An Elementary Study of Chemistry

by William McPherson; William Edwards Henderson

Na₂SO₃ + S = Na₂S₂O₃.

It is used in photography and in the bleaching industry, to absorb the excess of chlorine which is left upon the bleached fabrics.

Thio compounds. The prefix "thio" means sulphur. It is used to designate substances which may be regarded as derived from oxygen compounds by replacing the whole or a part of their oxygen with sulphur. The thiosulphates may be regarded as sulphates in which one atom of oxygen has been replaced by an atom of sulphur. This may be seen by comparing the formula Na₂SO₄ (sodium sulphate) with the formula Na₂S₂O₃ (sodium thiosulphate).

Sodium carbonate (sal soda)(Na₂CO₃·10H₂O). There are two different methods now employed in the manufacture of this important substance.

1. Le Blanc process. This older process involves several distinct reactions, as shown in the following equations.

(a) Sodium chloride is first converted into sodium sulphate:

2NaCl + H₂SO₄ = Na₂SO₄ + 2HCl.

(b) The sodium sulphate is next reduced to sulphide by heating it with carbon:

Na₂SO₄ + 2C = Na₂S + 2CO₂.