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OF CONTENTS* Reprints of this paper will be available shortly. For details, please see p. 320. t There are included a few later references, and also a few references that ought to have been in the Much literature in this field is "hidden"; we shall be grateful to those who tell us of our earlier review.sins of omission (or other sins).* "Redox buffering" is ordinarily achieved through the H+,H, couple, but sometimes through another system, e.g., uraniumIv, uraniumv'.

Page 2697. In Col. 1, line 6, for "in vivo" read "in vitro."Page 2698. In the second line of formulas, the last one is IV instead of VI.

Titanium in steels and nickel-base alloys can conveniently be determined polarographically after electrolysis of a solution of the alloy in a n~ercur)l-cathode cell. A well-formed wave, the height of which is directly proportional to the concentration of titanium in the solution, is recorded using a supporting electrolyte that is 1.0 111 in tartaric acid, 0.5 AT in sulphuric acid, and 1.2 n/f in ammonium sulphate.The method is one of good precision arid yields values in excellent agreement with those given by umpire methods for samples of basic ope~l-hearth steel, 18-11 chromium-nickel steel, Monel, Inconel "W", and Nimonic 75 and 80. INTRODUCTIONThe only earlier work on the polarographic determination of titanium in metallurgical products appears to be that of Zan'ko, Geller, and Nilcitin (25) who proposed a method for the determination of this element in cast irons and steels. They report the determination of titanium in an acid tartrate medium after treating a solution of the alloy with aluminum dust. We have not been able to remove the interference of iron (111) by the use of this reducing agent; furthermore, the introduction of an appreciable concentration of aluminum ion is undesirable (3).Recent work in this laboratory on the polarographic deternliilation of titanium in rocks and minerals (4) has shown that very good polarographic waves for titanium are obtained in a medium containing tartaric acid, sulphuric acid, and ammonium sulphate. Interfering ions are removed by prior electrolysis of the solution in a mercury-cathode cell. The application of such a method t o the determination of titanium in steels and nickel-base alloys is discussed in the present paper. REMOVAL O F I N T E R F E R E N C E SBecause the half-wave potential for copper (11) in an acid tartrate medium is less negative than that of titanium, there is a limit to the concentration of copper that can be present without the occurrence of interference in the polarographic determination of titanium. Iron (111) also constitutes an interference (23). Electrolysis in a mercury-cathode cell is a very convenient and efficient way of removing from solution iron, copper, and nickel-and a score of other elements (12)-all without the introduction of foreign salts, and often in less time than that required by other procedures. In such an electrolysis chromium is not easily removed quantitatively but the chromium remaining in solution causes no interference in the determination of titanium, even in alloys high (20%) in chromium. The chromium content of the solution being polarographed should be Manuscript received Febrzrary 25, 1952.

This method, however, is subject to interferences (14) from elements that form colored solutions (such as iron, chromium, and nickel), elements that form colored compounds with hydrogen peroxide (such as vanadium, molybdenum, and cerium), and ions that bleach the color of the complex (such as fluoride and large concentrations of alkali salts or phosphate). All these interferences can be overcome

The fascinating hobby de-scribed in this most interesting lecture led to the tracing of the scientific "ancestors" of the members of the staff of the Department of Chemistry at McMaster University.Every scientist has been directly influenced by a number of teachers, and each of these has been influenced by several teachers, and so on back. Thus it is an almost endless and impossible task to elaborate all one's "forebears," instructive and interesting though this would be. In the main, the procedure followed in this work has been to trace the "direct line of descent"; the immediate scientific ancestor of an individual is given as the person under whom the doctorate was obtained, or, in the absence of a doctorate, the person who is believed to have exerted the greatest scientific influence on the individual

mercaptides were precipitated as solids which could be filtered and washed (with 70% alcohol) without centrifuging. Unfortunately, even the low-temperature technique did not permit filtration without centrifuging when applied to primary mercaptans. The accuracy of the modified method for tertiary mercaptans was not established, although the precision was comparable to that of the primar)• mercaptan method. ACCURACY AND PRECISIONA series of straight-chain primary mercaptans containing eight to sixteen carbon atoms per molecule was analyzed. The mercap-tans were prepared from carefully fractionated alkyl bromides which were obtained from alcohols derived from fata. 'The samples were believed to be of the correct molecular weight, but it was suspected that they contained small amounts of nonmercaptan impurities.The results are given in Table I. Each result is the average of at least three determinations.From the results in Table I it is concluded that the method yields the correct molecular weight to an accuracy of 1 to 2 units of molecular weight (0.5 to 1%).Duplicate determinations in general were reproducible to =•=! unit of molecular weight.

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