SOME RECENT ADVANCES IN The first quarter of the twentieth century has seen a remarkable advance in every branch of chemical science. Not only has increased knowledge been acquired by research along familiar lines, but new fields. have been opened up by the aid of fresh implements with the result that many new fundamental conceptions have arisen and some old ideas have been discarded. Most of these greater discoveries have occurred on the borderland of physics and chemistry, and are concerned with X-ray spectra, atomic numbers, isotopes, electrons, atomic structure and radioactivity. All these and many other subjects are discussed in the new edition of Prof. A. W. Stewart's "Recent Advances in Physical and Inorganic Chemistry."* The rapidity with which discoveries are being made may be inferred from the alterations made in this book compared with the fourth edition, which appeared as late as 1922. The author has written a dozen new chapters, and only three of those of the last edition remain intact. As might be expected, much space has been devoted to researches which have increased our knowledge of the atom. The old notion that the atom was the unit engaged in chemical change has been disproved and the complex structure of the atoms of even the lighter elements has been established. By studying the passage of an electric. current through evacuated tubes, Crookes *Recent Advances in Physical and In Organic Chemistry. By A. W. wave paved the way for the discovery of cathode rays, positive rays, and X-rays, all of which characteristics that possess important have been turned to good account in scientific work. When cathode rays impinge upon a metal surface, this emits characteristic X-rays of definite lengths, which can be photographed and measured. In this way Moseley discovered that the X-ray spectra of all the elements showed а definite regularity, enabling elements to be identified with certainty. By assigning (from calculations) each element an atomic number, in ascending order, according to the wave-lengths of the K lines, it has been possible to correct the old anomalies of the periodic Classification. Thus argon and potassium, and iodine and tellurium fall into their proper groups, having the atomic numbers Ar, 18; K, 19; I, 53; and Te, 52. The atomic number of uranium has been found to be 92. Assuming this to be the element of highest atomic number, there still remain a few elements to be discovered. Until 1923 these included the element of atomic number 72 but in that year Coster and Hevesy announced its discovery by means of X-ray analysis in zircon minerals. Since Prof. Stewart's book appeared, the number of missing elements has been further reduced. In the last few weeks it has been announced that Prof. B. Smith Hopkins has discovered the missing rareearth metal of atomic number 61, and during last year dvi-manganese of atomic number 75 was isolated in an impure state Eka-manfrom manganese preparations. ganese has also been announced and the discovery of the rest has been foreshadowed in the Chemical News. The The importance of X-ray spectra in this field can hardly be over-estimated. rare earth group of elements has long been one of the difficulties of chemical science and the definite proof of the exact number of these metals has eliminated the possibility of much valuable time and energy being lost in a futile search for others. In the Periodic Classification, following barium, are the so-called rare earths (except scandium and yttrium). They were originally found in Scandinavia, but deposits have since been exploited in other parts of the world, especially America. Their separation and the elucidation of their chemistry has proved tedious, but is now fairly well known. Prof. Stewart's account of these metals constitutes a valuable section of his book and his method of placing them in the Periodic System has much to commend it. Urbain's work on the rare earths led to the view that element of atomic number 72 would belong to that group. The substance isolated by Coster and Hevesy, however, shows close similarity in properties with zirconium, with which it is associated in zircons and it undoubtedly belongs to the fourth group. Hafnium can be separated from zirconium either by taking advantage of the difference in basicity between the oxides or by utilising the different solubilities of the double potassium fluorides. Other hafnium compounds very closely resemble those of zirconium in properties. Its atomic weight has been determined and the value is near 180. In the references to hafnium, Prof. Stewart makes no mention of the several important communications from Coster and Hevesy, and Hevesy and Jantzen, which have appeared in the Chemical News. Varieties of active hydrogen and nitrogen have been prepared recently. Active hydrogen appears to be triatomic since contraction occurs during its preparation, on that account has been termed hyzone. It reduces sulphur, arsenic, potassium permanganate, and other substances. It is changed into diatomic hydrogen by catalysts like platinum and nickel, although con THE LAW OF HEAT OF FORMATION. By HAWKSWORTH COLLINS, B.A. (Camb.). This law was first published in the Chemical News, 1922, CXXV., 81. Since then a great many confirmations of it have appeared in the same periodical, but they are scattered abount in twenty-six papers, so that it seems advisable now to bring them all together (before continuing the demonstration for each element) in order that scientists may see that the law is true without any doubt whatever, being supported by an overwhelming number of facts. The law is as follows: "The heat of formation of an element is proportional to the product of its change of volume and its atomic weight, there being two distinct series, the sodium elements and the sub-sodium elements." Sub-sodium elements are those of atomic tact with a number of metals does not affect it. Strutt's active nitrogen reacts with phosphorus vapour, sulphur, and many metals when warmed, with the formation of nitrides. Much work has been done recently upon the hydrides and most of this receives adequate and careful treatment in the volume under review, but the author seems unaware of the existence of the solid hydrides or arsenic, antimony and bismuth, whose modes of preparation have been described during the last few years in this Journal, the Transactions of the Chemical Society, and the Recueil de Travaux chimiques des Pays-Bas. Whilst reference, and perhaps emphasis, has been laid upon some of the omisions in Prof. Stewart's Recent Advances, it should be pointed out that these scarcely detract from its great value. Much important matter contained within the 300 odd pages cannot be mentioned, even in a lengthy notice, but it is hoped that sufficient has been said to indicate that the book includes the results of researches over the whole field of Physical and Inorganic Chemistry. Successive editions of Prof. Stewart's Recent Advances have enjoyed a considerable vogue, not only among college students, but among chemists generally, for they have become indispensable to all interested in recent work and progress in chemical science. weight less than 22. J. G. F. DRUce. Sodium elements are those of atomic weight greater than 22. 66 Change of volume means the difference between the combining volume and the original free volume. When the former is less than the latter, the H.F. is positive, and when the former is greater than the latter the H.F. is negative. There is room for only one example of each case, but an extra one is given when considered necessary. Table I. gives the original relative volume of each one of 32 elements, obtained by dividing the atomic weight (see Table IV.) by the theoretical specific gravity. The original volumes required by the law for Ag and Al occur in alloys. For Cl, 0 and N the equivalent original volumes are given, i.e., the volumes these elements would have in the free state if they were solid instead of gaseous. The original volumes obtained for Ba, Mg, Mn, K and |