Sodium Sulfate Anhydrous — Frequently Asked Questions

It drives dye onto the fibre, a process called exhaustion. Reactive and direct dyes and cellulose fibres both carry negative charge in the dyebath and therefore repel each other, so much of the dye stays in solution. Adding sodium sulfate raises the ionic strength, screening that repulsion so the dye transfers onto the fibre, which deepens the shade and reduces dye left in the effluent.

Because inertness is the point. In powder detergents it occupies volume, keeps the powder free-flowing and carries the active ingredients without reacting with them or affecting performance, at very low cost. A filler that participated in the chemistry would be a liability. Its neutrality, low cost and non-hygroscopic nature are exactly what the role requires.

It acts as a fining agent, helping remove bubbles and scum from the molten batch. It decomposes in the melt to release gas that helps sweep out entrained air, and it reduces the formation of scum on the glass surface. Small quantities have a disproportionate effect on the clarity of the finished glass.

Not in the way that many salts are; it is comparatively stable in air, which is part of why it works as a free-flow agent in powders. It will, however, take up water to form the decahydrate under damp conditions, and that transition involves a volume change, so it should still be stored dry and sealed.