SCIENTIFIC NEAVS. 



[Nov. 1st, 1887- 



THE UTILISATION OF REFUSE. 



THE theoretical condition in every manufacturing pro- 

 cess is, that every article taken in hand should issue 

 from the works in a useful, and therefore, saleable state. 

 In most cases, however, there is a fairly wide margin between 

 this ideal state of things, and that which hitherto has been 

 reached in actual practice. This margin is waste or refuse, 

 and means diminished profit to the manufacturer, indirect 

 loss to the cominunity, and sometimes, in addition, a nuisance 

 actual or potential. Hence there exists among inventors 

 a very natural and laudable desire to reduce this source of 

 loss, either by preventing the refuse from ever being formed, 

 or, if formed, by turning it to some account. In many 

 instances these attempts have been successful, and it may 

 be said that millions have been thus gained by the utilisa- 

 tion of matter heretofore a mere encumbrance. Entire 

 new branches of industry have thus sprung up. But there 

 is one grave difficulty always in the way; any manufacture 

 which takes as its raw material the refuse of some other 

 manufacture may find itself suddenly stranded, if, in conse- 

 quence of some improvement, it is turned out only in very 

 restricted quantities. 



Thus at present hydrochloric acid is, if not a refuse, yet 

 a bye-product of the alkali manufacture on the Leblanc sys- 

 tem. On a plentiful and consequently cheap supply of this 

 acid depends the production of chloride of lime, the main- 

 stay of the bleacher's business. But it seems not unlikely 

 that the Leblanc process will be superseded by the Solvay 

 process, in which hydrochloric acid, if produced at all, will 

 not be turned out incidentally as a waste product seeking 

 application. In that case it would have to be made specially, 

 and its price would necessarily rise. The cost of chloride of 

 lime would then rise, and the bleaching both of linen, cotton, 

 and paper, would become more expensive. 



As an instance of a waste product which has entirely dis- 

 appeared, may be mentioned the solution of chloride of 

 manganese from the chlorine stills. This liquid was at one 

 time to be had for fetching away, and was useful, amongst 

 other purposes, for the treatment of sewage, and for disin- 

 fection generally. But since the great improvement in the 

 manufacture of chlorine, for which the world is indebted to 

 the late Mr. Weldon, this refuse is no longer produced. 

 The manganese from the stills is regenerated, and can be 

 used over and over again. Hence, those who want chloride 

 of manganese for any purpose can no longer obtain it as a 

 waste product, but must make it especially at a higher cost. 



The iron manufacture throws off an enormous quantity of 

 refuse in the form of slag. To such an extent is this waste 

 produced, that some iron-masters have even been under the 

 necessity of renting large plots of land to receive it. Of 

 course, many attempts have been made for its utilisation, and 

 not without success ; but none of them consumes anything 

 like the quantity which, in one way or other, has to be 

 got rid of. In some parts of England and Scotland, it is 

 used as a material for making and mending roads. The 

 huge blocks of slag, still very hot, are conveyed away in 

 iron-carts, and laid by the roadside until sufficiently cool to 

 be further dealt with. In the neighbourhood of Brighouse, 

 Bradford, etc., it is common to see boys roasting potatoes 

 by laying them on the hot masses. 



It has been proposed to cast the slag into blocks about 

 the size of bricks, and to use them as a building material. 

 But as far as dwelling-houses, work-rooms, etc., are con- 

 cerned this project was found impracticable, owing to a 

 difficulty mentioned in the article on ventilation in our June 

 number. Slag-bricks may serve for the inclosing- walls of 

 court-yards, etc., but this does not create by any means a 

 sufficient demand. 



Another and more successful attempt has been made by 

 Mr. Bashley Britten at Finedon, in Northamptonshire. He 

 takes the molten slag as it runs from the furnaces, and con- 

 verts it into glass by the addition of a suitable proportion of 

 silica (sand) and alkali. It is essential for this process that 

 the glass works should be very close to the blast furnaces. 

 In this manner not only is the cost of carriage, loading and 

 unloading saved, but the heat of the slag is utilised, and thus 

 a great economy of fuel is obtained. If the slag were first 

 allowed to solidify before being run into the tank of the 

 Siemens' furnace and mixed with the other ingredients, its 

 use would scarcely be remunerative. 



Some quantity of slag is consumed in the manufacture of 

 the so-called slag- wool. Whilst in a molten state it is 

 brought in contact in a thin stream with a current of super- 

 heated steam, and is by this means converted into a mass 

 of filaments or fibres, somewhat resembling coarse wool in 

 appearance. The value of this material lies in its being a 

 very poor conductor of heat. Hence slag-wool may serve 

 as a covering for steam-boilers, steam-pipes, and pipes 

 conveying hot liquids which have to be protected from cool- 

 ing. This use would secure for slag-wool a very consider- 

 able demand if there were no rival in the field. But 

 asbestos or amianthus, a natural mineral which occurs in 

 fine fibres, almost silky masses, answers all the purposes to 

 which slag-wool can be put at least as well, and as it is 

 found in abundance in many parts of the world, the future 

 of slag-wool appears doubtful. 



It has also been proposed to utilise ordinary blast-furnace 

 slags in the manufacture of alum, alum cake, and other pre- 

 parations of alumina. For this purpose the slag, as it 

 issues from the furnace, is allowed to fall into a tank of cold 

 water. It is thus resolved into a powder, and is then easily 

 acted upon by acids. For preparing cheap, crude sulphate 

 or chloride of alumina for sanitary purposes, the treat- 

 ment of sewage, etc., this process answers admirably. But 

 for the manufacture of fine alum for the use of the dyer and 

 calico-printer, it is not yet proved that this method presents 

 any advantage over the ordinary processes, where bauxite, 

 cryolite, or china-clay serves as the raw material. 



So far, then, the projects for the utilisation of iron-slags 

 fall far short of keeping up with the supply of a refuse 

 which is accumulating at the rate of 8,000 tons yearly. But 

 a change is occurring wherever the so-called " basic pro- 

 cess " of Thomas and Gilchrist is found applicable to the 

 ores smelted. The slag produced in this case is quite 

 different in its composition from the slags of the old process, 

 and is applicable to quite different uses. It contains from 

 fourteen to twenty per cent, of phosphoric acid, according to 

 the different qualities of ore worked upon. Hence if ground 

 to powder it has a great agricultural value, and is already 

 used by farmers to an enormous extent. This sale and use 

 naturally interferes with the superphosphate trade. A;peT- 

 centage of phosphoric acid in the Thomas slag, being a refuse 

 product, can, of course, be offered at a lower figure than a 

 percentage of the same acid in the form of superphosphate, 

 bone-manure, etc., which has to be specially manufactured. 

 Hence a serious blow has been given to the chemical manure- 

 maker, and to all persons employed in mining for apatite, 

 phosphorite, coprolites, or any other phosphatic minerals. 

 This is an instructive example how an improvement in some 

 branchof industry may derange and even paralyse someother 

 branch, with which it does not seem at all to come in 

 contact. 



But some Thomas slags contain another material which 

 has lately become of technical importance. This is vana- 

 dium, a metal which until lately was known only as a 

 chemical curiosity, and which in a pure state was valued 

 at upwards of is. per grain ! It proves, however, to be 



