edited bv GEORGEL. GILBERT Denison University Granville. Ohio 43023
the blue Fugates would say, "I can just see that old blue running out of my body!' It seems paradoxical to use a blue dye to remove that same color from the skin. but it can he ex~lainedon the basis of the electron transfer properties of mdthylene blue.3 The dye is first reduced to its colorless form hv vvridine nucleotides (eq 2). It is then oxidized back to its blueform by methemoglobin (eq 3). Thus in the latter reaction methylene blue fulfills the role played hy diaphorase in normal blood.
A Well-Known Chemical DemonstrationTo Illustrate an Unusual Medical Mystery SUBMITTEDBY
Arlel E. Fenster
Vanler College Montreal, PO H3X 2N9, Canada Davld N. Harpp
McGlll Unlverslty Montreal. PO H3A 2K6, Canada Joseph A. Schwarcz
methylene blue (blue) methylene blue + methernoglobin
Vanler College Montreal, PO H3X 2N9, Canada CHECKEDBY
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-
methylene blue (colorless)
(2)
James 0. Glanvllle Virglnia Tech
Blacksburg, VA 24061
Chemical demonstrations represent an essential tool in the teaching of chemical principles. However, i t is often difficult to relate these demonstrations to actual applications. Thus, we would like to report our use of the wellknown "hlue shaking dye" demonstration1 to accompany a very unusual medical case, that of the blue people of Troublesome Creek.2 Over the last 150 years or so many inhabitants of this isolated Kentucky valley puzzled the medical world by exhibiting skin complexions in various shades of blue. The mystery was solved a few years ago by Madison Cawein. The problem was caused by a recessive gene brought to the area some six generations before by a French immigrant, Martin Fueate. . and his American-born wife. Elizabeth Smith. Normally in the blood, oxygen-carrying hemoglobin is in the ferrous state: it readilv oxidizes to the ferric state vielding methemoglohiu, which is inactive as far as oxygen transport is concerned. Fortunatelv. this process is reversed bv an inzyme, diaphorase, which r;ducrs'methemuglobin back to hemoalubin lea 1 I . In thecaseofthe "blue Fuaatcs",as these people were known, the gene caused relativeiy lowlevels of diapborase thus increasing the concentration of methemoglobin, which when viewed through the skin gives a hlue appearance. 0%
hemoglobin Hb(Fe2+)
c oxyhemo lobin
~ b ( ~ e- O2 +4
(1)
An appropriate system that nicely illustrates this idea is the blue shaking dye demonstration.' About 10 g of KOH and 8 g of glucose are dissolved in 400 mL of water in a 1-L Erlenmever flask. A few milliliters of 1%methvlene blue is added, and upon standing the solutiun turns colorless indicatina that thedve has h e n reduced by thealucose. Shakina the fiask will then cause the blue color to return as the methylene blue is oxidized (in this case by atmospheric oxygen) to its blue form as it would be by the methemoglobin in the case of the blue Fugates. The demonstration can he repeated as long as there is enough glucose present to reduce the methylene blue. We have found that our students " ereatlv. eniov . "the storv and the associated demonstration; it offers a good example of the importance of electron transfer reactions in bioloeical processes. Acknowledgment
We acknowledge helpful discussions with Witold Rybka, Montreal General Hospital, 1650 Cedar Ave., Montreal, PQ H3G 1A4.
Shedding a New Light on Solubility Calculations SueM~moBY
Rlchard J.Stolzberg
Unlverslty 01 Alaska
Fairbanks, AK 99775
methemoglobin Hb(FefS) Understanding the cause of the problem provided Cawein with a treatment for this unusual condition. The Fugates saw the blue color of their skin replaced by a more usual pink as long as they kept taking daily pills of methylene blue. There was, however, a colorful side effect upon urination;
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Chen. P. S. Entertaining and Educational Chemical Demonstra ti0ns:Chernical Elements: Camarillo. CA. 1974. The Science Almanac. - ~ -1985-1986 , ~-~ ed. Anchor: New Yark. . ~,1984 - p 446: Mansouri. A. Am. J. Med. Sci. 1985,289, 200, and reference; cited therein: Mack, R. North Carolina Med. J. 1982, 4, 292. Goodman L. S., Gilman. A. The Pharmacological Basis of There peutics, 4th ed. Macrnillan: New York: p 1056 ~
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CHECKED BY
Paul C. Krause
Unlverrlly ol Central Arkansas Conwav. .. AR 72032 Precipitate formation, fractional precipitation, and precivitate dissolution can be investigated in a series of lecture demonstrations suitable for general chemis~r).or quantitativeanalssis. Chlorideand chromatesaltsof silver can du the job. when C1- and Cr042- are present a t the same concentration, virtually all of the C1- can be precipitated with Agf hefore the first AgpCr04(s) is formed. Since Cr042-is a weak base, AgpCrOa can be dissolved by the addition of strong acid.
-
Ag~CrOd(s)+ Ht(aq)
-
2Agt(aq) + HCrOn-(aq)
AgClrs) is unaffected. Hoth precipitates can be dissulved by addition of YH?,which romplexrs the Ag'. Volume 65
Number 7
July 1986
621
M NaCl and 10-3 M K2CrOd Individual solutions of can he used to verify calculations for the volume of 0.1 M AgN03 necessary to form a precipitate. A laser beam passing through the solutions enables the students to observe the first formation of a colloidal precipitate via the Tyndall effect. A mixed solution containing 10-3M NaCl and M KpCr04 can then he used to verify that chloride may he completely separated from chromate via precipitation. An element of charm is introduced when the red AgpCrOa precipitates hefore the AgCI, only to dissolve in a few seconds. Resulting mixtures can then he used to determine how addition of H+ and NH3affect precipitate solubility. Thus, quantitative and qualitative predictions can he made and verified in approximately 0.5 h of class time. Observation of the laser beam scattering is easiest in a small classroom. The demonstration is useful in a large lecture hall, however. In addition, the Ag2Cr04 precipitate formation portion of the demonstration can he used separately as an experimental determination of the AgpCrOa solubility product constant.
10 mL 8 M HN03 10 mL 1 M NH3 10-mL graduated cylinder disposable Pasteur pipet and bulb or micropipet magnetic stir plate and three stir bars He-Ne laser or bright lamp and clamps to position (optional)
Experiment
Joseph H. Drelsbach Unlrerslty o( Scranton
First work through the calculations todetermine the minimum concentration of Ag+ and the minimum volume of 0.1 M AgNOl necessary to begin precipitation when the AgN03 isadded to500 mLof 1.0 X 10." NaCl and toS00mLof 1.0 X 10-:'M K2CrO4ll.9X 10-:M,0.001 mLforCIk4.1 X M, 0.21 mL for CrOa2-). Place the heaker of KzCrOl on the stir plate with the laser beam uassine verticallv throueh the solution. (Caution: Have students close their eyes before turning on laser. Verify that reflections do not go toward the audience.) Add AgN03 dropwise with a Pasteur pipet (0.03 mL/drop) or a micropipet from 5 mL of solution in a graduated cylinder. A red precipitate will form and dissolve with each drop. The permanent preci~itatecan he observed by scattered light after 7 drops ( 6 9 drops theoretical). In the absence of a laser, a 1 0 dropsmight he necessary for alarge class to heahle tosee the permanent precipitate. Add the remainder of the AgN03, and set the beaker aside. Do the same with the NaCl solution. The theoretical value is
