Division 3.7 Place the partially dried samples in a vacuum drying oven, with the dishes resting directly on the shelf.

Allow dry air to enter the oven, passing through the H₂SO₄ purifier at a rate of two to four bubbles per second.

Dry the samples for four hours at 70 °C and at a pressure not exceeding 50 mm Hg.

The oven temperature may be as low as 65 °C when drying begins, but must rise to between 69 and 71 °C within the first hour.