LUMINESCENCE DVRISG ELECTROLYSIS*
BY NEWTON HARVEY
In a recent paper Dufford’ has referred to the luminescence to be observed at the anode of an aluminium electrode rectifier* and has observed a similar luminescence with eight other metallic anodes and a number of electrolyte ~olutions,~ and also a luminescence with the Grignard compounds in anhydrous ether at anode or cathode with joo to 1500 volts. There are other known cases of luminescence during electrolysis, namely, the light observed by Bancroft‘ when halides are electrolysed a t Hg and other anodes, supposed to be due to combination of halogen and Hg to form the solid halide, and a luminescence a t a metallic cathode when solutions of oxyluciferin and luciferase are subjected to potentials of about I.j volts.5 I n this case the nascent hydrogen appearing a t the cathode reduces the oxyluciferin to luciferin in a layer next. the electrode and the luciferin then reoxidizes in a contiguous layer containing oxygen and luciferase. Luciferin and luciferase are the luminescent substances of luminous animals, light appearing when luciferin oxidizes to oxyluciferin in presence of luciferase. It is suggested that the word galvano-luminescence might be used in referring to luminescences which appear during electrolysis with a galvanic current. Some unpublished experiments of mine carried out a t the Nela Research Laboratory in 1924 indicate an efficiency for this galvano-luminescence of luciferin of I to 5 X IO-’, an order of magnitude comparable t o that given by Dufford and too small to have any practical interest. Such a luminescence can be used as a test for active hydrogen. It appears with Pt or Pd surfaces in contact with hydrogen or when Zn, Mn, -21, and Cd metals are placed in a water solution of oxyluciferin and luciferase. I have recently observed quite a bright luminescence that can be used as a test for active oxygen, formed on anodes during the passage of an electric current and also produced from the decomposition of ozone or H202. This involves the use of a chemiluminescent compound, aminophthalichydrazid, recently described by XlbrechLB When dissolved in alkaline solution (n/ 10 NaOH), this compound gives a brilliant luminescence on oxidation with hypochlorites, ferricyanides, permanganates, persulphates, C1, Br and I,
* Contribution
from the Physiological Laboratory, Princeton University. DuEord: J. Opt. SOC.America, Rev. 5. I., 18, 17 (1929). Lemon: Science, 47, 170 (1918). 3 Dutford, Nightingale and Goddun: J. Am. Chem. SOC., 49, 1858 (1927). ‘Bancroft: J. Phys. Chem., 18, 762 (1914). 6”arvey: J. Gen. Physiol., 5 , 275 (1923); Bull. Nat. Res. Council, Xo. j9 (1927). 6Albrecht: 2. physik. Chem., 136, 321 (1928). The material used in these experiments was kindly supplied by Dr. Alhrecht, to whom I express my sincere thanks.
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and H202, especially if there are present, also substances decomposing H202, including peroxidases and blood. Such an alkaline solution of aminophthalichydrazid will be referred to as hydrazid solution. Luminescence does not appear if pure oxygen is bubbled through the solution but a brilliant luminescence surrounds each bubble of ozone which is passed through the alkaline hydrazid. One should therefore expect to find luminescence a t an anode during electrolysis of hydrazid, free of halogens, and this is fully borne out by experiment. With good stirring of the solution a bright light appears a t 2 . 8 volts and ,0005amperes which will last for some time. If the solution is not stirred a bright flash that dims quickly appears at 2.8 volts and a good steady luminescence a t 0. j volts, undoubtedly due to oxidation of hydrazid by the film of active oxygen. I plan making some efficiency studies a t a later date. Perhaps the most interesting luminescence is that which appears if freshly cut metals such as Al, Zn, Cd, and Sn are placed in the solution of hydrazid in n/Io KaOH. No light was observed with Fe. Ni, Pb, Cu Ag, Cr, Mn, Bi, As, Hg, Au, or Pt. It is especially bright if the metals are lifted out of the hydrazid solution to the air and also especially bright if amalgamated A1 is used, when a continuous stream of H2 is liberated and a precipitate of Al(OH)3 forms. The question a t once arises as to the cause of luminescence, at these metallic surfaces. It is known that hydrogen is formed from water by these metals. One might consider that the energy came from: ( I ) recombination of hydrogen atoms to molecules; ( 2 ) adsorption of hydrazid on metal or on A1(OHj3 surfaces; (3) reaction of hydrazid with Na aluminate, zincate, or stannate; (4) formation of H 2 0 or Hz02 from H2 and dissolved 02. That the first possibility is not the case is shown by the fact that no luminescence appears a t most cathodes (note exception to be described later) where hydrogen is actively freed by electrolysis, and also by the fact that hydrogen in contact with platinized asbestos, or palladinized Pd in Na hypophosphite solutions (which liberates H2), or Mg dissolving in NH4 salts (which also IiberatesHz) shows no luminescence when hydrazid is also present. The second possibility is ruled out by the fact that A1(OH)3,precipitated from AlC13 or XH? alum, mixed with hydrazid solution gives no luminescence,' and the third possibility is also ruled out by the fact that Al, Zn, Cd, and Sn boiled with n,'ro KaOH, the supernatant liquid decanted and mixed with hydrazid gives no luminescence. The zincates, etc , should be formed under these conditions. Regarding the fourth possibility, it is well known since the observation of Traube2 (cf. Burdick3 and Smith4) that H 2 0 2is formed a t moist Zn surA flash of luminescence will occur when hydrazid dissolved in alkali is made acid and also when this acid solution is again made alkaline, so that care must be taken to suspend the Al(0H)a in alkaline solution. Traube: Ber., 26, 1471 (1893). a Burdick: J. Am. Chem. SOC.,48, 1179 (1926). Smith: J. Chem. SOC.,89, 481 (1906).
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faces in contact with air. Dunstan, Jowett and Goulding' obtained the titanic acid test for HZ02 when Zn, Hg, Cu, Pb, Bi, Sn, and Ag (trace) are treated with slightly acid water containing oxygen, but nom with Fe, and Barnes and Shearer2 observed potentials a t A1 and Zn surfaces connected with HZOZformation, but not with Cu, Pt, or Fe surfaces. There is therefore considerable evidence that under certain conditions H202 is formed a t metal surfaces in presence of dissolved oxygen and I believe the hydrazid luminescence a t these surfaces is due to its oxidation by Hz02. HZOZshould also be formed a t cathodes during electrolysis and should be most apparent with those metals possessing the greatest hydrogen overvoltage (since those metals have the least catalytic effect in causing recombination of H atoms, active in HZ02formation). Mercury has a high hydrogen overvoltage and should show luminescence when covered with a layer of aerated hydrazid in n / ~ oNaOH and made a cathode. Such is the cas&. The anode is a point, a fine P t wire, so that the bright luminescence occurring a t the anode will not interfere with observation of the weak luminescence due to HZ02, that actually appears over the cathode Hg surface under these conditions. When the current is reversed and Hg made an anode we can of course obtain the bright luminescence connected with nascent oxygen. Other observations show that luminescence of hydrazid occurs under conditions when we should expect active oxygen to appear. Thus, a piece of phosphorus placed in a layer of hydrazid solution so as to be half covered shows the bluish luminescence of oxidizing hydrazid due to ozone formation a t the P surface, in addition to the greenish luminescence of the P itself undergoing oxidation. H 2 0 2 has been observed in oxyhydrogen and oxy-CO flames3 and i t is interesting to find a beautiful blue luminescence a t the surface of hydrazid solutions when an oxy-gas or air-gas flame is directed on the surface. N o such luminescence is observed a t the surface of water or n/Io NaOH solution. Finally it should be asked why it is not possible to observe oxidation of hydrazid and luminescence a t platinized asbestos surfaces in contact with air or pure oxygen. As a matter of fact no luminescence appears when hydrazid is poured on Pt asbestos4 (several samples were tried) and pure OZ is bubbled through the solution. It is possible that the Pt surface is quickly poisoned by the hydrazid but there is little value in speculation in the absence of experimental data. Dunstan, Jowett and Goulding: J. Chem. Soc., 87, 1548 (1905). *Barnes and Shearer: J. Phys. Chem., 12, 155, 468 (1908). Traube: Ber., 26, 1471 (1893). 4 Sometimes a faint flash of luminescence appears when hydrazid solution is poured on cotton, asbestos fiber, and other finely divided substances.
LUMISESCENCE DURISG ELECTROLYSIS
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Summary Luminescence of aminophthalichydrazid in dilute alkali occurs a t any anode during the passage of current and a t a cathode of Hg, a t moist alkaline Al, Zn, Cd, and Sn metal surfaces, and when oxy-gas flames are played on the surface of the alkaline solution. This luminescence is due to active oxygen. Luminescence of hydrazid also occurs in contact with oxidizing phosphorus and is connected with ozone formation and decomposition. This hydrazid is suggested as a test for active oxygen. A mixture of oxyluciferin and luciferase may be used as a test for active hydrogen. It is suggested that the term galvano-luminescence be used for luminescences associated with the passage of electric current through liquids.
