APPARATUS FOR SEMIMICRO FILTRATION1 JACOB CORNOG and FLOYD 0. IiRAUSE
The State University of lowu, lo-
A NUMBER of methods have been suggested for separating precipitates from filtrates on a semimicro scale. This paper reports some of them that have been tried by the authors. Much of the apparatus is unavailable on the market and must be improvised. We have given names of firms from whom some of the pieces may be purchased, with 1941 prices. The methods are grouped nnder the three general headings: gravity filtration, suction filtration, and pressure filtration. 1. G a d y Filtration. Apparatus required: 1 Micro glass funnel (Fisher Scientific Company, Pittsburgh. Pennsy.vania. Catalog No. 20-700, 35 cents each). 1 Pkg. filter paper 4.25-cm. diameter (Whatman #1 Qualitative filter paper. Central Scientific Company. Chicago, Illinois. 15 cents pkg.).
This is conventional filtration on a small scale. Larger funnels and filter paper may be used, but effectiveness decreases as size increases. 2. Suction Filtration. Some form of small side-arm suction flask is needed for all of the alternatives mentioned under this heading. The authors have found the 13-mm. by 130-mm. side-arm test tube quite satisfactory (George T. Walker and Company, Minneapolis, Minnesota. Catalog No. A56-710, 22 cents each). Alternative (a) uses the side-arm test tube with the micro funnel and filter paper mentioned nnder I. The opening in the apex of the funnel is so small that suction will not rupture the unsupported filter paper. The authors personally prefer this assembly to those below. Alternative (b). This scheme is the same as 2(a) except for the use of a small porcelain Buchner or Hirsch funnel (Central Scientific Company, Chicago, Illinois, No. 22894 Buchner, Coors, Porcelain funnel, 70 cents each. Same firm, No. 22896, Hirsch, Coors,
-
'Excerpt from the forthcoming M S . thesis of Floyd 0. Krause, Chemistry Department. State University of Iowa (1942).
City, Iowo
Porcelain funnel, 50 cents each). This alternative is quite satisfactory except for the fact that filter paper. of the required size cannot be purchased but must be cut individually with cork borers. Alternative (6) is exactly like (a) except that a small square of cloth is folded with the paper, on the outside, so that when placed in the glass funnel the tip of the paper will be protected from rupture by the suction. This is an old expedient in macro-scale suction filtration. 3. Pressure Filtration. Alternative (a).% (All of the apparatus may be purchased from the George T. Walker Company, Minneapolis, Minnesota.) Pressure filter tube (Catalog No. A56-730, 15 eentseach). Vacuum-pressure rubber bulb (Catalog No. A56-740, 25 cents each).
The pressure filter tube is shaped like a centrifuge tube, with a small opening in the bottom and a flared top. A small cotton or glass-wool plug is placed in the small end of the filter tube, which is suspended in a 13-mm. by 130-mm test tube and the liquid forced through the filter by pressure from the bulb. This alternative has the advantage of not requiring suction. Alternative (6) was suggested by H. E. Vermillion, of Beacon, New York. Insert a small cotton plug in the small opening of a medicine dropper, introduce the liquid to be filtered, replace the rubber bulb. Squeezing the bulb forces the liquid through the cotton filter. Although this is rather a "makeshift" scheme, it is inexpensive and serves many a useful purpose under "emergency" conditions. For example, we have found it very helpful for the removal of the occasional precipitates of low density, such as free sulfur, that do not respond readily to centrifuging. We have personally tried all of the schemes here listed and find that all of them are entirely practical but somewhat slower than centrifuging. 'BARBER,Ind. Eng. Chcm., Anal. Ed., 12, 58 (1940).
Fishermen note: It is reported that synthetic angleworms are being molded out of rubber and filled with paste flavored with fish eggs.
