The Willstatter "Nail" and the Schwinger Microfilter John T. Stock University of Connecticut, Storrs, CT 06269
Decidine to become a scientist a t the aee of 12. Richard ~ i l l s t e t t &11872-1942, went on to a briliiant car& in oreanic chcmistrv. He received the Nohel I'rizr of 1915 for his research on plant pigments (1,2). A filtration device similar to that shown a t (a) in the figure and usuallv termed the Willstatter "Nail", is featured in various mic~rochrmicalpublications (3-91. The device ronsists merelv of u 3040-mm diameter funnel and a flatheaded "nail".~ecausethis is made by heat-softening the end of a glass rod and flattening- by- pressing on a surface . such a s that of a file, the head is never perfectly circular. Accordindv, there is a leakape path between head and funnel. corkb borer is used to & a filter-paper disk a few millimeters larger than the head, so that the leakage path is sealed wnen the disk is moistened. Filtration is accomplished under light suction, the decigram or so of solid being washed down onto the disk. When the point of the "nail" is pressed on a tile the head rises, so that the paper carrying the solid can be retrieved. It is neculiar that none of the references cited auotes anv ofwilisthtter's many papers. Possibly, the naLing of th;? device may he a case of "association by usage." Wyatt, who exhaustively examined t h e l i t e r a t u r e concerning micmfiltration (91, apparently had to accept the opinions of Erdos and Lbsz16 (4) and of Gattermann and Wieland (5) that the device is attributable to Diepolder. Presumably, the originator was Emil Josef Diepolder (1870-1923). He
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obtained his PhD a t Erlaneen in 1894 and operated a orivate laboratory in Fkgensb;rg for many The Schwinger microfilter is constructed of a oarallelsided funnel Gaving a heavy-walled stem with bore of about 2 mm. Such a micmfilter is useful when the amount ofsolid is only a few milligrams. Afilter-paper disk slightly smaller than the outs~dedlameter of the stem is secured between the two portions of the stem by meam ofa rubber tubing sleeve, as shown at t b in ~ the figure. Like the "nail", the Schwineer filter is used under li~lhtsuction. The ~ ~solid ~ ~ collects in &e bore a s a column that can either be rinsed out or ejected by use of a suitable rod. Very little solid remains on the paper, because of the small area of contact. If the liquid is volatile, the solid can be air-dried by attachment of a desiccant tube and continuance of suction. Although there are various references to the Schwinger filter, none yet found gives any clue a s to its history (3, 8-13). Pregl (10) does, however, give the full name, Emil Schwinger, a s the originator. This is not unexpected, because both persons were associated with the University of Graz. Little information has been found concerning Schwinger. Apparently, his only individual publication was a n account of a melting-point apparatus (14). He was w-author of two papers dealing with authraquinone chemistry (15,115). Obstruction of view by the rubber sleeve of the Schwinger filter is unfortunate. Any displacement of the tiny disk during assembly will escape detection: unless the amount is large, the coliected solid cannot be seen. Suggestions to improve viewing are the replacement of rubber by transparent plastic tubing (17) or the use of a n outer glass guide tube that is secured to the respective portions of the stem bv rubber sleeves (18).I n another modification. shown a t the cut ends of the stem are expanded to a diameter of approximately 12 mm,a s shown a t (d) (19). The tensioning device is merely a short length of rubber tubing, the middle of which has two horizontally-opposed holes that have been cut with a corkborer. To insert the disk, or to recover the solid after filtration. the device is merelv snapped open, a s shown a t (e).
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Literature Cited 1. Huisgen,R. J.Chem. Edue. lsB1,38,10-15. 2. Robinson,R.J Chem. Soe 19.53.99M026. 3. Clark, S. J. Quontloti"e Method4 o,for#an.nieMiem-.nd~sia;B"ttemttemrth: h d o n , 1956,p 19. 4. Erdbs, J: L b z l d , B. Mikroehm. uer. Mikmch~m.Acfo 1939,27,212215. 5. Cattermann, L.; Wieland. H. Die P m i s dpa or#aniaehen Chemikers; De Gruyter:
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m7 .:1; (d)
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(a) Willstatter "nail"; (b) Schwinger microfilter; (c), (d), (e) "Snapooen" microfilter and details.
822
Journal of Chemical Education
.. ~ubstommeng&;S p l i n g e r ~ & l a gVienna, 1930,p 3. 7. Sehneider,F.L. QualitariuaOrg.nie M i i i i i l y ~ r S . A ~ a d d ~ r m : N ~ w 1964.~56. Y~rk 8. Stock.J. T:Fin. M. A : Robinson. E. A. Intmduelim to Ormnie Chmiatrv. 2nd d.: IJ&&V&"al k s : London, 1967,p 1W. , - ~ ~, 9. Wyatt.0. H.Analyst E M , 71,122-129. 10. Pregl. F Di QuanlifafiveOwanbehe Mikroonolysp; Springer:Berlin, 1930,p 244. n. stock,J . T . I ~~ e t h a i os f ~ v o n t i t o t i ~u i~c m a n d y s l 8h, d d . ~ i l t o n ,F~; watete, . W A . Eds; Arnold: London. 1955.p26. 12. Ref 7,p 54. 13. Ref 8.p 242. 14. Sehwinger, E. Monafsh. 1914.34,977-979. 15. Scholl, R.; khwinger, E. Berich* 1812,44,2992-2998. 16. SchoU, R.; Schwinger, E.; Dischendorder, 0.Berichre 1919,52,2254-2261. 17. Beroaa.M.Cheml8tdnolyat 1851.41,18. 18. Stock,J. T;FiU, M. A. J. Chem Ed- 1964.31,144-148. 19. Stock,J. T.;Fill, M. A. Lob. P~actlco(London) 1857,6,3839. ~~
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