president's address — SECTION B. 125 



oxidation and slag-formation is generally lower in sulphur than the 

 protosulphide. The whole action is self-directive or autonomous. 

 The silica remains chemically inert from the top down to the oxidation 

 zone, and also below that zone, though exceedingly active within it. 

 At the same time it is physically, i.e., mechanically, of the utmost 

 importance in these other levels through building up a honeycombed 

 or vesicular aggregate, in the interstices of which the molten sulphide, 

 blast-borne, trickles slowly down against the upcoming gases. In the 

 " laboratory " proper, roughly in the centre of this porous structure, 

 the mutual assimilation of the silicious pieces and the oxidising sulphide 

 corrosively destroys the individuality of both ; but, on the one hand, 

 there is a contraction of mass by the union of silica and protoxide for 

 the formation of slag, and, on the other, an explosive expansion of the 

 gas volume due to the sudden elevation of temperature engendered 

 by the combustion of the iron and the sulphur, assisted by the slag- 

 formation. The condition of porosity is thus practically preserved in 

 this particular spot by the action going on there, while it is the duty 

 of the metallurgist to see that it is suitably maintained elsewhere in 

 the furnace shaft. The furnace must be kept properly open, both 

 above and below the fiery nucleus. In fact, it may truly be said that 

 the proper maintenance of this purely mechanical feature is one of the 

 principal secrets to success. In distinction from an opportune coke- 

 bed for the charges to rest on in their descent, there is only this silica 

 skeleton to rely on for a proper furnace movement, and the situation 

 is one far removed from a " bed of roses." " Eternal vigilance " is 

 indeed required, and liberty from freeze-ups — and a minimum coke 

 bill — can be secured for no other price. 



The special slag composition which falls is wholly subject to the 

 self-governing relations which happen to be established between the 

 air blown in and the iron sulphide and silica. The presence of coke and 

 limestone, or other substances yielding chemical bases, affects the 

 result, but we can only consider the general features. The general 

 tendency of the furnace conditions, as at Mount Lyell, for instance, 

 is to form a singulo-silicate, identically a? in the converter vessel. 

 The introduction of heat from an extraneous source, such as through 

 a heated blast, or by an addition of coke sufficient to live down to the 

 oxidation zone, raises the acidity of the slag, but also decreases the 

 calories developed by the sulphide, relieving and interfering with the 

 work of oxidation. The matte then leaving the furnace is greater in 

 quantity and lower in tenor than in the opposite case. The matte 

 formed is obviously only that part of the particular sulphide supporting 

 the action in the oxidation nucleus which happens to be in excess of the 

 influence of the blast. The copper, for its part, may be regarded as 

 practically inert throughout the whole furnace-action, and simply goes 

 through the furnace under cover of the protection of the iron sulphide 



Given a set adjustment of matter and force within the furnace, 

 tending towards a certain slag composition, the latter cannot be varied 

 by decreasing or increasing the amount of free silica on charge. It 

 is true that this substance constitutes the direct available means for 

 raising or lowering the degree of concentration of ore into matte. 



