7.1 Weigh to the nearest 0.001 g, 2.5 g of the prepared sample and put it in a 250 ml graduated flask (5.1). Add a little of Petermann’s solution (4) at 20°C, shake very hard in order to stop the formation of lumps and to prevent any of the substance adhering to the side of the flask. Make up to the mark with Petermann’s solution and close the flask with a rubber stopper.
Shake for two hours on the rotary shaker (5.2). Filter immediately through a dry fluted filter, into a dry container, discarding the first portion of the filtrate.