SODA 



remain* till it liecomea sufficiently heated through- 

 out the whole maw. It IK then transferred t<> the 

 Jlujcing bed, B, which ig next the fire, ami exposed 

 to a higher hent, when it shortly begins tn -ni'tcii 

 ami flux into a mass like dougli. In aliout tiny 

 minute* the charge is withdrawn in a red-hot state 

 liy the working door, and received into iron burrow*, 



fig. 3. Section of lulling Furnace, showing an evaporating pan, P, P, for Socla- 

 liquor in connection with it. 



where it solidities into blocks of crude soda, termed 

 ball -i ula or black-ash. 



Black-ash is now extensively made in a revolving 

 furnace, which does away with the arduous manual 

 labour required in a stationary furnace, and which 

 was first patented in 1853, though many difficulties 

 had to be overcome before it became a success. Mr 

 J. C. Stevenson, of the Jarrow Chemical Works, 

 after much labour succeeded about 1870 in estab- 

 lishing ite superiority over the older kinds of 

 balling furnaces. A longitudinal section of this 

 furnace is shown in fig. 4. It is either cylindrical 

 or barrel -shaped, alx>ut 18 feet long and 10 feet 

 in diameter, lined with firebrick. The furnace is 

 driven by steam and the necessary gearing, a spur- 

 wheel being placed round and fixed to the cylinder, 

 which turns on friction rollers. At one end it is 



liquor in the one containing fresh black-ash, while 

 tlir ntliiT two have liquors of intermediate but 

 unequal strength.*. Tin- level of the liquor differs 

 in each, being highest where weakest and lowi-t 

 w hern strongest. When communication is opened 

 between these tanks circulation i- can-ed l>y hydro- 

 static pressure. The soda liquor from the black- 

 ash is treated differently, 

 according to whether soda- 

 ash or caustic-soda is to be 

 made from it. 



fustic-soda. As the 

 tank liquor consists of a 

 strong solution of carbonate 

 of soda, it requires to be 

 diluted liei'ure it can be 

 causticised with lime. Long 

 iron cylinders contain this 



diluted Honor, into wliich 



. * ' . ... 



Fig. 4. Revolving Black-ash Furnace, partly in section : 



F, Ore ; R, revolving cylinder ; W, friction wheel* ; II, Unks, 4c., 



for evaporating gotla-lye by waste heat of furnace. 



furnished with a large fireplace, the fire gases from 

 which pass through the 'barrel,' and onwards to 

 heat the boiling-down pans, which are placed at 

 the opposite end and arranged much in the same 

 way as in the stationary furnace. The larger- 

 sized revolving furnaces produce 30 tons of black- 

 ash in twenty-four hours. 



I.tximiitiim of the Black-ash, The crude soda 

 so named requires to be porous, HO that water will 

 easily penetrate the broken lumps of it when placed 

 in iron tanks. Formerly a series, say of four of 

 these, was placed in a step-like arrangement in 

 which the lowest contained the fresh black-ash 

 and the highest that which was nearly exhausted 

 of its soda. Fresh water flowed in at the top, and, 

 a it dissolved out the soda, became gradually 

 stronger in descending from tank to tank, till it 

 reached its full strength in the lowest one. A 

 more recent plan is to nave the tanks all on a level 

 and communicating with each other by tulies ; but 

 the exhaustion of the black-ash takes place in a 

 similar way. Weak soda liquor is present in the 

 tank with the nearly exhausted ash, and strong 



lime is placed, and at the same time it is heated 

 and agitated. After being allowed to settle, 

 the clear liquor is drawn off ainl |nim|K>d into 

 liquor settlers, the lime mud in these being saved 

 and used in the black-ash furnace. Several iron 

 concentrating cisterns are successively used \\itli 

 the aid of heat to bring up by degrees t lie canst icised 

 soda liquor to the required strength. From the 

 last of these cisterns (boat-pans) the liquor, having 

 a specific gravity of 1-550, is run into cast -iron pots, 

 each of a capacity of 10 tons, which are heated by 

 strong fires, and here the concentration of the liquor 

 is completed, and the caustic-soda ladled into sheet- 

 iron 'drums' containing 6 ewt. each. On cooling 

 it solidifies into a white mass of sodium hydrate 

 or caustic-soda, NaOH, which is now manufactured 

 in large quantities, containing as much as 77 per 

 cent, of sodium monoxide, NaO. During the con- 

 centration nitrate of soda is used to decompose any 

 sodium sulphide present in the liquor. Caustic- 

 soda is most largely used in soap-making and 

 paper-making, but also in the manufacture of 

 some coal-tar dyes and oxalic acid. 



Soda-ash. When this substance 'carbonate of 

 soda) and not caustic-soda is to be made, the 

 black-ash liquor is differently treated. In referring 

 to the black-ash furnaces (see figs. 3, 4) it has been 

 stated that their waste heat is used to Imil down 

 the black-ash liquor. As the concentration of the 

 liquor proceeds granular crystals of soda are 

 deposited and scraped out into drainers. When 

 heated these crystals vield soda-ash ; but impure 

 soda remains in the ooiling-down vessel. This 

 soda, which is mostly carbonate but also contains 

 caustic-soda and sodium sulphide, is mixed with 

 some sawdust and evaporated to dryness. The 

 black-salt, as this residual substance' is called, is. 

 then heated in a carbonating oven in which the 

 burning oil' of the sawdust generates ,-ailionic 

 acid, and this converts the caustic-soda and 

 sodium sulphide present into carlionnte, and soda- 

 ash is the result. The comiHisition of commercial 

 soda-ash is very variable, but it frequently con- 

 tains about 80 per cent, of the carbonate, the 

 remainder consisting of other com]Hinnds nf sodium 

 and small quantities of other substanc.--. None of 

 these, however, interfere with ite use for the 

 purposes for which it is usually employed. When 

 it is sold the available percentage of s'oda (sodium 

 oxide or NaO) is quoted. For certain purpose* 

 soda-ash is refined by dissolving, settling, evaporat- 

 ing, and calcining. It is then called ivfturd or 

 white alkali, which should be free of caustic-soda 

 and contain no trace of sodium sulphide, sodium 

 sulphite, or of iron. 



Crystals of Soda, H'athintj-miitii, Na.COj.lOHiO. 

 The soda ash used for making soda crystals is pre- 

 viously calcined and dissolved in hot water in iron 

 vessels, the solution being then allowed to cool 



