The amount of work got out of a ball furnace varies with all different circumstances and mixtures, but as a rule, a workman can draw nine balls in an eight hours' shift, well worked and fired, and weighing about 4 cwt. 3 qrs. each.
The exact nature of the changes wrought in the ball furnace is still but imperfectly understood. For a full description of all the chemical theories which have been from time to time advanced, the reader is referred to the many papers that have been published upon the subject. The simplest view is, that first the sulphate of sodium is reduced to sulphide by the action of the coal, and that then a mutual decomposition takes place between this substance and the calcium carbonate, sodium carbonate, carbon dioxide, and a mixture of calcium sulphide and oxide being produced. The analysis of black ash is not only very intricate, on account of the number of constituents, but is also exceedingly uncertain, from the variety of the materials used and the circumstances attending sampling and testing operations. Tho following, however, may be taken to represent the composi tion of a good and well-worked ball :— In the year 1853, the first "revolving," or mechanical, ball furnace was patented by Elliott and Russell. This apparatus is designed to do away altogether with the necessity for hand labour in the balling operation. Many difficulties have had to be overcome, but at length, thanks to the improvements of Messrs. Stevenson and Williamson, and James Mactear, and to more perfect mechanical contrivances, the " revolvers " bid fair, in large works at least, to supersede the old hand furnaces. The annexed drawings, Figs. 246, 247, and 248, show the complete apparatus as designed and constructed by Messrs. Robert Daglish and Co., of St. Helens. Heat is supplied by Siemens' patent gas arrangement in the plan set forth. The more usual custom is to employ the ordinary coal fire. Gas is being daily more and more applied to various purposes in the alkali manufacture, but its introduction is comparatively slow, owing to an expensive plant being required and the influences of deeply rooted prejudices. The saving of fuel effected is not very considerable, but for all purposes where an exact regulation of heat is an important point, the superiority of gas cannot be denied. Fig. 246 gives the side elevation of the revolver and boiling-down pan ; Fig. 248, the end elevation ; and Fig. 247, a plan of the whole. A A is the gas flue from the generator ; B B the
inlet for regulating the supply ; C C the combustion chamber ; D D inlet for heated air ; E E a ring to allow of the contraction and expansion of the cylinder ; F F the revolving cylinder itself, built of boiler plate, half an inch in thickness, lined with firebricks and blocks. The shell is about 15 ft. in length and 10 ft. in diameter, put together in the most careful and substantial manner possible, strengthened by two strong cast-iron rings riveted firmly to it, and hooped with solid east steektyrcs shrunk hot upon the rings and securely bolted: G is the charging door when at the top and the discharging door when the position of the cylinder is reversed. H H are the friotion rings working upon the steel-tyred friction rollers I I. J J are the bearers resting upon strong iron plates, K K. L L are waggons for receiving the ball when discharged, running upon a small tramway. M M a high pressure upright ongine for driving the cylinder and working the tramway, the speed being capable of the most delicate regulation by suitable gearing. N N is a flue for supplying heated air to the combustion chamber. This air is introduced through the upright east-iron beater 0 0, and warmed by the waste heat from the furnace. P P is the boiling-down pan; R R the drainer, and Q Q a tank for settling the black ash liquors and supplying them to the pan. This tank forrru3 of course no integral part of the arrangement ; its position is merely a matter of convenience and economy. When direct firing is adopted, the neck of the cylinder is formed with a loose iron rim lined with firebricks. Through the space on either side of this rim a constant indraught of air takes place, which materially assists in the complete combustion of the gases. It is also possible to ascertain through this opening the state of the charge within the cylinder. In place, too, of the heater 0 0 is built a dust chamber between the furnace and boiling-down pan, to collect the waste from the fire, and prevent the sulphate, itc., from the charge, being drawn over into the black salt. It will be noticed, by referring to Fig. 246, that the interior of the cylinder is barrel-shaped, to assist in the concentratiOn of the charge. This form is given by the brickwork lining. The entire cost of a first-class revolver, with pan, engine and over-head tramway complete, is about 2000/.