1. Yancey, H. F., Geer, M. R., and Sokaski, M., Paper F1, Third International Coal Preparation Conference, Liège (1958).
2. Meerman, P. G., Second Symposium on Coal Preparation, Leeds, 253 (1957).
3. Whitmore, R. L., Second Symposium on Coal Preparation, Leeds 282 (1957).