uring the development of the flotation process for the recovery of lead and zinc at Broken Hill, New South Wales, a number of mechanically agitated flotation machines have been developed and used in the concentrating plants on this field. Descriptions of these flotation machines can be found in the Proceedings of the Australasian Institute of Mining and Metallurgy* 1 2 3 4 and in the Transactions of the Institution of Mining and Metallurgy (London). These machines were equipped with impellers for mixing the various reagents with the pulp, and aerating it to promote a froth, thus enabling the separation of the sulphide from the gangue minerals. The impeller used in these machines was a 45 blade cruciform type and was developed from that used in the Gabbet mixers of the Cattermole plant at the Central Mine, and described by James Hebbard* and also Walter Broadbridge.