578 



SCIENCE 



[Vol. LVI, No. 14.55 



rial is placed between the electrodes, the variable 

 effects of intemal and surface changes of the 

 dielectric may be superimposed upon the dis- 

 charge, the result being variable yields. Some of 

 the products of the reactions in the discharge are 

 liable to be absorbed on the walls, the amount ab- 

 sorbed depending upon the condition of the walls. 

 Under certain conditions complete inhibition of 

 the usual reactions results. 



A comparative study of the absorption spectra 

 of phenylasophenol derivatives in the visible re- 

 gion of the spectrum: C. S. Adams, C. E. Booed 

 and Alphetjs W. Smith. This paper is a con- 

 tinuation of the work previously published by 

 Smith and Boord. The present study includes 

 iifty-seven azoderivatives, fourteen of which have 

 not been previously described. Alkali salt causes 

 a displacement of the absorption band toward 

 the red end of the spectrum, the degree of dis- 

 placement varjong with the solvent medium. 

 Substitution causes displacement toward the 

 longer wave lengths, the order for substitution in 

 the phenyl nucleus being, in ascending scale, 

 para raeta ortho and in the phenol nucleus being 

 ortho meta. The nitrophenyl derivatives form an 

 exception to this rule. Weighting of the molecule 

 by substituents follows Nietzki's rule. This is 

 particularly true of the methyl derivatives. For 

 the halogens CI Br I, symmetry of the molecule 

 seems to have a marked effect upon the absorp- 

 tion. Kestoration of the symmetry of azobenzene 

 by substitution of the same group in both para 

 positions produces a marked hypso-ehromic effect. 



The potentials of silver: Silver halide — halide 

 electrodes in light. Part I: S. E. Sheppabd and 

 Felix A. Elliott. Single potentials of an 

 illuminated electrode were measured by the po- 

 tentiometer compensation method, in a cell com- 

 posed according to the system: 



Light 



Ag, AgBr, X KBr aq 



KBraq 



sat. 



Dark 

 X KBr, AgBr : Ag 



0.1 N HBr, Ha, Pt 

 Hence an illuminated electrode could be coupled 

 with an identical unilluminated electrode, or with 

 a standard hydrogen electrode. The following 

 factors in the preparation have to be controlled 

 to secure reproducibility: (1) preparation of the 

 silver surface; (2) halogenizing the electrode; 

 (3) "ripening" the halogenized surface, and 

 aging. With electrodes thus prepared it was 

 found that the potentials, at an iUununation of 

 16 C. M., were reduced as the concentration of 

 bromide was increased, and also by increased 

 bromination in preparing. With constant inten- 



sity of light the electrodes rapidly attained a 

 maximum potential, which then fell off (solariza- 

 tion). Eepeated intermittent exposure and dark- 

 ening, up to 160 minutes, showed no noticeable 

 fatigue. 



Oxidation potentials of permanganates with 

 other manganese compounds: D. J. Brown and 

 S. B. Akonson. 



Energy changes in the reduction of quinones : 

 J. B. CONANT and L. F. Fieseb. The free energy, 

 total energy and latent heat of reduction of a 

 number of derivatives of benzoquinone, naphtho- 

 quinone and anthraquinone have been determined 

 by measuring the oxidation-reduction potential 

 and its temperature coefS.cient. The free and 

 total energy changes are very different for dif- 

 ferent types of quinones. The latent heat of re- 

 duction is approximately the same for all the 

 quinones measured. A method has been developed 

 for measuring the potential in alcoholic solutions 

 and applied to a number of substances too insolu- 

 ble to be measured in aqueous solution. The 

 potential of a given quinone is somewhat greater 

 in alcoholic than in aqueous solution but essen- 

 tially constant in 50, 75 and 95 per cent, alcohol. 

 The potentials in two different solvents are re- 

 lated by an equation involving the solubilities of 

 the oxidized and reduced compounds. 



The effect of substitution on the free energy of 

 reduction. I. Benzoquinone derivatives: yiCTOit 

 K. La Mee and Lillian E. Bakeb. The repro- 

 ducibility and validity of the electro-metric titra- 

 tion method of measuring oxidation-reduction 

 potentials has been established as less than 

 ±0.2 Mv., when precautions are taken or correc- 

 tions made for errors, such as removal of H+ 

 during the reaction, dissolved oxygen, variation in 

 contact potential, etc. (see below). A ground 

 glass stopper makes an excellent junction for 

 titration work, reproducible to ±0.05 Mv. for 

 dilute HCl against saturated KCl. Measure- 

 ments on homologous quinones in acid solutions 

 where the activity ratio quinone hydroquinone is 

 unity show that halogen substitution raises, while 

 alkyl substitution lowers the value of JJo, the 

 normal potential of reduction in the order CI > 

 Br > None > Methj'l > dimethyl ;> methyl, 

 isopropyl > m dimethoxy > phenylene (naptho- 

 quinone). 



Eloctrometric Oxidation — reduction titrations 

 of pure compounds and mixtures: Lillian E. 

 Baker and Victor K. La Mee. Calculation and 

 experiment show that complex formation (quin- 

 hydrone) in the case of nine substituted quinone- 



