On the Continent, other dispositions of flues are often adopted. At Nancy, and pretty well thronghout Franee, the flues from each flre (often only two) run down to the end of the pan, returning towards the flre-end, and back again once more to the chimney or main flue, each flue thus forming 3 parallel lines. This plan has been trie,d in England, but is not now usually em ployed, the simpler form of straight flues leading from each flre right away to the chimney or common flue seeming generally to be preferred. Here in England also they usually have two " dead " flues, as they call them, one on each side beneath the pan, these being spaces like flues, but completely walled up at each end, so that no gases can enter them, as shown in Fig. 1225, p. 1739. This represents the arrangement of flues now generally adopted. The flues are usually 2-3 ft. deep, of a capacity in fact to admit a man or boy ; and between the entrance of the flues and the flre-plaeu, is built a wall of flre-brick, reaching to within 18 in. of the bottom of the pan. Over this " bridge," as it is called, the heated gases pass before entering the flue, and ss the bricks of the bridge become red-hot, they tend to induce a more perfect combustion of the smoke before it enters the flues, where it would become too rapidly cooled by contact with the bottom of the pan, and soot would fall.
In Cheshire, and other places in England, the evaporating-pans are at times employed quite open and exposed to the sky, but nowadays they are mostly surrounded with sheds, these being furnished with ventilating openings in the roof, to facilitate the escape of steam. On the Continent, all except the flne and butler-salt pans are generally covered in with wooden trunks, flat on top with sides converging upwards, thus forming an elongated truncated cone about 5 ft. high over tho pan. All along the lower parts of the sloping sides of this cover, and on both flanks of it, are frames fitted with shutters retnovable by hand. By removing one or other of these, the progress of the crystallization may be watched. A shelf is sometimes made, running along the whole length of this cover of the ps,n, just above the shutters ; and when the pan Is drawn, the workmen fish out the salt with rakes and scoops, and let it drain a bit on the drainers along side of the pan, corresponding to what our salt-makers call " hurdles," and then pitah it overhead on to this shelf, on which it is allowed to drain pretty completely, the drippings falling back into the pan ; thence it is shovelled on to the flat top of the cover of the pan, which is set with tiles. On these tiles, which are kept hot by the steam within the trunk during the time the pan is at work, the salt 'becomes dried, and is then on a level with the bins (magasins) into which it is tipped from waggons for storage. From that end of the trunk furthest removed from the fires,
rises a wooden chimney 10-15 ft. high, for carrying off the steam frotn each pan ; it passes through the roof of the building in which the work is carried on. Sometimes fan-blowers are placed in this and the i9oain chimney, to expedite the exit of the steam. It is asserted by many of the Frenoh salt-makers that notwithstanding the greater cost of covering in the pans in this manner, the lessened facility of egress for the steam, the inconvenience, and the somewhat larger amount of labour involved in drawing the pans, they are compensated by a considerable economy in the combustible employed, through the diminished loss of heat by radiation ; certainly they obtain cleaner products than English salt-makers. At the Dombasle salt-works, one of the best-managed and best-organized in France, the writer has, on the contrary, noted that with 100 kilo. of the small, poor coal from Saarbriick they only produce 160-170 kilo. of common salt. This coal is, however, far inferior to the slack used in Cheshire and Worcestershire, and it is not employed for flue or butter-salt, lacing unable to maintain a pan in continued ebullition, so small is its heating power. It is used on account of its low price, and its yielding a gentle diffused heat suitable for the work.
Tim stoves in which " lutnps " of flne salt are dried in England are low rooms usually placed at the ends of the butter and flue salt-pans. Through these pass the flues conveying the still heated gases to the ellimney. The gases from the boiling pan,s are employed by preference, as they emerge at a higher temperature than from the non-boiling pans, and the flues conveying them become very strongly heated, Sometimes these flues are carried below the ground, sometimes above, the intervals between them being then termed " ditches." In either case, the flues are covered with east-iron plates, and are made to wind about in the stove-room, so as to present a considerable radiating, surface. The temperature of these rooms is usually 49°-65i° (120-150° F.), often even higher. The floor of the room and the iron plates covering the flues are bestrewn with common white or ground rock-salt, to an inch or two in depth, and this forms a warm, dry, and absorbent bed of material on which the lumps of salt rapidly become dried. Their dryness is recognizable by their peculiar ring on being struck, as cotnpared with the duller sound they en9it while at all moist.