1071
V O L U M E 2 4 , NO. 6, J U N E 1 9 5 2 Formula %-eights per Cell. 4 (4.00 calculated from x-ray data). Formula Weight. 298.32. Density. 1.2565 (flotation, centrifugation, and density balance); 1.256 (x-ray). Principal Lines d 9.3 6. 1 5.22 5.16 4.45 4 18 3.95 3.74 3.69 3.43
d 3.19 3.05 3.00 2.94 2.76 2.65 2.55 2.47 2.43 2.27
1/11 0.30 0.10 0.10 0.45 0.47 0.28 0.01 1.00 0.03 0.07
I/Il 0.38 0.02 0.02 0.06 0.04 0.06 0.02 0.04 0.04 0.04
OPTICALPROPERTIES.
Refractive Indices (5893 *i.;25' C . ) = 1.519 & 0.002. 8 = 1.628 i 0.002. y = 1.645 i 0.002. Optic .bial Angles (5893 A.; 25" (3.). 2 E = 73'. 2V = 42.5' (calculated from p and 2 E ) ; 2V = 41" (calculated from a. 6,and y). Diqpersion. v > T , very weak. Optic .%yialPlane. 001. (Y
Sign of Double Refraction. Segative. hcute Bisectrix. 01 = b. Extinction. Parallel and symnietrical. Molecular Refraction ( R ) (5893 A.; 25" C,). .\"/ocs, = 1.59ti. K (calcd.) = 81.4; R (obsd.) = 80.8. FUSION D a ~ a . Dibenzylsuccinate melts a t 46" c. with veiv little decomposition. When recrystallized from the melt, on a microscope slide, this compound crystallizes as birefringent rods or plates (Figure 3). The direction of growth is parallel to c and, in general, these crystals show a centered or slightly off-center BxO figure. Dibenzylsuccinate supercools readily after fusion and considerable shock is required to initiate crystallization. S o polymorphs were observed in this study. ACKNOWLEDG.\IEYT
The author gratefully acknowledges the assistance oi Dorothy Baranski, who took the photomicrographs, and of Irene Corvin and Joan French, n-ho determined the powder x-ray spacings and intensities. CONTRIBUTIOTS of crystallographic data for this section s h o d i b e sent to TTalter C. RZcCrone, Analytical Section, h r m o u r Research Fcindation of Illinois Institute of Technology, Chicago 16. Ill.
Exaltation of the limiting Current of Oxygen by Hydrogen Peroxide at the Rotated Gold Electrode as a Means for Amperometric Determination of Traces of Oxygen a preliniinary publication ( 2 ) it was shown that hydrogen IatSedperoxide increases the limiting current of oxygen at the roplatinum electrode. The following interpretation of this
t
exaltation mas given. It IS assumed that the electroreduction of oxygen to hydrogen peroxide norinally occurs in two steps:
O2
+ e --+02-
T f I i ~ - d r i > g (iwroxide ~n is acldctl t o the solution, it reacts with t8he i i i i rrmrtiiat
el y foniietl 0,-:
+ H202 +OH- + 02 + OH OH + e--+OH-
(3) (4) Reaction 3 apparently is faster than the reduction of Os!Equation 2). Hence 0 2 is regenerated continuously, thus account,ing for the exalbation. The over-all result' is that the electroreduction of oxygen induces the reduction of hydrogen peroside at the rotat,ed platinum electrode. 0 2 -
In subsequent work it was found that in buffered solutions of pH 4 to 13 the hydrogen overvoltage a t a rotated gold wire electrode is about 0.4 volt, while at' the rotated platinum electrode it is negligible. Consequently, the diffusion current of oxygen, and also its limiting current exalted by hydrogen peroxide, exwnd over a wider range of potentials a t gold than a t platinum. Hence a rotated gold wire electrode should be preferable to platinum as indicator electrode for the voltammetric determination of oxygen. Experimentally this n-as found to be true. We used an annealed gold wire 0.3 mm. in diameter and 6 nim. in length, synchronously rotated a t 600 r.p.m. Oxygen m-as determined by measuring its diffusion current in the concentration range between 5 X and 2.6 X J1,corresponding to partial pressures of 4 X 10-3 to 2 X lo-' atm., x i t h a precision and accuracy of f 2 % , i d ; c being equal to (221 rt 4) pa. per millimole per liter a t 25O.
The exaltation by hydrogen peroxide was used in deteriiiiniiig concentrations less than 5 X -11 of oxygen. The coiiceiit.ration of the peroxide should not exreed 10-3 -11,because at higher concentrations the peroxide yields a current-voitage curve which interferes with the oxygen wave. The exaltation of the limiting current was found proportional to both the oxygen and hydrogen peroside concentrations when the molar concentratioii of the peroxide was a t least 200 times greater than that of the oxygen. Quantitatively the "exaltation" is defined as the ratio between the limiting current in the presence of hydrogen peloxide, il, and the normal diffusion current of oxygen, i d o , , In ,If hydrogen peroxide &/ido2 v a s with our electrode equal to 90 in buffer solutions of pH between 4 and 9, to 69 in 0.1 21 sodium hydroxide, and to 30 in 1 JI sodiuni hydroxide. Many analytical applications of the exaltation are self-evideilt. B s an example, the following procedure was used for Lhe determination of t.races of oxygen in coinniercial inert gases. The instrumental setup and the purification of t'he nitrogeu used for deaeration w?re the same as described in a previous paper ( 1 ) .
Use a gold electrode approximately 0.3 mm. in diameter and 6 mm. in length. Soldei. t o a copper wire, seal into a glass tube, and est,ablish electrical contact, to the copper with the help of mercury. Wash the electrode in 10 -11' nitric acid and rinse ITith water. Prepare a supporting electrolyte solution, such as 0.1 .If sodium hydroxide, 0.05 31 boras, a phosphate buffer of pH 7 , or an acetate buffer of pH 4. Introduce a fritted-glass disk bubbler (5) into the o en electrolysis cell, place in a therniostat a t 25', bubble the unffnown gas through a measured volume of the supporting electrolyte, immerse the electrode, and electrolyze for 10 minutes a t - 2 volt,s (m. S.C.E.). Continue bubbling until distribution equilibrium is reached. Stop bubbling and let the gas pass over the surface of the solution. Inject oxygenfree hydrogen peroxide mith a calibrated syringe t o make the in peroxide. Measure the limiting current, solution 0,00100 ~$1 iz, a t a pot.entia1 of -0.8 volt us. S.C.E. Correct for the residual current obtained with an oxygen-free blank. To comput,e the oxygen content of the sample determine a t 25p C. the diffusion current of the air-sat'urated sup rting electrolyte in the absence of hydrogen peroxide and use tK exaltation values given above for &'hydrogen peroxide solutions.
1072
ANALYTICAL CHEMISTRY
Let if be the diffusion current of oxygen in the air-saturated supporting electrolyte, iz the exalted limiting current, and E the exaltation. Assuming that air contains 20.7% oxygen, the oxygen content, X, of the sample, is given by the relation
x=-E X iF i1
X 20.7 volume
%
As an illustration, the following data were obtained in the determination of oxygen in high purity tank nitrogen, using a phosphate buffer of pH 7 (E = 90) as supporting electrolyte: iyt = 58pa.; iz
= 5pa.;
X
= 0.020 vol.
%
Applying the exaltation procedure a t our electrode, oxygen u-as determined in a concentration range between 10-7 and 5 X 10-6 M, corresponding to partial pressures of 8 X 10-6 to 4 X 10-8atm. a t 25”, with a precision and accuracy of %4% or better. By working with larger gold electrodes, the method can probably be applied with the same precision to smaller concentrations of oxygen. It is recommended that the value of E be determined
A Text-Book of Quantitative Inorganic Analysis. A . I . Vogel. 2nd ed. xxiii 918 pages. Longmans, Green and Co., 55 Fifth Bve., Xew York 3, N. Y., 1952. Price, $10.
+
experimentally for electrodes of size considerably different from that used in this investigation, Substances that decompose hydrogen peroxide interfere. For this reason it is essential that high purity chemical3 and water (free of copper) be used in the preparation of the supporting electrolytes. Acknowledgment is made to the Research Corp. for a grant in support of this work. LITERATURE CITED
(1) Kolthoff, I. hl., and Jordan, J.. J . Am. Chem. SOC., 74, 382 (1952). (2) I b i d . , p. 570. (3) Laitinen, H. A,, and Burdett, L. W , , A X I L CHEM..22, 833 (1950). SCHOOL OF CHEMISTRY UNIVERSITY OF MIXNEAPOLIS 14, M I B N . MINNEAPOLIS RECEIVED April 18, 1952. Accepted May 9,1952.
I. 11. KOLTHOFF JOSEPH JORD~N
new and improved photomicrographs are included. The public&tion may be divided into three sections: text, tables, and photomicrographs. The text describes fiber characteristics a t some length and includes also several specialized tests and procedures for examination and staining. The tables allow for running down an unknown fiber either with or without the use of a microscope. A series of 64 photomicrographs depicts most of the natural and synthetic fibers in longitudinal view and cross section. Conspicuous by its absence in almost all fiber identification schemes, the present included, is the use of specific refractive indices, birefringence, and sign of elongation-optical data of considerable value in identifying synthetic fibers, especially. The need of a polarizing microscope for these determinations does not justify their total neglect. Nevertheless, the committee is to be commended on a thorough job of producing a very excellent determinative manual as up to date as is possible in the face of the present-day activity in synthetic organic fibers. The authors rightly emphasize microscopical methods as the most satisfactory means of identification, and caution that experience and skill are required for the correct interpretation of the microscopical image. The British appear to have done a more comprehensive and up-to-date job than either the A.S.T.M. D 27649 or the ;I..LT.C.C. Tentative Method 20-47. These reviewers heartily recommend the manual to everyone interested in fiber identification.
This edition is more than just a textbook for students at the college level. The author describes it well in the preface, when he states that one of his main aims is to provide information of value “to practising analytical chemists and t o all those workers who have occasion to utilize methods of quantitative inorganic analysis.” Approximately two thirds of the 918 pages of this textbook are devoted to gravimetric and volumetric analysis, one fourth to spectrophotometry and electroanalytical methods, and the remainder to gas analysis and microanalysis. The theoretical treatment of all these subjects is excellent. As may be expected from the size of this text, there are numerous determinations which serve a dual purpose in demonstrating theory and in aiding those who utilize methods of analysis. The large amount of material may limit the adoption of this textbook to courses which have a duration of more than one semester. The absence of problem sections, although there are some examples of numerical solutions, may also necessitate the use of companion textbooks which are devoted to the calculations of analytical chemistry. The author has carefully considered the question of literature references and omits them in favor of selected bibliographies. However, the reviewer believes that G. E. COVEN the inclusion of these references is necessary for those analytical T. G. ROCHOW chemists and other workers mentioned above. The organization, the range of material, the graphic illustrations, and the writing style of this textbook are admirable. It Experimental Nucleonics. Ernst Bleuler and G. J. Goldsmith. will make a worthy addition to the library of anyone engaged in xv 393 Daees. Rinehart & Co., Inc., 232 Madison iive., the study and practice of analytical chemistry. York 16, N: 3?, $6.50. LOUISGORDOX Measurement at Centimeter Wavelength. D. D. King. 334 nanes. D. Van Sostrand Co.. 250 Fourth Bve.. Yew York 10, ‘\;.“Y. $5.50. 1951 Supplement to Book of ASTM Standards Including TentaIdentification of Textile Materials. 3rd ed. 94 pages. The tives. American Society for Testing Materials, 1916 Race Textile Institute, 10 Blackfriars St., Manchester 3, England, 401 St., Philadelphia 3, Pa. Part 1, Ferrous Metals. xi 1951. Price, 10s. 6d. pages. $3.50. Part 2, Kon-Ferrous Metals. xi 343 pages. $3.50. Part 3, Cement, Concrete, Ceramics, Thermal Insula265 pages. tion, Road Materials, Waterproofing, Soils. xiii Prepared by General Technical Committee C, a subcommittee $3.50. Part 4,Paint, Naval Stores, Wood, Adhesives, Paper, of the Unification of Testing Methods Committee, this edition Shipping Containers. xiii 249 pages. $3.50. Part 5 , Texhas been very cohsiderably expanded and modernized since the tiles, Soap, Fuels, Petroleum, Aromatic Hydrocarbons, Antisecond edition, published in 1948 as Tentative Textile Specifi324 pages. $3.50. Part 6, Electrical freezes, Water. xii cation No. 13. The analytical tables have been reorganized and 233 pages. $3 50. Insulation, Plastics, Rubber. xiii
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