Buchner funnel

In the so-called “Buchner funnel,” the filtering vessel is cylindrical, and the paper receives support by being laid upon its flat perforated bottom.

It is cooled in a freezing mixture and then either centrifuged or filtered on a large Buchner funnel, washed with water until the washings are neutral to litmus, and finally washed with 200 cc. of alcohol, which has previously been cooled to 0'0.

The mass of crystals is then rapidly filtered on a Buchner funnel and sucked as dry as possible.

In transferring the crystals from the reaction flask to the Buchner funnel it is necessary to use a certain amount of water to dissolve the pasty chromium salts which are otherwise quite impossible to filter.