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Updated: June 7, 2025
If the manganese, as in slags, be combined with silica, it is frequently necessary first to fuse the specimen with soda.
Of ferromanganese and other very manganiferous substances, in which the manganese need not be determined with greater exactness than to 0.1 per cent., only 0.01 gram. is taken for a test; but of common pig, wrought iron, steel, iron ore, slags, etc., there is taken 0.5 to 1 gramme according to the supposed content of manganese and the desired exactness of the estimation.
In the Heroult process the impurities of the molten iron are washed out by treatment with suitable slags. The furnace consists of a crucible in the form of a closed shallow iron tank, thickly lined with dolomite and magnazite brick, with a hearth of crushed dolomite.
By any of these other methods very philosophical they are, I admit we could not accomplish this. The slags would all contain more or less metal; and when I inform you, that we can afford to remelt those slags if they contain only a half per cent. of copper, you will perhaps understand our reasons for still adhering to our venerable system.
"You must be aware," continued Cosmo, addressing them particularly, "that it has been demonstrated that the continents and the great mountain ranges are buoyed up, and, as it were, are floating somewhat like slags on the internal magma. The mean density of the crust is less under the land and the mountains than under the old sea-beds. This is especially true of the Himalayan region.
The aggregates of globular bodies seen in the section so greatly resemble the globulites of slags and natural glasses, and in their arrangement so forcibly recall the structures seen in the well known pitchstone of Corriegills in Arran, that one is tempted to regard them as indicating the beginnings of the development of crystalline structure in the tabasheer.
As these bubbles have been sometimes lengthened by the flow of the lava before it finally cooled, the contents of such cavities have the form of almonds. In some of the amygdaloidal traps of Scotland, where the nodules have decomposed, the empty cells are seen to have a glazed or vitreous coating, and in this respect exactly resemble scoriaceous lavas, or the slags of furnaces.
So hard, solid, and indurated do these slags, in process of time, become, that a very tall chimney, the most conspicuous object in the works, is built on the top of a slag-bank. And this beautiful commodity is not without its use in the arts.
The greater number consisted merely of a ring of red scoriae or slags cemented together: and their height above the plain of lava was not more than from fifty to a hundred feet: none had been very lately active.
The slags front silver refineries, and even from smelting houses of the coarser metals, have not unfrequently yielded to a second operator a better return than the first had derived from dealing with the natural ore; and the saving of lead carried off in the smoke of furnaces has, of itself, given a large profit on the capital invested in the works.
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