June 20, 1889] 



NATURE 



i«3 



cess, owing to the alkali being in a fused or perfectly liquid 

 condition in contact directly with carbon, the necessity of this 

 is avoided, and consequently, the reduction can be carried on in 

 large vessels at a comparatively low temperature. The reaction 

 taking place may be exjiressed as follows : — 



3NaH0 + C = Na2C03 + 3H + Na. 



The vessels in which the charges of alkali and reducing 

 material are heated are of egg-shaped pattern, about 18 inches 

 in width at their widest part, and about 3 feet high, and are 

 made in two portions, the lower one being actually in the form 

 of a crucible, while the upper one is provided with an upright 

 stem and a protruding hollow arm. This part of the apparatus 

 is known as the cover. In commencing the operation, these 

 covers are raised in the heated furnace through apertures pro- 

 vided in the floor of the heated chamber, and are then fastened 

 in their place by an attachment adjusted to the stem ; the hollow 

 arm extends outside the furnace. Directly below each aperture 

 in the bottom of the furnace are situated the hydraulic lifts, 

 attached to the top of which are the platforms upon which are 

 placed the crucibles to be raised into the furnace. Attached to 

 the hydraulic lifts are the usual reversing valves for lowering or 

 raising, and the platform is of such a size as, when raised, com- 

 pletely to fill the bottom aperture of the furnace. The charged 

 crucible, being placed upon the platform, is raised into its posi- 

 tion, the edges meeting those of the cover, forming an air-tight 

 joint which prevents the escape of gas and vapour from the 

 vessel during reduction, except by the hollow arm provided for 

 this purpose. The natural expansion of the iron vessels is 

 accommodated by the water-pressure in the hydraulic lifts, so 

 that the joint of the cover and crucible are not disturbed until it 

 is intended to lower the lift for the purpose of removing the 

 crucible. 



The length of time required for the first operation of reduction 

 and distillation is about two hours. At the end of this time the 

 crucibles are lowered, taken from the platforms by a large pair 

 of tongs on wheels, carried to a dumping pit, and thrown on 

 their side. The residue is cleaned out, and the hot pot, being 

 again gripped by the tongs, is taken back to the furnace. On 

 its way, the charge of alkali and reducing material is thrown in. 

 It is again placed on the lift and raised in position against the 

 edges of the cover. The time consumed in making the change 

 is a minute and a half, and it only requires about seven minutes 

 to draw, empty, recharge, and replace the five crucibles in each 

 furnace. In this manner the crucibles retain the greater amount 

 of their heat, so that the operation of reduction and distillation 

 now only requires one hour and ten minutes. Each of the four 

 furnaces, of five crucibles each, when in operation, are drawn 

 alternately, so that the process is carried on night and day. 



Attached to the protruding hollow arm from the cover are the 

 condensers, which are cf a peculiar pattern specially adapted to 

 this process, being quite different from those formerly used. 

 They are about 5 inches in diameter and nearly 3 feet long, and 

 have a small opening in the bottom about 20 inches from the 

 nozzle. The bottom of these condensers is so inclined that the 

 metal condensed from the vapour issuing from the crucible 

 during reduction, flows down and out into a small pot placed 

 directly below this opening. The unc6ndensed gases escape 

 from the condenser at the further end, and burn with the cha- 

 racteristic sodium flame. The condensers are also provided 

 with a small hinged door at the further end, by means of which 

 the workmen from time to time may look in to observe how the 

 distillation is progressing. Previous to drawing the crucibles 

 from the furnace for the purpose of emptying and recharging, 

 the small pots each containing the distilled metal are removed, 

 and empty ones substituted. Those removed each contain, on 

 an average, about 6 pounds of metal, and are taken directly 

 to the sodium casting shop, when it is melted and cast, either 

 into large bars ready to be used for making aluminium, or in 

 smaller sticks to be used. 



Special care is taken to keep the temperature of the furnaces 

 at about 1000° C, and the gas- and air- valves are carefully re- 

 gulated, so as to maintain as even a temperature as possible. 

 The covers remain in the furnace from Sunday night to Saturday 

 afternoon, and the crucibles are kept in use until they are worn 

 out, when new ones are substituted without interrupting the 

 general running of the furnace. A furnace in operation re- 

 quires 250 pounds of caustic soda every one hour and ten 

 minutes, and yields, in the same time, 30 pounds of sodium 

 and about 240 pounds of crude carbonate of soda. With the 



four furnaces at work, 120 pounds of sodium can be made every 

 seventy minutes, or over a ton in the twenty-four hours. The 

 residual carbonate, on treatment with lime in the usual manner, 

 yields two thirds of the original amount of caustic operated 

 upon. The sodium, after being cast, is saturated with kerosene 

 oil, and stored in large tanks holding several tons, placed in 

 rooms specially designed both for security against either fire or 

 water. 



ChloHne Manufaclnre. 



This part of the works is connected with the adjacent works 

 of Messrs. Chance Bros, by a large gutta percha pipe, by means 

 of which, from time to time, hydrochloric acid is supplied direct 

 into the large storage cisterns, from which it is used as desired 

 for making the chlorine. For the preparation of the chlorine 

 gas needed in making the chloride, the usual method is em- 

 ployed ; that is, hydrochloric acid and manganese .dioxide are 

 heated together, when chlorine gas is evolved with effervescence, 

 and is led away by earthenware and lead pipes to large lead- 

 lined gasometers, where it is stored. 



The materials for the generation of the chlorine are brought 

 together in large tanks or stills, built up out of great sandstone 

 slabs, having rubber joints, and the heating is effected by the 

 injection of steam. The evolution of gas, at first rapid, becomes 

 gradually slower, and at last stops ; the hydrochloric acid and 

 manganese dioxide being converted into chlorine and manganous 

 chloride. This last compound remains dissolved in the "spent 

 still liquor" and is reconverted into manganese dioxide, to be 

 used over again, by Weldon's manganese recovery process. 

 Owing to the difficulty of keeping up a regular supply of chlorine 

 under a constant pressure directly from the stills, in order that 

 the quantity passed into the sixty diflerent retorts in which the 

 double chloride is made can be regulated and fed as desired, 

 four large gasometers were erected. Each of these is capable 

 of holding 1000 cubic feet of gas, and is completely lined with 

 lead, as are all the connecting mains, &c., this being the only 

 available metal which withstands the corrosive action of chlorine. 

 The gasometers are filled in turn from the stills, the chlorine 

 consumed being taken direct from a gasometer under a regular 

 pressure until it is exhausted ; the valves being changed, the 

 supply is taken from another holder, the emptied one being 

 refilled from the still. 



Manufacture of the Double Chloride. 



Twelve large regenerative gas furnaces are used for heating, 

 and in each of these are fixed five horizontal fire-clay retorts about 

 10 feet in length, into which the mixture for making the double 

 chloride is placed. These furnaces have been built in two rows, 

 six on a side, the clear passage-way down the centre of the 

 building, which is about 250 feet long, being 50 feet in width. 

 Above this central passage is the staging, carrying the large 

 1 jad-mains for the supply of the chlorine coming from the gaso- 

 meters. Opposite each retort, and attached to the main, are 

 situated the regulating valves, connected with lead and earthen- 

 ware pipes, for the regulation and passage of the chlorine to 

 each retort. The valves are of peculiar design, and have been 

 so constructed that the chlorine is made to pass through a certain 

 depth of liquid, which not only, by opposing a certain pressure, 

 allows a known quantity of gas to pass in a given time, but 

 a'so prevents any return from the retort into the main, should an 

 increase of pressure be suddenly developed in the retorts. 



The mixture with which the retorts are charged is made by 

 grinding together hydrate of alumina, salt, and charcoal. This 

 mixture is then moistened \\ ith water, which partially dissolves 

 the salt, and thrown into a pug mill of the usual type for making 

 drain pipes, excepting that the mass is forced out into solid 

 cylindrical lengths upon a platform alongside of which a work- 

 man is stationed with a large knife, by means of which the 

 material is cut into lengths of about 3 inches each. These are 

 then piled on top of the large furnaces to dry. In a few hours 

 they have sufficiently hardened to allow of their being handled. 

 They are then transferred to large waggons, and are ready to be 

 used in charging the retorts. 



The Success of this process is in a great measure dependent — 

 (i) on the proportionate mixture of materials •. (2) on the tem- 

 perature of the furnace ; (3) on the quantity of chlorine intro- 

 duced in a given time ; and (4) on the actual construction of the 

 retorts. I am, however, not at liberty to discuss the details of 

 this part of the process, which have only a commercial interest. 

 In carrying on the operation, the furnaces or retorts, when at the 

 proper temperature, are charged by throwing in the balls ur til 



