A Simple Pressure Filter A. WEXLER
L.C.C. Hackney Technical Institute, London, England
N RESPONSE to a sudden demand in this laboratory for large numbers of pressure filters a t very low cost, the form described was designed. The essential feature of interest is the 'use of a bed of chips of broken glass or porcelain to support the asbestos fiber, instead of a perforated plate as is used, for instance, in the Gooch crucible. This scheme has in fact proved rather more versatile in application than was originally expected, and it is therefore hoped that the forms shown in the accompanying diagrams may prove of some use to chemists, and may also suggest other variations.
can be held in stock fully prepared and dried, and also tared if necessary. WNMCTION TO WESSURE .LINE
-GASKET SCREW CAP
-METAL
TUBE
1/4'
WALLS
FILTER
PULP
GLASS CHIPS
RUBBER STOPPER
FIGUR~2
..
..
(2) The filter requires no special funnel for support. as does the Gooch crucible. PRESSURE TUBING GLASS TUBE
Figure 1 shows the simple type of+pressure filter for use with the exhaust pump. The tube A is readily made by drawing out glass tubing or a test tube, preferably of resistance glass. One or two larger pieces of glass are first lodged in the neck N and enough smaller st& is then added to make a level bed. The prepared asbestos pulp is then added in a thin stream in a quan. tity suited to the nature of the precipitate to be filtered, and the filter is well flushed in the usual way until the filtrate is clear of fibers. Dimensions can of course be varied in accordance with requirements. Filters of this type, weighing about one gram, and useful for micro work, can be readily made from thin-walled tubing of approximately 3/s-inch diameter. For general use, stouter tubes a/d inch or more in diameter will be found more suitable. Certain advantages of this simple device, perhaps not immediately obvious, are: (1) The filter can be made in the laboratory in a few minutes, and the cost is so small that large numbers 167
RUBBER STOPPER WIRED
ON
WIRE GAUZE
SIRUP TO BE FILTERED
-
LARGE TEST TUBE
ADSORBENT MATERIAL ASBESTOS PULP GLASS CHIPS
FIGURE3
(3) Vacuum drying of the precipitate may be very and 3 indicate two dBerent schemes for achieving higheasily effected by making a connection directly to the pressure filtration. In using the arrangement indicated pump via the stem S, closing the opening 0 with a stop- in Figure 2 it is essential to have a reliable reducing per, and gently warming. valve from the gas cylinder, and also a pressure release Because of the shape of the apparatus, it is easy valve and connection to the filter must be made with (4) to arrange for heating the precipitate in a current of a high-pressure tubing and screw-on nipples. In the argas. (Ezample: Gravimetric estimation of a mixture rangement shown in Figure 3 the pressure is generate4 of two halides by weighing the silver salts together and internally by careful application of heat to the tube via then finding the weight of the silver after reduction with the roll of wire gauze in which it is wrapped. Due care hydrogen.) and judgment are necessary in the use of this device, By using a high-resistance glass, sufficiently high in view of the contingency of the blow-off valve failing temperatures for ignition, for most purposes, can be to function. The writer, who has used this device with safely applied. Good results were obtained, for in- some success for filtering thick simps mixed with adstance, with Fe and Al precipitates. sorbents, has been in the habit of operating with the Occasions arise in which pressures much higher than tube well back of the fume chamber, with the window fifteen pounds per square inch are needed for the filtra- almost closed for protection. tion and in which the quantities are too small to put For many purposes paper pulp can be used instead of through the laboratory plate filter press. Figures 2 asbestos.
