The crystals are collected, washed, pressed and recrystallized, whereby the impurities are easily removed.
It can be recrystallized by solution in alkalies.
The disulphonate is more readily obtained by moistening the nitrilosulphonate with dilute sulphuric acid and letting it stand for twenty-four hours, after which it is recrystallized from dilute ammonia.
The solutions are made by dissolving the purest recrystallized sulphate of copper and sulphate of zinc in distilled water.
This is distilled to dryness and the distillate repeatedly recrystallized from cymene.