OUR attention was early directed to the utilization of this heat as an important waste product from smelting operations. Of all purposes to which heat could be applied, that of the production of steam appeared to us the most directly useful and possible, and our experiments have therefore been conducted with that object. As the subject-in common with almost all mining and metallurgical problems-partakes more of the nature of an economical than a purely scientific problem, it will be necessary in this paper to deal somewhat more with the economical aspects of the subject than with the purely scientific. A series of careful measurements was first undertaken with slags produced from silver-lead smelting furnaces at Broken Hill, with a view of determining the true values of the heat wasted in the slags ; and the results as given below show that although a comparatively small proportion only of the total heat produced by the combustion of the coke supplied to the furnaces is contained in the slags (the remainder being bound in the chemical reactions of the ores and fluxes in the furnace or passing up the flues with the gases) the amount is still large enough to be of very considerable importance, and its utilization for steaming purposes capable of effecting an important economy. The following are the principal data determined by the measurements referred to :-Specific gravity, 3.8 ; temperature of exit from furnace (average), 2,000 degrees Fahrenheit ; specific heat, 25 ; latent heat per pound (probably), 120 heat units. Total heat per pound, 620 heat units. Average output of slag from one furnace 112in x 60in, 4,400 pounds per hour. Theoretical mechanical equivalent of slag from one furnace, 1,064 horse power.