SODA, CARBONATE OF 



857 



must be raked out into cast-iron moulds, placed under the door of the laboratory to 

 receive the ignited paste. 



One batch being thus worked off, the other, which has laid undisturbed on the 

 shelf, is to be shoved down from A to B, and spread equally upon it, in order to be 

 treated as above described. A third batch is then to be placed on the shelf. 



The product thus obtained is called ' black balls,' which, of course, vary in their 

 composition. The following is the composition, according to Kichardson, of the 

 Newcastle ' black balls,' from the balling furnaces : 



Carbonate of soda 9 P 89, hydrate of soda 25"64, sulphide of calcium 35'57, carbonate 

 of lime 15'67, sulphate of soda 3'64, chloride of sodium 0-&0, sulphide of iron 1'22, 

 silicate of magnesia 0'88, carbon 4'28, sand - 44, and water 2 - 17 = 100. 



The principal changes which take place in this process may be represented by the 

 following equations : 



NaO.SO 8 



then 



CaCO 8 



NaS 



TJa-S 



= NaO.CO 2 + 



Wa 2 C0 3 



4CO 



CaS). 



In the first place, the sulphate of soda is deoxidised by the coal, with the formation of 

 .sulphide of sodium and carbonic oxide, which latter takes fire and forms the ' candles,' 

 above mentioned ; in the next place, the sulphide of sodium and carbonate of lime 

 (chalk) decompose each other, forming carbonate of soda and sulphide of calcium ; 

 and from the fact of some of the chalk being converted into caustic lime by the heat 

 of the furnace, there is also formed by it some caustic soda ; the sulphide of cal- 

 cium itself is only sparingly soluble in water, but is rendered still less so by the excess 

 of lime which is present, forming with it an oxysulphide, which is much less soluble 

 than the sulphide of calcium alone. 



This black ball, or ball alkali, is then treated with warm water to extract the soluble 

 .matters. This is effected in the district of Newcastle-on-Tyne in vessels, 8 or 10 feet 

 square and 5 or 6 feet deep, furnished with false bottoms ; the first waters are strong 

 enough for boiling down, for getting ' yellow salt,' as it is termed ; the after-washings, 

 which are weaker, are used for fresh quantities of ' ball alkali.' Care must be taken 

 .not to use the water too hot, as the oxysulphide of calcium would be decomposed, and 

 the liquor thus take up much sulphide of calcium. 



1859 



An apparatus used in some places for lixiviating the black ball is shown in the 

 accompanying drawing, fig. 1859. Its object is to extract the largest quantity of 

 soluble matter with the smallest quantity of water. The black ball is placed in per- 



