Preparation of potassium permaganate

(the section title prints "Preparation of potassium permaganate" — the book's own spelling of permanganate; kept verbatim in the heading, spelt correctly in this text)

i. Chemical oxidation

When a finely divided manganese dioxide ($\mathrm{MnO_2}$) is heated strongly with a fused mass of caustic potash (KOH) and an oxidising agent, potassium chlorate ($\mathrm{KClO_3}$), dark green potassium manganate, $\mathrm{K_2MnO_4}$, is formed.

In neutral or acidic medium the green potassium manganate disproportionates to $\mathrm{KMnO_4}$ and $\mathrm{MnO_2}$.

The liquid is filtered through glass wool or sintered glass and evaporated until crystallisation occurs. Potassium permanganate forms small crystals which are almost black in appearance.

ii. Electrolytic oxidation

In electrolytic oxidation, an alkaline solution of manganate ion is electrolysed between iron electrodes separated by a diaphragm. The overall reaction is as follows : …