The Ketchikan miner., 1909-03-27

to certain extent by the earth, oxides, lime etc., in order t reduce the specific weight of th, slag sufficiently to allow the metalli, particles to sink and collect. Taking a slag, for instance, consisting of 3t per cent silica, 10 per cent ferrous oxide and 20 per cent lime, the later might be partly replaced by mag anesia, alumina, etc., Tn various pro- portions, and their amount total may also be diminished necessitating an increase of iron at the same time, but it would not he safe to go below a certain limit, about 10 per cent be- cause the slag would become too heavy. The ideal self-fluxing ore, therefore, would be an ore containing tbe acid and basic constituents in sucn pro- portion as required to make good slag and which could be smelted with out adding any tluXes. Such an ore is seldom found in practice; the metal lurgist is content with an ore requir- ing huxes that can be cheaply procured and which is free from impurities in- terfering with the smeltng. Such must be named arsenic and antimony, heavy spar, galena and, worst of all, zinc, which becomes prohibitive ii exceeding about 10 per cent of the charge
 1 According to the character of the ore, we distinguish between the smelt- ing of oxidized ores. intending to produce metallic copper directly, and the smelting of the sulphide ore, pro- ducing an intermediate product, matte. 1 Oxidized ores are not as common as the sulphides; they are usually con- fined to the upper part of a vein and the probability of changing into the latter at a certain depth, usually be- low the water level, must be taken into consideration when the erection of shelter is planned.
 By far the greater part of the cop per produced is obtaired from the sulphldes. not in metallic form, but as mixture of sulphides, called matte. By making this product it is possible to smelt ores that contain per cent copper or even less and obtain a matte rich enough (45 pei cent or over) to extract the metal by different process. Matte smeltinp l is really dry concentration, by wi ic ! the silica and the earthly constituents of the ore and part of the excess oi sulphur and iron are removed, con- densng the copper contents into a smaller bulk in various proportions. at ratio of from }, 10, or even 20 i into one. There are two ways 10 ac- conpiish this object, the old method of matte smelling, in which part ot the sulphur is removed by preimi- nary roasting and the residue slnelted with the addition of fuxes and fuel. and the later method, called pyritic smelting. In this method there + smelted without roasting. utilizing the heat from the burning sulphur, adding only very small percentage of carbonaceous fuel. It is evident from the foregoing brief description of the principles of smelting that 8 definition of what constitutes a gooo smelling ore which can only be given in general way; it is an ore which l. free from injurious minerals and con- tains silica and the bases in propor- tion required for a good slag. without the addition of either one of them, as Aux. Whether certain ore can bt smelted with profit in a given place depends to such an extent on local conditions that the problem has to be solved for every particular case. The smelling of copper today is such ar exact science that every result can be calculated in advance. and there is nc longer any excuse or failure in an en- terprise of this kind.