Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/323

I E O N 307 some to different causes, such as compounds of vanadium and titanium. When, in addition to the "mine" or ordinary ores, the substances smelted contain an admixture of the slags from puddling and reheating furnaces, or of " mill cinder" (scales from the rolling mills used in the production of malleable iron), the blast furnace cinder is apt to contain an undue proportion of iron, these additional substances being usually much more compact in their texture than ores, and at the same time more fusible, so that their complete reduction is often not effected in the time during which they are traversing the furnace. Since these slags are usually highly con taminated with phosphorus and sulphur, they are only employed as a rule in conjunction with ores yielding the commoner qualities of iron, furnishing " cinder pig," which is often wholly white, and less carbonized and more impure than other kinds 01 white iron. The accompanying analyses illustrate the composition of the cinder produced in furnaces smelting various kinds of ore. 17. Utilization of Cinder. When the cinder does not contain too much lime or calcium sulphide, it often forms a material of moderate hardness and durability suitable for road metal ; but frequently it is of but little value for this purpose, owing to its friability and ten dency to fall to pieces on exposure to air and moisture. By casting the molten cinder (when of the requisite amount of durability) into rectangular blocks, a good substitute for building stone is produced ; in other cases, by the addition of alkaline silicates, a serviceable coarse bottle glass can be obtained. Vitreous cinders also serve for the preparation of a variety of "mineral wool," a filamentous sub stance something like spun glass producible by blowing air or steam through the molten cinder, and useful for packing the jackets of steam pipes, boilers, &c. , to avoid loss of heat, and superior for this purpose to organic substances in being not liable to char or burn. Certain kinds of cinder which approximate to cements in composi tion may be utilized in the manufacture of hydraulic mortars, Port land cement, &c. , by heating together with lime or hydraulic lime stone ; according to J. Huck, if the powdered slag be stirred up in a tank with dilute hydrochloric acid (containing some 17 per cent, of actual acid, HC1), sulphuretted hydrogen is evolved, and a partly gelatinized mass is produced by the decomposition of the silicates ; this when washed, drained, dried, and ground to fine powder, and mixed with finely powdered ordinary slag so as to constitute about 10 per cent, of the mixture, affords a cement capable of use for all sorts of work as well under water as above it, and equal in quality to the best cements in ordinary use. Bricks for building purposes may be made from suitable kinds of cinder by grinding it to a coarse powder, moistening and mixing with a little lime, and strongly compressing in moulds by machinery ; the brick sets in a few days to a hard stone-like mass ; some cinders will thus set without addition of lime by merely grinding up fine, moistening, and compressing. In order to facilitate the grinding, C. Wood has patented the following process : the molten slag as it runs from the furnace is received on a slowly revolving horizontal table and cooled by a jet of water (fig. 25), which causes it to disin tegrate into comparatively small fragments which are much more readily pulverized than the compact blocks formed when the molten slag runs into a receptacle and there solidifies ; or it is reduced to a kind of sand by running it into water kept in agitation by a pecu liar machine, the sand being a moderately useful manure for certain soils. See Journal I. and S. List., 1873, 186, and 1877, 443 ; and Journal Soc. Arts, May 14, 1880 (vol. xxviii. p. 576). At the Sclessin Works, Liege, slag sand is made without any machinery at all by simply making the stream of molten slag run into a con stant-running jet of water issuing obliquely from behind ; the slag thus disintegrates spontaneously into small fragments. Many FTG. 25. Wood s Slag Machine. kinds of cinder, however, are of so little value for any of these pur poses that they constitute a wholly waste product, the getting rid of which in the cheapest way possible is a desideratum. 18. Collection of Waste Gases. To M. Aubertot of the department of Cher belongs the credit of having first attempted to utilize the gases escaping from blast furnaces, in 1811 ; a brick kiln being erected on the top of the furnace, the flame was allowed to pass in and so burn the bricks ; the calcination of lime and the heating of the chests containing charcoal and iron bars for steel cementa tion was effected by him in the same way. In later years steam boilers were heated in much the same way ; about 1840, at the Rustrel furnaces (department of Vaucluse), the device was in use of drawing off the gases by means of a tube and burning them underneath the boilers placed, not on the top of the furnace, but in any convenient place even though at some distance. The use of the waste gases for heating the blast on this principle was patented in Eng land by J. Palmer Budd in 1845. A few years later George Parry of Ebbw Vale adapted an old arrangement for distributing equally the charges introduced into the furnace (by shooting the materials on to a conical surface at the mouth of the shaft) so as to form a kind of valve, closing the furnace entirely when shut and allowing the gases to pass out completely into a tube conveying them to the places where they were to be burnt, and at the same time allowing the charge to be introduced almost instantane ously when opened. This "cup * and cone " arrangement is re presented in fig. 26. By simply lowering the cone (counterbalanced) the materials shoot off it into the furnace ; by immediately raising it the furnace is again closed ; on account of its simplicity and ease in working it has been very largely adopted, especially as it facilitates the proper distribution of materials inside the furnace by making them glide off the slanting conical surface so as to be deposited at the sides of the shaft and not at its centre ; the effect of this is to tend to make the upper surface of the mass concave instead of convex, and in consequence the lighter coke or charcoal tends to roll down the slope towards the centre somewhat more than the heavier ore and flux, so that the central portion of the mass of materials in the shaft is somewhat richer in fuel than the sides ; if the furnace is full nearly to the throat and of considerable width, the surface will be crater-shaped, the heavier ore, &c., accumulating in the circular crater ridge, and the lighter coke rolling down inwards towards the centre, and outwards towards the side of the shaft. As the materials sink the outermost layers are retarded by friction against the sides