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V O L U M E 25, NO. 4, A P R I L 1 9 5 3 appendix is of particular value as a representative outline of laboratory exercises for an introductory course in instrumental analysis. Despite the scope of the subject matter, the material in each chapter is detailed in both fundamentals of theory and application. This reflects creditably the ability of each author’s selection of pertinent material for emphasis. Beyond any doubt this book will be welcomed by those chemists with interests in modern in strumentxl analysis. H A M J. STOLTEN
N E W BOOKS Methoden zur Chemischen Analyse von Gummimischungen. Horst E . FrPiI. 104 pages. Springer-Verlag, Reichpietschufer 20, Berlin IT*, 35, Germany, 1953. D N 9.60.
‘ Microscopy for Chemists.
+
Harold F . Schaefler. vi 250 pages 1). Van Sostrand Co., Inc., 250 Fourth dve., Xew York 3, S . I-,1953. $4 50
Volumetric Ana!ysis with the Fisher Titrimeter. 40 pages. Fisher Scientilic C o , 717 Forbes St., Pittsburgh 19, Pa. $2.00.
Statistical Operating Rule for Chemists SIR: I nould like to comment on the paper, “Statistical Operating Rule for Chemists” by LiebhafskJ-, Pfeiffer, and Balis [ A s ~ L . CHEXI.,23, 1531 (1951)]. These authors have made a commendable effort to she\\ hoir chemists might evaluate the quality of analytical results; hut they have given an oversimplified treatment to a problem nhich is, in fact, very coniple\. The following operating rule a a s suggested. -4s a basis of action, it is considered certain that a single determination of an accurate analytical method will give a result within 3s of the true value, where s is the standard deviation established bv the results of a t least 5 replicate determinations according to the method. Eight comments are then given to clarify the rule. The third comment, in effect, restricts the use of the rule to these analytical methods a hich are accurate. I am not sure n hat the authors mean by “accurate,” so I raise the question, “By what criteria should we decide whether or not x e are justified in using the suggested operating rule?” The authois compute s by the formula.
\\here
X L = individual deterniiiialions
Z = average n = number of determination5 and they parenthetically point out that s is an estimate of u, the standard deviation of the universe. They do not explain that the random sampling distribution of s depends upon n; and that ahout 5% of the sample s values will be less than 0.5 u and 5 % will be greater than 1.5 u when n is 5 to 7. This means that
+3s limits based on small groups of determinations will fluctuate, even though the analytical method is well controlled. The authors do point out in their sixth comment that, “The number of replicate determinations done bo establish s is often limited by economics and is governed by the precision to which s must be known. A running adjustment of s is especially desirable in analytical control methods.” But again they do not esplain that the distribution of s is biased so that the average sample standard deviation, 3, is equal to about 0.95 u when the samples contain from 5 to 7 determinations. -4good discussion of the relationship between the sample standard deviation, s, and the universe standard deviation, u, is given by Bowker and Goode (“Sampling Inspection hy Variables.” pp. 106-9, S e w York, McGraw-Hill Book Co.. 1952). The prohlem of making probability statements in connection n-ith the operating rule is discussed in comments 1, 4, 5 , and 7 . The authors conclude, on the basis of the Camp-hleidell inequality, that the proposed operating rule will lead the customer t o make a wrong decision no more often than 1 in 20 times. S o w actually, the customer can make a wrong decision in either of two i m y s . He may conclude, on the basis of the operating rule, that the expected result for a material is not equal to some specifird result, when in fact it really is. The Greek letter cy is universally used to denote the chances of making this kind of wrong decision; and the authors are trying to keep their a risks low \Then they suggest 1 3 s rather than +2s limits. The customer may also conclude, on the hasis of the operating rulr,. that the expected result for :i material is equal t’osome specified result n-hen in fact it reall>- is not. The Greek letter p is used to denote the chances of making this kind of wrong derision. There is a close relationship between these two kinds of mistakes. For a fised number of determinations, we can choose cy as T w please. but p will then be fixed; we can decrease a and p together only by increasing the number of determinations. The authors’ discussion in comment 5 is concerned entirely with cy risks. In actual practice we muet be concerned with both a and /3 risks. I do not see how any simple operating rule can be formulated which n-ill do this. -4good explanation of these so-called producer and consumer risks is given by Dixon and Massey (“Introduction to Statistical .Inalysis,” pp. 206-21, S e w York, McGraw-Hill Book Co., 1951) from the statistical point of view. Bennett (“Quality Control Conference Papers 1952,” pp. 337-42, American Society for Quality Control, Inc., Kew York, 1952) discusses the same problem from the scientific and industrial point of vien*. GRASTWERSIMOST Eastrnan Kodak Co. Rochester, S. Y.
SIR: 11-e elc come Dr. 11-ernimont’s letter because it clarifies certain aspects of our operating rule and gives us a chance for additional comments that are desirable, oving to the terseness of our paper. 1. IT-e gladly admit that the operating rule evolved from the oversimplification of a complex problem. But the oversimplification \vas deliberate, and it seems to us desirable because the operating rule is intended to be applied in situations where a decision must be based on data inadequate for a rigorous statistical treatment. K e hope that these situatione will occur less frequently in the future because we are firm advocates of rigorous statistical methods wherever they can he applied with profit. 2. The operating rule is designed to make more meaningful the 3~ limit,. for a single determination. There is now no agreement as to what these limits ought to be except in the relatively atistical treatment. 1Ve have fe\v cases that permit of rigorou set these limits a t = t 3 s and use them as the basis for a guarantee to the customer. 3. The operating rule states an ideslized case for which the guarantee is estimated to he valid a t least 19 times out of 20. JVe know that actual cases \ d l depart from the idealized. We
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believe that application of the operating rule in most actual cases will prove preferable to guessing a t i limits or to operating witho u t them. The operating rule has no theoretical foundation. 4. We define “accurate method” by the following example. If a sample (either standard or unknown) contains 50% chlorine on the basis of the most recent table of atomic weights, then an analytical method for chlorine is accurate if it yields a chlorine content practically indistinguishable from 50% as the mean of a large number of determinations. According to this definition, accuracy is an operational concept independent of the estimated standard deviation of the analytical method. 5 . We are glad that Dr. Wernimont has pointed out specifically the uncertainties inherent in s, the estimated standard deviation. We consider that a bias of 5% in s may be neglected in guaranteeing the result of a single determination. We recommend that the “running adjustment of s” be made over all the relevant results available so as to reduce, not only such bias, but uncertainties arising from the “random sampling distribution of sJ as well. 6. We agree that the operating rule provides only for a risks, but we do not believe that p risks need be considered if the analytical method is accurate by the definition above. Of course,
actual situations may involve both a and p risks. We agree that no simple rule can be formulated when both risks are present, and we can only fall back on the third sentence under 3 above. 7. Comment 5 of the paper did not make clear that the requirement “if n is very large” applies to the Camp-Meidell inequality as well as to the normal distribution. In both cases, the chances given of falling outside 3s limits are strictly valid when n is large enough to make s and u practically identical. 8. Dr. Wernimont evidently believes, as do we, that blind application of the operating rule is hazardous-in cases, for example, where replication has been unsatisfactory or the sample is not representative. There is unfortunately no substitute for judgment. We have attempted to guard against trouble by making the limits ( & 39) generous, and we repeat that the rule ought not to be applied R hen the data suffice for rigorous statistical treatment. H. A. LIEBH.4FSKY E. W. BALIS
H. G PFEIFFER
‘
Research Laboratory General Electrlc Co. Schenectady, K. I-.
Society of Public Analysts i9th annual general meeting of the Society of Public
Chromatography Past and Present. TREVOR I. WILLIAMS. Far from being a modern discovery, chromatography, with the
LIarch 6, the following officers were elected: president, D. 17‘. Kent-Jones; past presidents serving on council, Lewis Eynon, G. IT. Monier-Williams, J. R. IYicholls, George Taylor; vice presidents, .4. J. Amos, T . lIcLachlan, Eric Voelcker; honorary treasurer, J. H. Hamence; honorary secretary, IC A. \T’illiams: other Adams, S . L. .4llport, h.L. Bacharach, members of council, C. 1. R. C. Chirnside, B. S. Cooper, 11. Corner, D. C. Garratt, S. Heron, H . W. Hodgson, H. 31. IS. H. Irving, H. E. Monk, H. C. S. de Whalley; ex-officio members, T. W. Lovett, chairman of S o r t h of England Section; R. S. Watson, chairman of Scottish Section; A. YI. Waid, chairman of llicrochemistry Group; J. Haslam, chairman of Physical Methods Group; H. 0. J. Collier, chairman of Biological Methods Group. J. R. Sicholls, retiring president, delivered an address on ”Public Health Hazards and the ;Inalptical Chemist.” The ninth annual general meeting of the hlicrochemistry Group was held on January 29 in London. The following officers were elected: chairman, A. M. Ward; vice chairman, G. F. Hodsman; hon. secretary, D. F. Phillips, 101 South Promenade, St. Annes-on-Sea, Lytham St. Annes, Lancs.; and treasurer, G. Ingram. The retiring chairman, Cecil L. Wilson, addressed the meeting on “Microchemistry, an Appraisal.” At the 18th annual general meeting of the Scottish Section held in Glasgow January 28, the following officers were elected: chairman, R. S. T a t s o n , vice chairman, F. J. Elliott; hon. secretary and treasurer, J. A Eggleston, Boot’s Pure Drug Co.. Ltd., h l o t h e r a d St., Airdrie, Lanarkshire. A t a meeting held in Edinburgh April 30 a paper on “Modern Methods of Analysis in the Training of the Student” was presented by Christina C. Miller. At the 28th annual general meeting of the North of England Section held in Manchester on January 31, the following officers were elected: chairman, T. W. Lovett; vice chairman, J . R. Walmsley ; hon. secretary and treasurer, Arnold Lees, 87 Marshside Road, Southport, Lams A. A. D. Comrie gave an address on “Beer Foam.” At a meeting of the society organized by the Physical Methods Group, and held January 30 in Birmingham, the following papers were presented and discussed:
exception of ion exchange chromatography, has been applied in many differentfields of chemistry for at least a century. That it has been widely used only during the past 15 years may he attributed to the fact that only comparatively recently have many problems arisen for which chromatography has unique advantages over older and well established methods. Inorganic paper chromatography was intensively studied by Runge about 1850 and many of his original chromatograms are still extant. In the nineteenth century he was followed by Schoenbein and Goppelsroeder, and in the early twentieth century by Grnss. Modern interest, however, stems from the work of Martin and Synge. The originators of adsorption chromatography were Day, Albrecht and Engler, and Tswett, though as early as 1850 the soil chemists Thompson and Way were perfectly familiar with the separations that occur on columns of adsorbent. Modern interest stems from the application of the method in the carotenoid field initiated by Lederer and Kuhn. Ion exchange chromatography was developed during the last war, when it proved of immense value for isolating the tiny quantities of fission products resulting from the various atomic projects; it also revolutionized the chemistry of the rare earths. There are now few fields of chemical analysis in which chromatography in one of its three principal forms has not proved equal or superior to conventional methods. In the inorganic field an alternative to conventional group analyses has been found in paper chromatography. I n organic analyses it has proved especially valuable in examining complex natural products, such as food and drink, in which unidentifiable constituents often interfere with normal tests. In the biochemical and medical field chromatography has been used in the analysis of such diverse substances as vitamins, hormones, antibiotics drugs, and alkaloids; especially important is the application to urine analysis. The ready availability of radioactive isotopes has proved an important development, particularly i n paper chromatography. Chromatography in the gas phase has proved very valuable in the inert gas field, but undoubtedly much progress can be made here: indeed, this is perhaps the most promising field for future progress.
T THE
A Analysts and Other Analytical Chemists, held in London on
Inorganic Chromatography on Cellulose.
Quantitative Separation D. B. REES-EVANS
of Rhodium, Palladjum, Iridium, and Platinum.
R. 4.WELLS. The separation of the platinum metals has hitherto involved a complicated procedure of precipitation, solution, and reprecipitation. A new method utilizes the principles of partition chromatography in obtaining a quantitative separation of rhodium, iridium, platinum, and palladium. The process, which employs cellulose as the adsorbent and organic solvents as eluting agents, is relatively speedy and is capable of reducing the concentration of one metal in another from 50 t o + O . O O l % , in one operation. When dealing with a mixture of all four metals, a solution of the sodium chloro- salts is freshly prepared in chlorine water and the platinum, palladium, and iridium are AND
