ANALYTICAL CHEMISTRY
?58 X-RAY DIFFRACTION DATA(determined by J. Whitney and I. Corvin). Cell Dimensions. a = 15.899; b = 5.989; c = 7.995. Formula Weights per Cell. 4. Formula Weight. 167.24. Density. 1.42 (buoyancy; x-ray). Principal Lines
d
I/Il
7.61 6.51 5.57 4.75 4.42 4.26 3.97 3.87 3.78 3.67 3.34 3.21 3.14 2.981 2,815 2.719
1.00 0.40 0.26 0.46 0.39 0.39 0.62 o.fi2
0.97 0.74 0.27 0 70 0.86 Very weak 0.48 Very weak
d 2,579 2,509 2.418 2.398 2.336 2.204 2,172 2.038 1.983 1.942 1.902 1,837 1.769 1.739 1.697 1.667
1/11 Very weak 0.19 0.28 0.26 Very weak 0.20 0.16 0.16 0.24
Very weak 0.26 0.18 0.31 Very weak Very neak Very weak
OPTICALPROPERTIES (determined by 55’. C. %Crone). Refractive Indexes (5893A.: 25” C.). a: = 1.665 * 0.005; 1.667 (1). p = 1.96 += 0.01: 1.965 (1). y = 2.04 (calcd.): 2.06 (1). CY’ (projection on 001) = 1.688. (This refractive index
Polarograms by an “Undamped” Polarograph SIR: In a recent paper by Lingane (1) the following statement is made concerning the 25% sensitivity increase obtained by Schulman, Battey, and Jelatis m-ith “undamped” operation over that obtained by conventional damped operation of their new polarograph ( 2 ): “The alleged increase in sensitivity that results from measurement of the maximum rather than the average of the undamped recorder oscillations is more or less illusory, because the residual current in terms of maximum oscillation is also larger.” Lingane’s statement implles that the sensitivity is determined by the ratios
-or __ which do not change with change
I d i f fusion Iresidual
Iresidual’
in damping. Xeither these ratios nor the residual current are involved, however, in the expression for the sensitivity. This quantity is defined as K in the equation: I d , f f u s l o n = KC, where I d , f f L s i o n is the diffusion current and C is the concentration of electro-oxidizable or electroreducible substance. “Cndamped” operation increases both the residual current and the total current by 25%. Therefore their difference-the diffusion currentis likewise increased by %%, and sensitivity K is increased by this amount. The data of Schulman, Battey, and Jelatis unequivocally demonstrate the reality of this increase in sensitivity. It is granted that a sensitivity gain of 50 or 100%-had this been obtainable by changing from damped to undamped operation-would be of greater practical value than the observed 25% gain. I t appears to the writer that a sensitivity increase of this magnitude is nevertheless worth has6ng. Lingane has correctly stated that the principal advantage of the undamped instrument lies in the speed with which polarograms can be run m ithout distortion of half-wave potentials. LITERATURE CITED
(1) Lingane, J. J., AIEAL. CHEM.,21, 45 (1949)
is not correct, but is the Cargille liquid which, when s a k a t e d with mercaptobenzothiazole, causes the crystal to disappear.) Optic .$xial Angles (5893 A.; 25’ C.). 2 T’ = 52‘; 50’ (1). 2H = 70 ; 67” (1). Dispersion. Inclined T > 1’. (Sote. Conoscopic observation parallel to B X a shows both brushes in the field with K.A. = 1.25; one optic axis shows v > T , and the other, T > L,.) Sign of Double Refraction. Kegative. a:. .icute Bisectri:. Extinction. j la. Molecular Refraction ( R ) (5893 8.;25” C,), 4 37 = 1.881. R (calcd.) = 49.4. R (obsd.) = 53.9. FTXIOS DATA(determined by W.C. JIcCrone). 2-Nercaptobenzothiazole melts at 181O C. and solidifies spontaneously on cooling. There is a slight tendency for sublimation but usually only droplets or long needles (elongated parallel to b ) are obtained. The crystals g r o x rapidly from a small number of nuclei as spherites made up of large rods and needles groiving elongated parallel to b. Thcse cryst,als shom all possible orientations normal to the b axis. Some views using oil immersion show both optic ares vithin the firld with 2H = 70”. The interference figure is unusual in that one optic axis shows strong dispersion, r > z’, and the other shows less dispersion, > r. The sign of double refraction is negative. LITERATURE CITED
(1)
RIitchell, ASAL. CHEM.,21, 448 (1949).
(2) Schulman, J. H.. Battey, H. B., and Jelatis, D. C., Rev. S e i . Instruments, 18, 226 (1947).
JAMES H.
SCHL-LX1.4X
Naval Research Laboratory Washington, D. C.
SIR: Schulman is correct in his criticism of the reason which I stated for my opinion that the increased sensitivity Fyhich results from measurement of undamped maximum polarographic recorder oscillations is more or less illusory-viz., “because the residual current in terms of maximum oscillations is also larger.” I am glad to accept correction on this point. The thought in mind, which I did not express correctly, is that increasing the magnitude of a measured quantity by only 25% does not produce any very significant increase in the sensitivity or precision of the measurement. JAMES J . LISGASE Harvard University Cambridge, Mass.
Polarographic Method for Copper, - - _ lead, and Iron SIR: We have read with great interest the paper entitled “Polarographic Method for Copper, Lead, and Iron” [ANAL. CHEaf., 21, 176 (1949)l by Reynolds and Rogers. However, we feel that two topics of considerable importance have been unduly slighted in their discussion: 1. Directions are given for the preparation of the solution for analysis, but the optimum pH is not stated. This matter is likely to be of vital interest to a user of the method. 2. The reported effect of gelatin on the lead wave is strikingly similar to the effects we have found with a number of micelleforming agents in other systems. From a study of the effects of gelatin on several copper tartrate systems, we have concluded that the critical concentration for micelle formation of gelatin is
759
V O L U M E 21, NO. 6, J U N E 1949 close to 3.5 x 10-3 yo. It would be of interest to know whether the region in which the effect was found by Reynolds and Rogers is in agreement with our data.
metric methods for the analysis of metallurgical specimens, this section may be a disappointment until it is recalled that the title of the book is “Absorption Spectrophotometry,” a physical phenomenon for which the analytical chemist finds useful applicaLOUISMEITES EUQENE L. COLICHMAN tion in various ways. I n the section on techniques (77 pages) the Sterling Chemistry Laboratory author describes in some detail the instrumentation available for Yale University visual, photographic, photoelectric, and thermal spectrophoNew Haven, Conn. tometry, with most emphasis on those particular instruments with which he has had personal experience. The worker whose equipSIR: The optimum pH for the analysis was found to be between ment is not described may feel some disappointment, but as the 9 and 11. Below pH 9, zinc pyrophosphate begins to precipiauthor points out, instrumentation is developing so rapidly that tate; above pH 11, the various hydrous oxides begin to precipino treatment of the subject can long remain up to date. tate. The author lists 219 literature references in the text, and sugIt was found that O.Ol~ogelatin was not sufficient to suppress gests 21 other books and papers as valuable sources of additional the copper maximurn completely, but that it depressed the lead information on spectrophotometry. wave to about 10% of its true height. Therefore, higher conPAULK. WISTER centrations of gelatin were not tried. The copper maximum was not sufficiently suppressed by 0.001% gelatin to permit the Elastomers and Plastomers. Their Chemistry, Physics, and determination of the lead diffusion current, owing to overlapping Technology. Volume 111. Testing and Analysis: Tabulation of the two wives. By using pyrophosphate solutions containing of Properties. R. Houwink, editor. 174 pages. Elsevier only lead a t pH 10, it was found that 0.001% gelatin was not Publishing Co., Inc., 215 Fourth I v e . , New York, iX.Y. Price, enough to depress the wave height appreciably. Concentrations $4.50. of gelatin intermediate between 0.001 and 0.01% were tried in copper-lead mixtures, but either the overlapping was too great This volume is a compilation of physical, chemical, mechanical, or the lead diffusion current was cut down too much. X o optical, and electrical test methods for many applications of the quantitative studies ivere made to correlate the decrease in the plastics using the principal types of resins. Typical values oblead diffusion current with the gelatin concentration, but even tained by these methods are tabulated in two chapters, subdivided these data are in good qualitative agreement with the results into elastomers and plastomers. American, British, and German on other systems reported by Meites and Colichman. standard methods, as well as isolated examples from other CH.4RLEs -4.REYNOLDS countries, are incorporated in obtaining these data. Xethods of Department of Chemistry determining the presence of typical classifications of resins are inThe University of Kansas cluded. KOtest methods or results on the behavior of resins in Lawrence, Kan. solution have been included-e.g., solution viscosit,y. This book should serve as a reference on plastics for the over-all comparison of test methods and values obtained therefrom. R. C. Bacozr
Industrial Uses of Radioactive Materials Absorption Spectrophotometry. G. F . Lothian. 196 pages. 76 illusri,ations and diagrams. Hilger and K a t t s , Ltd., 98 St. Pancras Way, Camden Road, London, K.W. 1, England, 1949. Jarrell-.hh Company, 165 Sexbury St., Boston, Mass. Price, $7.60, postage prepaid. This book wa9 originally intended to be a third revised edition of Twyman and .Ilsopp’s “The Practice of Absorption Spectrophotometry with Hilger Instruments,” but the tremendous adyances in this field since the appearance of the second edition of t h a t book in 1934 makes the present edition virtually a new work. With each opening of the book, the reviewer’s respect for it has ncreased, and he is now convinced that the author has made a worthy contribution by condensing so clearly and concisely in less than 200 pages the essentials of the principles and practice of absorption spectrophotometry. This volume might well perform the dual role of orienting the nen-comer in the field and serving as a valuable handbook to the experienced worker. The subject matter is well organized and treated in three parts: principles, applications, and techniques. The discussion of theoretical principles is sound and is about as complete as one could expect in 62 pages. One might take exception to some of the terminology employecl-e.g., density instead of the somewhat more specific expression optical density, or better still absorbancy-but on the whole there is nothing that should cause any confusion. Obviously the practical applications can only be indicated in the 35 pages allotted to this subject, especially in vie;v of the wide spectral range covered, roughly 2000 to 250,000A. ( 2 5 ~ ) . To one whose principal interest is in, say, spectrophoto-
A selected bibliography on industrial uses of radioactive materials has been prepared by Arthur D. Little, Inc., Cambridge, Mass., as an 18-page pamphlet. Following a 2-page introduction, six general background references are cited. Survey articles of industrial applications are then listed and the bibliography continues with references dealing with specific fields: petroleum industry, mining and metallurgy, textiles, instruments, radiography, analysis, pharmaceutical, glass, radioisotope preparation, and miscellaneous industrial applications. Copies of the bibliography are available on request from Arthur D. Little, Inc., Nemoriai Drive, Cambridge 42, Mass.
American Council of Commerical Laborstories. Curtis Hotel, Minneapolis, Minn., June 23 and 21 American Society for X-Ray and Electron Diffraction. Cornel1 University, Ithaca, K. Y . , June 23 to 25 Second Annual Summer Symposium on Analytical Chemistry. Wesleyan University, Middletown, Conn., June 24 and 25 Fourth Instrument Conference and Exhib:t. Municipal Auditorium, St. Louis, Mo., September 12 to 16 Third Symposium on Analytical Chemistry. Louisiana State University, Baton Rouge, La., January 30 to February 2, 1950
