Chemical elements. See

Furthermore, isotope analysis is relevant for determining the atomic weight (Ar(E)) of elements. The Ar(E) is the average of all masses of all naturally occurring stable isotopes (taking into account the abundances of isotopes) of a chemical element (see Appendix I10). By consideration of the masses of isotopes (/ ,) and the known relative abundances of all stable isotopes (Xi) with i = 1 to n of a selected chemical element, the average atomic weight (Ar(E)) of this element can be calculated ... 

MELTING POINTS (Chemical Elements . See Chemical Elements. 

Other physical properties of molybdenum are given under Chemical Elements. See also summary of properties of refractory metals under Niobium. 

POLYMORPHISM. 1, A phenomenon in which a substance exhibits different forms. Dimorphic substances appear in two solid forms, whereas trimorphic exist in three, as sulfur., carbon, tin, silver iodide, and calcium carbonate. Polymorphism is usually restricted to the solid state, Polymorphs yield identical solutions and vapors (if vaporizable). The relation between them has been termed physical isomerism. See Allotropes under Chemical Elements, See also Mineralogy,... 

M refers to the table of Radioactive Constants compiled by Meyer, Jakrb. Madiocikt. JUlefdron, 1920, i7 SO I.O. refers to tiie tables given by the International Committee on Chemical Elements, see J. Amer. dhtm, jS oc., 1923, 45, 867 exceptions are indicated hy footnotes. See also this series, Vol. ITT, Paaii I., Table of Constants of the Uraninm-Radinm Series. 

Element 43 technetium (Tc, discovered 1939) 61, promethium (Pm, 1945) 75, rhenium (Re, 1925) 85, astatine (At, 1940) 87, francium (Fr, 1939). Lewis book was quite up-to-date— Hafnium (Hf) was discovered in 1923, the year White Lightning was published, and one can imagine the author happily updating the title of Chapter 72 in the galley proofs. Chapter 86 is titled Niton (now Radon) Chapter 91 is titled Brevium (now Protactinium). For a brief table on the discovery of the chemical elements, see A.J. Ihde, The Development of Modern Chemistry, Harper Row, New York, 1964, pp. 747-749. 

Atomic emission spectroscopy, bom in the mid-19th century, was immediately applied to analyses of minute quantities of chemical elements (see chapter 1). Almost a century later, Alan Walsh (1916-98), Council for Scientific Research in Melbourne, Australia, posed a fundamental question Why were chemical elements anatyzed by emission spectroscopy while... 

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