a ceramic material by exposing the metal in intimate contact with a ce-6 H. K. Clark and J. L. Hoard, "Crystal Structure of Boron Carbide," Jour. Amer. Chem. Soc., 65 [ l l ] 2115-19 (1943); Cernm. Abslracls, 23 [S] 133 (1944).A series of glasses in the system Na20-SiOzTiOz were melted. Density measurements and refractive indices were determined. Molar refractions of the various glasses were calculated using the Lorentz-Lorenz relationship. The partial molar refraction of TiOz, as determined in glass, corresponds closely with the values obtained from crystalline compounds and indicates that the Ti4+ ion exists in sixfold coordination. Interionic distances were calculated using the Kordes equation, the calculated Si-0 distance being 1.60 8.11. and the Ti-0 distance, equal to 2.01 8.u.