Kipp's apparatus with powders A Kipp's apparatus has three distinct bulbs. The topmost one contains a liquid and a tube to the bottommost one. The middle one contains a solid to react with the liquid.



This is very understandable when large chunks of solid are used. However, what do people do when they need to react a powder (e.g. sodium sulfite)? It seems that the powder would just fall through and keep reacting when the valve is closed.
According to the Wikipedia page on the Kipp's apparatus, if the reactant is a powder, and soluble in water, you can soak pieces of pumice in the solution, dry the pumice, and use it in a Kipp's apparatus. There is also a variant of the apparatus that allows two liquids to be used together rather than a liquid and a solid reactant. In that case, you would pre-dissolve the sodium sulfite in water.