It will be seen that by this process the whole of the chlorine is made available, and is actually utilized, so rendering possible an immense production of bleaching powder. A small loss of material is incurred from mechanical sources—leakage, &c.—but this may be reduend to 2 or 3 per cent. by a carefully constructed plant. The apparatus required is of simple description, and is in no way liable to get out of order. And yet, probably on account of the unremitting care required in conducting all the various operations, and the possible amount of mischief resulting frorn neglect or carelessness, the process has never been practically auccessful. It will be readily appreciated from the foregoing details that there are many points which are likely to prove veritable rocks of offence. If the proper proportions are not kept between the manganite and acid in the still, so much magnesia has to be added to the liquor, that the furnace product contains an undue amount of this substance, which is of course worse than uselesa in the still. Again, if the amount of protoxide in the man ganite—answering to the " base" of the Weldon manganese recovery process—is large, a, waste of acid results in the still operation. The regulation of the temperature of the furnace, and the admission of air, are likewise delicate matters requiring constant attention. The process has been worked by several manufacturers upon a fairly large scale, but is now entirely abandoned in favour of the more successful lime recovery process. • Other plans for the regeneration of manganese have been proposed by Hofmann, Kuhlmann, Schloessing, Elliott, and others, but have never got into the region of practical manufacturing upon a large scale.
Of the various processes for the production of chlorine without the Me of manganese, that of the late Mr. Deacon deserves prominent notice. Beautifully simple in reaction, productive of an enormous yield of\ cheap chlorine, this process is not at all unlikely, in some revived and modified form, to aupersede all others. At the present time it is practically abandoned on account of certain mechanical difficulties which militate against its continuous and effective operation.
Deacon's process miginated probably in two already patented but unsuccessful methods of obtaining chlorine. The one waa that of Laurens, and consisted in heating dry chloride of copper with sand. Cuprous chloride and chlorine gas are formed. The latter is utilized and the former reconverted into the cupric salt by treatment with hydrochloric acid and a current of air. The following reactions set forth the process :— CuCl, = CuCI Cl 2CuCI + 0 + HC1 = 20u012 + H20.
The second process was that of Oxland, patented about 1845. He proposed to pass gaseous hydrochloric acid and air, in the proportion of one volume of the former to two of the latter, over pumice stone, bricks, or some other porous substance arranged in a reverberatory furnace, obtaining free chlorine and water.
These processcs were never carried beyond an experimental stage. The first broke down through a certain and inevitable loss of copper ; the second, through producing only a very weak chlorine. Deaoon substituted sulphate for chloride of copper, finding that the decomposition of the hydrochlorie acid is thereby effected at a lower temperature than when the latter salt is employed. His process consists in passing hydr‘rchlorie acid gas, from the salt-cake furnaces, over an arrangement of small clay marbles, broken bricks, coke, or soma other hard but porous substance, saturated with solution of sulphate of copper, and haviug access of air. At a ternperature of about 700° F. the hydrochloric acid is decomposed, with the formation of water and evolution of free chlorine. Mixing sulphate of sodium with the sulphate of copper has been found to facili
tate the operation. The most important point in the process is the regulation of temperature. Below 500° the decomposition does not readily take place ; above 800° volatilization of the chloride of copper which is formed ensues. When the operation is carefully performed and no loss of chloride by volatilization allowed, the sulphate of copper reruains practically unchanged, and tho whole of the chlorine of the hydrochloric acid becomes, theoretically, available for the manufacture of bleaching powder. The chief part of the apparatus is the " decomposer." This consists of a aeries of nine towers constructed of iron, and arranged in somewhat similar style to the Hargreaves cylinders, shown in Fig. 240. The first two towers are packed with bricks or drain pipes, with as open flue spaces as possible ; the remainder are filled with small clay marbles, broken bricks, or coke, arranged above a grating. These materials are thoroughly soaked with the mixed solutions of sulphate of copper and sulphate of sodium. Preceding the decomposer is the " regulator," a brick or iron tower packed with bricks, up which the gases are passed before entering the decomposer. The object of the regulator is simply to ensure a constant temperature. Both regulator and decom poser are surrounded with a strong brickwork casing, in which aro arranged vertical flues, communi cating with a suitable furoaea. To carry out this, the most important, part of the operation successfully, it is of the utmost importance that the decomposer be constructed of the hest possible material and with every .eare. The gases are drawn through the regulator and decomposer by means of .any convenient apparatus—a good chimney draught, or a Roots blower, 8re.—a register of temperatures being made by a pyrometer. and samples of the gases entering and leaving the decom poser being readily obtainable by inserting a finger pump into the pipes and drawing a known quantity through an alkaline solution coloured blue with litmus. A considerable amount of dust— chiefly oxide and ehloride of iron from the pipes or decomposing pans—eollects in the cylinders, falls through the grating into the receptacles at the bottom of the towers, and is periodically cleared away. A more or less imperfeet decomposition is effected, the gases leaving the decomposer con sisting of chlorine, hydroehlorie acid, nitrogen, uuconsumed oxygen, and steam. By regulation of the draught and proper admission of air, great care is taken to reduce the amount of escaping hydrochloric acid to a minimum. These products are next passed up a condenser, whereby the hydrochloric acid is washed out, and then up a coke tower, where they are dried by coming in con tact with strong sulphuric acid. Occasionally a chloride of calcium drier is also resorted to. The gas is now ready to act upon the lime. Owing to the enormous volume to be dealt with, the chambers are constructed in a different fashion from the ordinary bleaching-powder chamber. Outwardly they resemble the old flag or slate boxes, but the interior is divided into a number of compartments, and these are again interseeted with a series of shelves, only about 9 io. space being left between each. Upon these shelves the carefully prepared lime is placed in thin layers, I in. in thickness, and the gas is drawn from shelf to shelf and compartment to compartment, first over the lime most saturated with chlorine, then over that freshly charged. As each division, by testing a sample drawn, is ascertained to be brought up to strength, it is shut off, and the finished bleaching powder raked out.