Waste Products, UTILISATION OF. By 'waste' is generally meant such material as is rendered either wholly or partially useless in the manufacture of products and articles of all kinds, but the name is sometimes retained long after a substance, at one time of little or no value, has been utilised. 'Waste-silk,' for instance, is now a valuable material, although this name for it is kept up. If envelopes are cut out of a roll of paper, parts of dress out of a web of cloth, and round covers out of sheets of tinplate, 'waste' pieces are unavoidably left. There would be more loss than gain in manufacturing such materials into the shapes required for specific articles. Again, when iron ore is smelted, or coal distilled, or common salt converted into soda, waste in some form results from the operations. In every manufacturing process, mechanical or chemical, there is waste. The examples given relate to new waste, but nearly everything we use wears, or corrodes, or gets broken or unshapely, and so rags, and rust, and scraps arise. Rags of all kinds are nowadays so much in demand that they are only waste in a nominal sense. On the other hand, the rust which arises from corroding iron is utter waste, since it can never be profitably collected at all. In respect to the value of 'waste,' these two, among familiar things, may be taken as at opposite extremes.
There is a kind of waste, for the most part difficult to prevent, which goes on in the consumption of fuel, and in certain processes of roasting or calcination in the smelting of metals. Roundly speaking, the best designed steam-engines and boilers require only half as much coal per horse-power per hour as those less skilfully constructed, and the fuel unnecessarily consumed by bad boiler-furnaces is largely wasted as smoke through imperfect combustion. The Siemens regenerative furnace (see Vol. V. p. 239) is most ingeniously constructed for the saving of waste heat. The utilisation of blast-furnace gases (see IRON) for heating purposes, and the recent recovery of Tar (q.v.) and ammonia also produced by the coal consumed in these furnaces, form an instance of a double saving from the same source. In the report of the chief-inspector of alkali works for 1891, it is stated that the plant put up in recent years for collecting tar, ammonia, &c. at fifty-seven Scotch blast-furnaces has cost £444,600, a sum fully equal to the cost of building the furnaces themselves. The condensing flues, miles in length, connected with some lead-smelting furnaces (see LEAD) are modern examples of appliances to condense lead fume or smoke which formerly was allowed to escape, causing much loss of lead. In striking contrast to these we may state, while speaking of gaseous products, that over a large district in the south of Spain where cupreous iron pyrites occurs abundantly the barbarous practice is being continued of burning this pyrites in the open air (to get rid of its sulphur and so lighten its weight), to the destruction of vineyards and other vegetation, and to the loss of an enormous amount of sulphur sent into the air in the form of sulphurous acid. The acid used in 'pickling' iron plates which are to be tinned or galvanised is now recovered. See GALVANISED IRON, and TINPLATE; also NAILS, for use of tinplate scraps.
Some instances of how waste in a solid form arises in working rock and other mineral substances may now be given. In shaping and dressing granite paving-stones as much as three-fourths of the rock quarried is, in some instances at least, wasted. This waste is as yet only very partially utilised for road-metal, and in small chips for 'granolithic' pavements. Coal 'dust' is made into Briquettes (q.v.) for burning in fires. The utilising of the vast waste heaps of spent shale at the Scotch mineral-oil works is a problem which awaits solution. The oil shale of the carboniferous formation in Scotland, from which Paraffin (q.v.) and paraffin-oil are obtained, was itself looked upon as of no value till 1859. Blast-furnace slag (see SLAGS) is now utilised in several ways, and in a number of cases the accumulations of other kinds of slag on the sites of ancient smelting-works have, in modern times, been again put through the furnace to extract the metals left in them, with profitable results. Some of the refuse from the old silver-mines of Laurium (q.v.) has been bought up by capitalists for this purpose. One instance, though not of very recent date, may be given where, by the production of a by-product, a fortune was very quickly amassed. About 1840 Mr Askin of Birmingham discovered a method of separating cobalt, in the form of oxide, from nickel, two metals which were very difficult to separate. This oxide of cobalt was at first a waste product, but before very long it was put into the hands of potters, who readily bought it up to produce a blue colour on their ware, at the then rate of two guineas per pound. Among comparatively recent instances of utilisation of by-products and waste products in the chemical industries, we may refer to the importance of the substances now extracted from Coal-tar (q.v.), and the great value of some of them in the manufacture of dyes (see DYEING). Another example is the recovery of bin-oxide of manganese in the production of chlorine for the manufacture of bleaching-powder by Weldon's beautiful process. Formerly for every 100 lb. of bleaching-powder made about 100 lb. of the native oxide of manganese were required. Now this manganese is recovered and used again and again in the process, with only a loss of about 5 per cent. to make up each time it is returned to the chlorine still. The earlier methods of recovering manganese were not nearly so perfect, and therefore were not much used. A process for the utilisation of chemical waste on a great scale is Chance's method, patented in 1888, of recovering sulphur from alkali makers' black-ash refuse (see SODA).
Passing to vegetable substances, the various materials besides Rags (q.v.) used in the manufacture of paper may be first noticed. Straw, wood, and esparto fibre, if not exactly waste pro- ducts, were at least undeveloped substances before they became, as they now are, so largely used in paper-making. Old ropes, flax and jute mill waste, old or torn pieces of paper of every kind, are all serviceable in paper-mills or in the manufacture of Millboard (q.v.). In the pulp of the latter old newspapers bulk largely. Cotton waste is much used by mechanical engineers for cleaning purposes. Sawdust (q.v.) is employed in several ways. Cork-cutter's waste has become of high importance in the manufacture of linoleum and cork-carpet (see FLOORCLOTH). From the bark stripped from osier wands the useful medicine salicin is now made. In days not so long past the spent madder of our large dyeworks was suddenly raised from a useless to a valuable material by treatment with sulphuric acid, which converted it into the dye called garancin. Madder itself, which till 1869 held a chief place among our dyestuffs, has since become of trifling importance, through the introduction of artificial Alizarin (q.v.). This is hardly the place to refer to the utilisation of Peat (q.v.), but it may be remarked that this material, so abundant in Ireland and Scotland, is in Russia, Germany, and Holland turned to profitable account in several ways, by methods which have not yet succeeded in Britain. From the seaweed thrown up on our shores iodine is obtained, but, although some is also used as manure, much of it is allowed to decay (see KELP). It is to be hoped, therefore, that the Algin (q.v.) which has been prepared from it will become a marketable product.
One of the most interesting examples of what has been done in converting a waste animal product into a highly useful material is seen in the case of waste-silk. Cocoons do not yield half their weight of reeled silk, but the remaining 'waste' portion has, through the ingenuity of an English inventor, become the raw material for a large spun-silk industry (see SILK). In Venice artificial flowers for ladies' head-dresses are made of imperfect cocoons. The various kinds of waste from woollen mills and from the cutting up of woollen fabrics are either worked up again into yarn or felt, or are ground into flock for paper-hangings (see SHODDY, and WALL-PAPER). Glue (q.v.) is made from parings of hide and from bone. The turnings and dust of the ivory and bone turner have various useful applications. Prussiate of potash (see FERRO-CYANOGEN) is made from almost any waste animal matter, such as parings of horns and hoofs, hair, blood, leather-cuttings, and even field-mice.