during the process the mass becomes agglomerated, and the final product
is what is known as a "black-ash ball," consisting chiefly of crude
sodium carbonate and calcium sulphide, but containing smaller quantities
of many other substances. The soda ash or sodium carbonate is obtained
from the black ash by lixiviating with water, and after various
purification processes, the solution is boiled down, as previously
stated, by the waste heat of the black-ash furnace. The alkali is sold
in various forms as soda ash, soda crystals, washing soda, etc.

Caustic soda is manufactured from solution of carbonate of soda by
causticising, that is, treatment with caustic lime or quicklime.

It will have been noticed that one of the chief reagents in the Leblanc
process is the sulphur used in the form of brimstone or as pyrites for
making vitriol in the first stage; this sulphur goes through the entire
process; from the vitriol it goes to form a constituent of the
salt-cake, and afterwards of the calcium sulphide contained in the black
ash. This calcium sulphide remains as an insoluble mass when the
carbonate of soda is extracted from the black ash, and forms the chief
constituent of the alkali waste, which until the year 1880 could be seen
in large heaps around chemical works. Now, however, by means of
treatment with kiln gases containing carbonic acid, the sulphur is
extracted from the waste in the form of hydrogen sulphide, which is
burnt to form vitriol, or is used for making pure sulphur; and so what
was once waste is now a source of profit.

_Ammonia-Soda Process of Alkali Manufacture._--This process depends
upon the fact that when carbonic acid is forced, under pressure, into a
saturated solution of ammonia and common salt, sodium bicarbonate is
precipitated, whilst ammonium chloride or "sal-ammoniac" remains