7 specimens illustrating the manufacture of soda, in bottles:- (a) common salt (b) salt cake (c) limestone (d) slack (e) black ash (f) salts (g) soda ash

These early specimens show the raw materials used and the products obtained in the two stages by which Sodium Carbonate, or ordinary washing soda, is manufactured from common salt by the Leblanc process.

The first stage of the process consists in heating common salt with sulphuric acid to form salt cake, or Sodium sulphate. In the second stage, the salt cake is heated with limestone and small coal for the production of black ash. This is lixiviated with water, producing a saturated solution of soda known as vat liquor which, on boiling down, deposits crude Sodium Carbonate Crystals, from which commercial soda is formed.