Hirsch funnel, with polyethylene

FIG. 4 Hirsch funnel with integral adapter, polyethylene frit, and 25 mL filter flask. 

Hirsch funnel fits into the filter fiask with no adapter, and is equipped with a polyethylene frit for removal of the crystals (Fig. 4). For larger quantities of material, porcelain or plastic Buchner funnels are used with pieces of filter paper that fit the bottom of the funnel. A filter adapter is used to form a vacuum tight seal between the flask and the funnel (Fig. 5). 

The Williamson/Kontes Hirsch funnel is unique. It is made of polypropylene and has an integral molded stopper that fits the 25-mL filter flask. It comes fitted with a 20-micron polyethylene fritted disk, which is not meant to be disposable (Fig. 7). While products can be collected directly on this... 

Two types of funnels are useful for vacuum filtration, the Hirsch funnel and the Buchner ftmnel. The Hirsch funnel is used for filtering smaller amounts of solid from solution. Hirsch funnels are usually made from polypropylene or porcelain. The polypropylene Hirsch funnel (see Figure 8.5A) is sealed to a 50-mL filter flask by a small section of Gooch tubing. This Hirsch funnel has a built-in adapter that forms a tight seal with some 25-mL filter flasks without the Gooch tubing. A fritted polyethylene... 

Use of the Hirsch Funnel. The standard filtration system for collecting products purified by recrystallization in the microscale laboratory is vacuum (suction) ffltration with an 11-mm Hirsch funnel. Many reaction products that do not require recrystallization can also be collected directly by vacuum filtration. The Hirsch funnel (Fig.5.23a) is composed of a ceramic cone with a circular flat bed perforated with small holes. The diameter of the bed is covered by a flat piece of filter paper of the same diameter. The funnel is sealed into a filter flask with a Neoprene adapter (Fig. 5.23b). Plastic and glass varieties of this funnel that have a polyethylene or glass frit are now available. It is stfll advisable to use the filter paper disk with these funnels to prevent the frit from clogging or becoming discolored. Regardless of the type of fflter used, always wet the filter paper disk with the solvent being used in the crystallization and then apply the vacuum. This ensures that the filter paper disk is firmly seated on the bed of the filter. 

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