In order to hasten the precipitation of the ammonium magnesium
phosphate and to prevent the fixation of the precipitate on the walls
of the erlenmeyer, the flask should be shaken for half an hour. For
this purpose the flasks should be closed with smooth well-fitting
rubber stoppers and placed in a shaking machine. The shaking machine
of the form given in Fig. 4, recommended by the Halle station, is very
conveniently used for this purpose.
On a vertical axis are carried two stages for holding the flasks.
The flasks are prevented from striking each other by means of the
partitions shown. The apparatus is conveniently driven by a small
water-motor, as indicated, which imparts to the stages a partial back
and forth revolution.
After shaking for half an hour, any precipitate adhering to the rubber
stoppers is carefully washed off with ammonia water into the flask. The
filtration can be made immediately after the shaking or after two or
three days; the results are the same.
[Illustration: FIGURE 5.