V O L U M E 2 4 , N O . 12, D E C E M B E R 1 9 5 2 lcI.v:-li(”
-Ij‘
..”.,\
-:
2009
-,
Research and Development during World War 11. Alfred T. Blomquist was technical representative of OSRD Section B-!-A supervising progress of this work. Sien-Moo Tsang and John H. Andreen were also associated with this project and contributed to the above description. CONTR~BUTIONB of crystallographic data f o r this seotmn should be sent to Walter C. MoCrone, Analytical Section, Armour Research Foundation of Illinois Institute of Technology,Chicago 16,Ill.
Figure 1. Crystals of 4,6-DinitroresoreinoI by S u b l i m a t i o n
Reliability of Photoelectric Photometry SIR: I n the article “Reliability of Photoelectric Photometry” [Gridgeman, N. T., ANAL.CHEM.,24, 445 (1952)l reference is made to an equation presented by Stearns (Stearns, E. I., “Analytical Absorption Spectroscopy,” M. G. Mellon, ed., page 338, equation 7.11, New York, John Wiley & Sons, 1950) with the implication that the equation involves the statistically abhorrent simple addition of errors. This implication is incorrect. In Gridgeman’s article, the Martens photometer is not treated a t all; the article deals only with the situation in which the error in reading the transmittance is considered t o be constant over the entire transmittance scale. The familiar form of the error equation is
c
Gridgeman points out that if the error in setting the 100% line, considered t o be equal in magnitude to the error in the test reading, is taken into consideration, the equation becomes
re 2.
Orthographic Projection of Typical Crystal of 4,6-Dinitroreso,reinol
cD/D ~=~ OT
of 4,6-dinitroresoreinoI grow into thymol elongated D. The terminal angles itre all about 147‘. Iuterres between Bz. and the optic itxis are obtained. I
TInT
He also points out that if the errors of test reading and 100% line reading are not added under the radical, the iollowing abhorrent equation results,
ACKNOWLEDGMENT
the work described above was performed under a tween Cornell University and the Office of Scientific
(3) By the purest coincidence, this equation is practically identical in form with equation 7.11, which is CAS - T.log T8 -AC 1 T.
+
Figure 3.
4,6-DinitroresoreinoI f r o m Fusion
14) -, I
since ooncentration is proportional to absorbance. Gridgeman correctly implies that log should be written In in Equation 4. However, the two equations deal with two entirely different optical arrangements. Equation 4 corresponds to Equation 1, but deals with the specific ease of the Martens photometer which is governed by the laws of polarizing prisms. The (1+T,) factor in Equation 4 arises from a series of cancellations of trigonometric functions and not from any statistical reasoning, f d t y or otherwise. Incidentally, while the precision of setting the 100% line i s of importanoe in the type of instrument discussed by Gridgeman, i t is of no importance in the method of interpreting spectrophatometric curves recommended by Shurcliff and Stearns [J.Opt.
ANALYTICAL CHEMISTRY
2010 SOC.Amer., 39, 72 (1949)l. The reference point is obtained by the use of a calibrated gray filter having a transmittance approximately equal to that of the sample.
method is considered to be a special case of the more grinera1 treatment offered. LITERATURE CITED
Calco Chemical Division, American Cyanamid Co., Bound Brook, N. J.
EUGESEA 4 L L E N
E;. I. STEARXS
SIR: The odd coincidence of the two equations, one statistically weak, the other optically correct, confused me and I see that my censure was misplaced. The assumed misprint was that “log” meant “loglo” and should have been printed “loge” or “In.” At the time I x a s encountering w o n g equations, in particular 1) additive-error one, often in the literature. I saw the ( T that this equittion specifically referred to the Martens-Rochon setup (n-ith xhich I am not familiar), but could not follow the derivation. I now understand that equation 7.11 is thP couriterpart of the Twyman-Lothian equation in the sprcial circumstance of rotating-prism instruments. I think I should have better understood 7.11 I f 7.9 had been witten
+
AL = sin2A - ( T ,
+ A T , ) cos2*4
for that is the real but hidden key to the derivation. I agree with the last paragraph of the letter from Allen and Steams; it ties up with the general advantageousness of comparative work with transmittancy differences minimized. Division of Applied Biology, Xational Research Council, Ottawa 2, Canada
Dead-Stop End Point SIR: The recent article of Stone and Scholten ( f f ) concerning the “dead-stop” end point advances a very logical and tenable explanation of the phenomena occurring a t the indicator electrodes. Homver, they failed to cite a number of articles dealing with the same types of electrode systems and offering similar explanations of the phenomena observed. Attention is called to the article of Myers and Sn-ift ( 7 ) in Fhich the end point of a coulometric titration was observed by use of a pair of platinum indicator electrodes inserted in the titration mixture. Their experimental procedure involved a refinement of the dead-stop technique in that the end point was determined by extrapolation of Etraight lines rather than by a change in the magnitude of the indicator current. Myers and Sn-ift were able to relate the magnitude of the indicator current to the concentrations of substances present through Fick’s laws of diffusion, as had been done previously by others ( 4 , 6) for somewhat similar situations. The fact that the reagent was produced by electrolytic generation mith a second pair of electrodes rather than added from a buret as in Stone and Scholten’s work does not alter the mechanism of the indicator electrode system. Furthermore, the latter’s plot of the current us. volume for a complete titration is similar to that of Wooster, Farrington, and Swift ( f z ) , which should have been noted. A number of examples have appeared in whirh the end point of a titration is determined by a pair of identical electrodes, one of which becomes unpolarized a t the end point. Among the redox couples that have been used successfully in this manner are: the iodine-iodide system ( 8 ) , the bromine-bromide system (1, 2, fO), the chlorine-chloride system (S), and the cupric-cuprous system in chloride media (6). Reilley, Coolre, and Furman (9) have explained the dead-stop end point in terms of a three-dimensional model relating polarography, amperometry, potentiomd r y , and polarized end-point phenomena. The dead-stop
Brown, R. A., and Swift, E. H., J . Am. Cheni. Sac., 71, 2717 (1949). Carson, W.N., Jr., ANAL.CHEM.,22, 1565 (1950). Farrington, P. S., and Swift, E. H., Ibid.,22, 889 (1950). Kolthoff, I. AT., and Lingane, J. J., ”Polarography,” p. 435, Interscience Publishers, New York, 1946. Laitinen, H. A , and Kolthoff, I. AT., J . Phys. Chem., 45, 1079 (1941). hfeier, D. J., hfyers, R. .I., and Swift, E. H., J . S m . Chcm. SOC., 71, 2340 (1949). Myers, R. A., and Swift, E. H., Ibid.. 70, 1047 (1948). Ramsey, W. J., Farrington, P. S.. and Swift, E. H., -1.v.~~. CHEM.,22, 332 (1950). Reilley, C. N., Cooke, IT, D., and Furman, N.H., Ibid.,23, 1226 (1951). Sease, J. W,, Niemann, C., and Swift, E. IT., Ibid., 19, 197 (1947). Stone, K. G., and Scholten, H. G., Ibid., 24, 671 (1952). Wooster, W. S., Farrington, P. S., and Swift, E. H., Ibid., 21, 1457 (1949).
ROBERT 1,. PECSOK University of California, Los Angeles, Calif.
ASTM Committee D -2 on Petroleum Products and lubricants HREE important publications of the American Society for l.Testing 3Iaterials Committee D-2 are nearing completion: “ASTM ’Standards on Petroleum Products and Lubricants”; a revised and considerably extended edition of “JIanual of Engine Test Methods for Rating Fuels,” and s new book--“ASTlI-IP Petroleum Measurement Tables.” Technical Committee A on Gasoline (H. 31. Smith, chairman) has revised ASTbl D 439, specifications for gasoline (tenhtive). Research method octane number (ASTM D 908) has been adopted to replace the motor method octane number (ASTLI D 357). On the basis of the winter 1951-52 Bureau of Mines survey research octane numbers of 78 minimum for regular and 85 minimum for premium-price gasolines have been selected. The committee has been reorganized to include: Section I. Specifications, J. 11. Campbell, chairman Section 11. Volatility, R. C. Alden, chairman Section 111. Gum and varnish, S.S. Kurte, Jr., chairman Section IV. Sulfur and corrosion, P. C. Khite, chairman Section T’. Antiknock value, F. C. Burk, chairman Section VI. Tetraethyllead, C. 11,Gambrill, chairman Section VII. Storage stability, IT. R. Power, chairman Section VI1 has prepared a report showing correlat,ion of data on storage stability of gasolines with data on gasolines tested by ASTM D 525. Technical Committee B on Lubricating Oils (W. S. James, chairman) has active work under way in Section U-I11 on industrial gear oils (C. L. Pope, chairman). Section U-V on instrument oils (E. H. Erck, chairman) is investigating performance, spreading, corrosion, and oxidation characteristics of instrument oils. A Special Subcommittee on Railxyay Car Journal Lubrication was formed (J. J . Laudig, chairman). Section I on Oiling Systems (F. E. Rosenstiehl, chairman) of Technical Committee C on Turbine Oils (F. C. Linn, chairman) plans to study rusting of turbine oil systems in service. The section also a& as a joint ASME-ASTM Committee on Turbine Lubrication, and is continuing studies preparatory to issuing “Recommended Practices on Design of Turbine Lubricating Systems” and “Preparation of Turbine Lubricating Systems for Lavup.” ASTM D 665, test for rust-preventing characteristics of steamturbine oil in the presence of water (tentative), was revised.
