The quantities of coal used in the manufacture of salt vary according to the kiads of salt, and also somewhat in the different works. The boiled salts take the most coal, as the gases leave the pans at high temperatures. Common salt is about the most economical of fuel, the different fishery-salts and bay-salt occupying positions intermediate in this respect between the two. Fine salt takes about 13 cwt. per.ton of salt ; part of this heating power goes to maintaia the temperature of the stoving room. Common salt should take but 9 cwt. of coal per ton of Salt. The fuel used in the Cheshire salt-works is the small coal called " slack" from Lancashire and Staffordshire ; and " burgey," e. small and large mixed just as they come from the mine, mixed with the slack or by itself, is often used for boiled salts. Small coal is preferable for produoing the mild heat required in salt-making, and has tho further advantage of cheapness.
The innovations introduced of late years in the salt manufacture require to be shortly alluded to. Both in England and abroad, attempts have been made to reduce the less of heat, chiefly due to the scale in the pans and the soot of the flues, by heating by steam. Whatever economy there may he in this method, it has not made much progress among English salt-makers, though the system is a common one for other purposes in the salt districts. The steam-pipes get covered with scale, which is difficult to detach without injury to them, and they are rather in the way of drawing the pans.
So-called "machine-pans " are employed at the works of Verdin, Falk, and the British Salt Co., and probably elsewhere. These are round pans, Figs. 1212-4. They are usually worked in pairs, standing 20-30 ft. apart, with a small engine f between, or a shafting d running above several of them driven by an engine at one end ; this shafting is geared by bevel-wheels e to the stirrers a, and is so arranged that any one or more of the pans can be thrown into Or out of gear at will. The depth of the pans is 2 ft., and an opening is left in one side of each down to the bottom, this opening being closed with outside troughs b riveted to the sides of the pans. The bottoms of these troughs go lower than the bottoms of the pans, so that any salt swept out of the openings falls into the troughs, and cannot return into the paus. The pans are fitted with conical covers of sheet-iron, through the centre of which pass iron spindles, geared above to the pinions of the shaft ing hy bevel-wheels, and resting on the bottoms of the pans, in which they are free to turn. These spindles are attached at their lower parts to the arms or stirrers a carrying scrapers swinging loosely beneath them, and resting on the bottoms of the pans. The covers are fitted steam-tight upon the tops of the pans, and each is provided with one or more manholes /, by which workmen cau enter to clean the pans. Those parts of each cover corresponding to the parts left open in the sides of the pans are brought down so as to partially close the openings and come just low enough to dip into the brine about 2 in., when the pans are about 2 filled, while the spindles passing through the covers turn in stuffing-boxes. Thus, when the pans are closed, they are steam-tight, and there is no exit for the steam unless by forcing the water out of the pans into the troughs b, or passing off by the flue,s h. Each pan is fired by 3 fires, and boiled as for fine salt, while the spindle carrying the arms and scrapers is made to rotate. The incrustation of the pans is thus for the most part avoided, while very fine salt is produced, and is swept by centrifugal motion into the troughs, whence it is continuously laclled with a scoop, drained on " hurdles "c, and sent to the stove or the butter-salt bins, as the case may require. The steam-pipes discharge beneath the two fishery-salt pans, occupying the central position in the figures, while the gases from the fires under the pans, and perhaps from the fire of the engine, are made to pass to the flues beneath the outer pans. Both the pans which are heated by the steam stand on short brick or iron columns without flues ; the pans taking the waste gases are set upon winding flues such as already described as being in frequent use in France.
At the works of the British Salt Co., at Anderton, a 3-4-H.P. engine stirs three pans, and it is stated that, with a consumption of 40 tons of coal, a pair of these pans, with their concomitant fishery-salt pans, will turn out 60 tons of fine salt and 24 tons of fishery-salt per week. The fine
salt produced in these machine-pans is very fine and fairly white, but usually contains just a trace of iron, which communicates to it the faintest possible shade of yellow.
Sometimes au ordinary boiling-pan is mounted with a fishery-salt pan behind it, so that the flues from the former passing beneath the latter, this pan also becomes heated by the waste gases. The Cheshire Amalgamated Salt Co., one of the largest and most important of the district, have in their works at Winsford some rather interesting and peculiar composite pans, known as " clay " or " tank " pans, also working on this principle. Fig. 1215 represents a ground plan of this arrangement, and Figs. 1216, 1217, 1218, are transverse sections on the lines D E, F G, B C, respectively. The boiling-pan a is placed with its upper edge on a level with the ground or barely above it. It is of the usual depth of 1 ft. 9 in., and of the form shown. The fishery salt pan b utilizes the waste beat of the furnace-gases, after they leave the flues beneath a. There are 3 fire-places f, and 3 flues e, beneath a, together with 2 dead flues. Alongside of and pat allel with the pans a b, is u pit or trench 0, about 4 ft. deep, 10-12 ft. wide, and 38-40 ft. long. It is puddled with clay and lined with bricks throughout the sides and bottom. The upper edges of this trench are about 4-5 in. below the level of the upper edge of the pan a. A parting wall of brickwork also divides this trench c longitudinally into 2 compartments of equal width. This wall, however, only goes to within about 10 ft. of the end of the trench furthest from the fires, and to within 2 ft. of that end which is iu a line with them. The side of the pan a turned towards the trench is cut out at the cnd furthest from the fires, and a shallow channel of sheet-iron, just as deep as the pan, connects it with the double trench, while the space k contained between a and the trench is filled up with a bed of masonry, the surface of which slopes gently from the upper edge of a towards c, so that the waste brine from any salt drawn on to it may drain into c. k is connected with d, as shown in Figs. 1215 and 1217, by a short wall, and a pump is placed at h, while another sheet-iron channel, only 2 ft. wide, but of the same depth as leads between the pump and the pan a. There is a small pit g, made of masonry, at the end of this channel ; and at tbe eud of the parting wall, at d, is a flat space just large enough for a man to stand upon to look after the pump when requisite. With this arrangement, if brine be poured in by the brine pipe i, c will be filled, and if the influx of the brine be con tinued, a and b may be filled till c is nearly overflowing, and a becomes full to within 4-5 in. of its upper edge. If then the pump h be worked so as to lift the brine from c and cause it to fall into g, it will flow back into a, and, circulating through a, will pass again into c; thus a steady circulation of the brine may be maintained in the directions shown by the arrows on the ground plan, so leng as the pump is kept going. If then the fires f, Fig. 1218, bo lit, the brine will be heated in a, and, circulating in the manner de scribed, expose a large evapo rating surface. The heat is so managed in these pans as to produce butter-salt in a and common salt in c; while at g, whet.° the pump produces con stant agitation, very fine salt is formed. Around the clay pan, the butter-salt pan, and the fish ery-salt pan, are the usual paths for the circulation of the work men, and thc places for the so called " hurdles " al upon which the salt is thrown to drain. The ; stoke-hole is below the level of the ground. The fishery-salt pan b may be, mounted on columas of brickwork or east iron without separate flues, and a chimney at the end of this pan carries off the furnace-gases. These pans seem to produce very fine qualities of salt, par ticularly the common salt from the pit c. The yield is about the same (as regards weight of mit to weight of coal consumed) as with the ordinary pans, but the repairs are somewhat less, and certainly the qualities of salt produced are very fine. The chief drawback to them is a rather greater tendency of the pan a to become coated with scale, than in the case of the ordinary butter-salt pans.