sulphurous acid

Thus far the value of the products obtained by absorption of sulphurous acid has not been equal to the cost of producing them.

Sulphurous acid can fulfil in this instance a double function, viz.

The gum is dissolved in water, and sulphurous acid gas passed through the solution.

Hence the necessity of having a little free sulphurous acid in each tube.

The colour, however, is not removed by boiling or by sulphurous acid.