WHEN the Australasian Institute of Mining Engineers visited Broken Hill-eleven years ago-it was freely acknowledged that the immense tailings dumps, with their vast stores of metals, presented a problem in metallurgy for which there was then no satisfactory solution. The local history of the past decade, however, furnishes another example of the great progress made in recent years in metallurgical practice, and members of the Institute may be congratulated on the development in this part of Australia of methods of concentration which are destined to become of world-wide importance. As illustrating in some measure the lines upon which local practice has developed in recent years, the writer proposes to invite attention to an historical summary of the metallurgical practice of the Sulphide Corporation Ltd. on the Central Mine, dealing particularly with the exploitation of the zinc contents of the ore. The various stages leading up to the introduction of the flotation process will thus be disclosed, and the gradual evolution of that process to its present state of efficiency shown. The writer does not pretend to deal with the strictly scientific side of the question; the causes that produce the phenomena are not touched on. Not that this phase has not received due attention; but our greater concern has been the practical application of the principles governing the various processes that have been put into operation.