The ballast consists of such materials as broken stone, furnace slag, gravel, cinders or earth, the lower layers commonly consisting of coarser materials than the top ones, and its purpose is to provide a firm, well-drained foundation in which the sleepers or crossties may be embedded and held in place, and by which the weight of the track and the trains may be distributed over the road-bed.
It was about this time that the first experiments were made (in Germany) with basic slag, a material which had hitherto been regarded as a worthless by-product of steel manufacture.
A year or two later field trials were begun in England, with the final result that basic slag has become recognized as a valuable source of phosphorus for growing crops, and is now in constant demand for application to the soil as a fertilizer.
It is then raked out on the work-stone and divided into a very poor "grey" slag which is put aside, and a richer portion, which goes back into the furnace.
The "browse," after removal of the "grey" slag, is reintroduced, ore added, and, after a quarter of an hour's heating, the mass again placed on the work-stone, &c.
The slag and matte formed float upon the lead in the crucible and are tapped, usually together, at intervals into slag-pots, where the heavy matter settles on the bottom and the light slag on the top. When cold they are readily separated by a blow from a hammer.
For the commoner grades of dark-coloured bottles the glass mixture is cheapened by substituting common salt for part of the sulphate of soda, and by the addition of felspar, granite, granulite, furnace slag and other substances fusible at a high temperature.
When prolonged heating is required at very high temperatures it is found necessary to line the furnace-cavity with alternate layers of magnesia and carbon, taking care that the lamina next to the lime is of magnesia; if this were not done the lime in contact with the carbon crucible would form calcium carbide and would slag down, but magnesia does not yield a carbide in this way.
The material for filling may be the waste from earlier workings stored in the spoil banks at the surface; where there are blast furnaces in the neighbourhood, granulated slag mixed with earth affords excellent packing.
The earth surface above these natural furnaces has been hardened, cracked and sometimes melted into a reddish slag, called scoria, which, on account of its resemblance to lava, has given rise to an incorrect impression that the region was once the centre of volcanic disturbances.
Proctor in 1877 directed attention to the composition of the slag resulting from the burning of esparto, which they found to be strikingly similar to that of average medical bottle glass, the latter yielding on analysis 66.3% of silica and 25.1% of alkalies and alkaline.
Earths, and the slag 64.6 and 2 7.45% of the same respectively.
Other matrices are slag cement, a comparatively recent invention, and some other natural and artificial cements which find occasional advocates.
This they did with the excuse that the new product resembled one class of steel - cast steel - in being free from slag; and, after a period of protest, all acquiesced in calling it " steel," which is now its firmly established name.
Wrought iron is slag-bearing malleable iron, containing so little carbon (0.30% or less), or its equivalent, that it does not harden greatly when cooled suddenly.
Weld steel is slag-bearing iron malleable at least at some one temperature, and containing more than 0.30% of carbon.
The second period, by converting the metal into the fusible cast iron and melting this, for the first time removed the gangue of the ore; the third period by giving a temperature high enough to melt the most infusible forms of iron, liberated the slag formed in deriving them from cast iron.
Thomas, who showed that, in the presence of a slag rich in lime, the whole of the phosphorus could be removed readily.
Slag or Cinder, a characteristic component of wrought iron, which usually contains from 0.20 to 2.00% of it, is essentially a silicate of iron (ferrous silicate), and is present in wrought iron simply because this product is made by welding together pasty granules of iron in a molten bath of such slag, without ever melting the resultant mass or otherwise giving the envelopes of slag thus imprisoned a chance to escape completely.
Drops of Slag Props of Iron Layer of Molten Slag- -- --:€___ Layer of Molten Iron--- * The ore and lime actually exist here in powder.
7) the solid matter has become so hot that the now deoxidized iron melts, as does the slag as fast as it is formed by the union of its three constituents, the gangue, the lime resulting from the decomposition of the limestone and the ash of the fuel.
Hence from this level down the only solid matter is the coke, in lumps which are burning rapidly and hence shrinking, while between them the molten iron and slag trickle, somewhat as sketched in fig.
8), temporarily stopped with clay, at the very bottom, and the slag through another hole a little higher up, called the " cinder notch."
The fuel has, in addition to its duties of deoxidizing and carburizing the iron and yielding the heat needed for melting both the iron and slag, the further task of desulphurizing the iron, probably by the reaction FeS+CaO+C=Fe+CaS+CO.
The desulphurizing effect of this transfer of the sulphur from union with iron to union with calcium is due to the fact that, whereas iron sulphide dissolves readily in the molten metallic iron, calcium;sulphide, in the presence of a slag rich in lime, does not, but by preference enters the slag, which may thus absorb even as much as 3% of sulphur.
These foliaceous heaps lie along the bank like the slag of a furnace, showing that Nature is "in full blast" within.