118 ALUM 



weeks which formerly would have occupied many months. For certain purposes, 

 however, the old-fashioned Whitby alum is still preferred. 



IIL Alum Manufacture from Coal-Measure Shales. The manufacture of alum has 

 of late years taken an entirely new shape, and tho two processes of Mr. Sponco and 

 Mr. Pochin have absorbed tho whole of the manufacture in the north-west. 



Mr. Spence, who has a manufactory of ammonia-alum at Newton Heath, near 

 Manchester, called the Pendleton Alum Works, has now become the largest maker of 

 this substance in the world, as his regular production amounts to upwards of 150 

 tons per week. His method of manufacture is also largely carried on at Goole, in 

 Yorkshire. In Spence's process, which he patented fifteen years ago, he uses for the 

 production of his sulphate-of -alumina solution tho carbonaceous shale of the coal- 

 measures. 1 This substance contains from 5 to 10 per cent, of carbonaceous matter, 

 and, when ignited by a small quantity of burning coal, the combustion continues of 

 itself. The raw shale is piled in heaps about 20 feet long, 4 or 5 feet high, and 2 or 

 3 feet broad. To supply air during tie calcination of tho shale, a brick drain is con- 

 structed under each heap. The calcination occupies about ten days, and must be 

 conducted below a red heat ; at higher temperatures, the material has a tendency to 

 vitrify, and the alumina thus becomes insoluble in sulphuric acid. After calcination, 

 the shale is removed to the pans, in which it is treated with oil of vitriol. These 

 pans are each about 40 feet long, 10 feet wide, and 3 feet deep. They are constructed 

 of sheets of cast iron, screwed together, and lined with lead, and the bottom of each 

 pan before use is covered with earthen tiles about 9 inches square. A charge of 20 

 tons of calcined shale is introduced into each pan, and digested with about 10 tons of 

 oil of vitriol, of specific gravity 1'25, which dissolves out the alumina of the shale. 

 The digestion is conducted at a temperature of 220 F., this temperature being main- 

 tained partly by fires under the pans, and partly by the introduction of hot gaseous 

 ammonia evolved from the gas-liquor evaporated in boilers. A double sulphate of' 

 alumina and ammonia, or ammonia-alum, is thus formed. After being heated for 

 four or five days, the liquor is drawn off into the coolers, which are large shallow rec- 

 tangular vessels of lead, each about 29 feet long, 17 feet wide, and 1| feet deep. In 

 these vessels the liquid is kept in constant agitation by means of a long wooden arm, 

 worked by steam. The formation of large crystals is thus prevented ; but, after tho 

 lapse of about fourteen hours, the small crystals, which then form a bed several inches 

 thick at the bottom of the vessel, are removed, and thrown into a large square box, 

 lined with lead, in which they are washed with tho mother-liquor, and having drained 

 are thrown upon an iron grating formed of bars set about half-an-inch apart. The 

 masses of crystals are thus broken, and the mother-liquor washed out. The crystals 

 are then transferred to a cylindrical vessel, two or three feet high, and about 2 feet 

 in diameter. This vessel has two divisions, one open and the other closed. The 

 alum is placed in the open compartment, and dissolved by means of steam, introduced 

 at a pressure of about 20 Ibs. per square inch, through holes in a coil of leaden pipe 

 at the bottom of this division of the vessel. A pipe leads from the top of the cylinder 

 .to a wooden vessel, called tho dissolving box, which receives the solution of alum 

 before it is drawn off into the roching pans. This box is 3 feet deep, 14 feet long, 

 and 8 feet broad ; it is covered with boards, the joints between which are closely 

 packed with cotton waste. After tho solution has remained for some hours in this 

 vessel, a quantity of size about 4 quarts is poured in, and the suspended impurities 

 are thus caused to settle. The clear solution is tapped off from the dissolving box 

 into the crystallising tubs ; each tub is about 6 feet high, and wider below than above. 

 At the bottom of each tub is a round flagstone, upon which the staves of the tub, 

 lined with lead, are built up and kept in place by strong iron hoops screwed together. 

 The hot solution is run into these tubs, and protected by a wooden cover. After 

 standing for about forty days, a sufficient thickness of alum will have crystallised to 

 allow the sides of the tub to be taken down. The block is allowed to stand for about 

 a fortnight longer, and a hole is then made in the lower part of the block, through 

 which the mother-liquor runs out, and is received in tanks. On breaking open the 

 block, the sides of the internal cavity are found to bo studded with fine octahedral 

 crystals, presenting a slightly violet tinge. These blocks weigh about 4 tons each. 



IV. Alum Manufacture from Mineral Phosphates. In 1870 Mr. Peter Spence 

 patented a novel process for manufacturing alum, using as his raw material a phos- 

 phate of alumina and iron obtained from the Island of Kedonda, near Antigua, in the 

 West Indies ; other mineral phosphates containing alumina may, however, be 

 employed. 2 The v process has special value, since not only is the alumina of the 



1 This description of Spence's process is taken from a paper on ' The Past and Present History 

 of Alum,' by J. Carter Bell, Esq. F.C.S., Associate of the Koyal School of Mines. ' Chemical News/ 

 vol. Jdi. 186fi, pp. 221, 234. 



Specification of Patents, A.D. 1870, No. 1676. 



