NA TURE 



457 



THURSDAY, MARCH 17, 1898. 



THE CHEMISTRY OF THE METALS. 



A Treatise on Chemistry. By H. E. Roscoe and C. 

 Schorlemmer. Vol. il. The Metals. New edition 



completely revised by Sir H. E. Roscoe, assisted by 

 Drs. H. G. Colman and A. Harden. Pp. 1 192. 



CLondon : Macmillan and Co., Ltd., 1897.) 



NEARLY twenty years have elapsed since the 

 appearance of this part of Roscoe and Schor- 

 lemmers well-known treatise, and as in the interval 

 much important work has been done in connection with 

 the classification of the elements, with metallurgical 

 processes, with chemical manufactures and new theories 

 bearing upon our views of the constitution of salts, the 

 condition of dissolved substances and other important 

 questions have been proposed, it is obvious that the time 

 has come when a new edition is urgently needed. It 

 may at once be said that the revision has been accom- 

 plished with great care, with full knowledge, and, speak- 

 ing generally, with a great measure of success. 



The introductory chapters, which occupy 150 pages, 

 naturally contain the most debateable matters, concern- 

 ing which, probably, there will always be considerable 

 differences of opinion, relating as they do to such sub- 

 jects as the characteristics of metals, to valency, to 

 classification and other subjects which are less matters 

 of fact — for there is usually not much dispute about the 

 facts — than of inference, and must therefore assume 

 different aspects according to the degree of importance 

 with which they are invested in different minds. 



Take, for example, the consideration of those pro- 

 perties of the metals which seem to some people to mark 

 off these substances very clearly from the remaining 

 elements, which are commonly referred to as non-metals. 

 Of course any attempt to arrange natural things into 

 groups, the members of every one of which are dis- 

 tinguishable sharply from the members of other groups, 

 fails hopelessly when such attempt is carried too far ; 

 but this need not prevent such attempts from reaching 

 that measure of partial success which is practically 

 useful. It is, in fact, impossible to avoid classification, 

 for no sooner does a series of facts or phenomena become 

 known than the mind involuntarily proceeds to arrange 

 them into groups, and the pretence on the part of a few 

 modern chemists that no scientific distinction can be 

 drawn between metals and non-metals is not likely to be 

 permanently maintained. The want of definiteness on 

 this point in the book before us is to be regretted. We 

 aie told (pp. 5, 6) that "although the division into 

 metals and non-metals is thus seen to be one which does 

 not admit of exact definition, it is none the less true that 

 the metals as a class do possess certain generic properties 

 which the non-metals either do not possess at all or 

 exhibit only in a very slight degree," and it is a little 

 surprising to find that " among these properties that of 

 metallic lustre may be specially mentioned." What 

 then about iodine, graphite apd tellurium, which most 

 people agree to place among non-metals ? 

 NO. 1 48 1, VOL. 57] 



Undoubtedly any attempt to provide a definition which 

 shall be comprehensive enough to include not only 

 the seven ancient metals, but such things as arsenic, 

 antimony, titanium, as well as the true metals — sodium 

 and the rest which have been made known in modern 

 times — must fail ; but that is not a reason for refusing 

 to recognise in the great majority of those elements 

 which show a disposition to form oxides of more or less 

 prqnounced basic character, certain other characters, 

 chemical and physical, which, taken together, afford a 

 useful criterion of the true metal, while for those elements 

 which only imitate the metals in one character or more 

 and fail in the rest, the term " metalloid," so long mis- 

 applied, might be appropriately retained. The true 

 metal is malleable, with a good conducting power for 

 heat and electricity, and forms no gaseous or vaporisable 

 compound with hydrogen. The semi-metal or metalloid 

 is brittle, a bad conductor, and in many cases produces 

 a gaseous hydride. 



The general adoption of iMendeleeff's scheme of 

 classification of the elements has no doubt served to 

 increase the difficulty felt as to the distinction of metal 

 from non-metal ; but even in the periodic table the non- 

 metals are confined to the top right-hand corner, and 

 display amid great physical diversity an assemblage of 

 chemical characters which marks them off as a class. 



Naturally there are elements which recall in respect 

 to one set of relations the features of a metal, and in 

 respect to another those of a non-metal, and these of 

 course stand between ; but to refuse to recognise these 

 distinctions would be as inconvenient as a proposal to do 

 without "orders" in botany because all botanists are 

 not agreed about the diagnostic characters of every 

 order in the vegetable world. 



The authors have made a change of some importance 

 in the sequence in which the metallic elements are taken 

 for study in this volume. In the first edition they were 

 grouped into families more or less entitled to be regarded 

 as "natural"; but are now taken in the order of the 

 periodic system. There is, however, a sort of acknowledg- 

 ment of the inconvenience of this plan for the arrange- 

 ment of matters for study, inasmuch as it is departed 

 from at the very outset, sodium and not lithium being 

 the metal first described. It must, however, be admitted 

 that the authors have dealt with this difficult question in 

 the liberal spirit proper to scientific men. They point 

 out that while the arrangement of the elements in the 

 order of their atomic weights has brought into view the 

 remarkable relations among their properties which are 

 formulated in the so-called " periodic law," and that this 

 system stands upon a very firm basis of fact, 



"the system will doubtless undergo modification as 

 our knowledge increases, for difficulties occur which 

 cannot at present be explained. Thus elements some- 

 times occur in the same group between which only a 

 limited amount of analogy can be traced and, on the 

 other hand, elements which have a good deal in common 

 are sometimes separated widely." 



This being admitted, it is a very doubtful advantage to 

 have adopted the system, interesting and suggestive as 

 it is, as the order for the contents of the book. This, 

 however, is not of serious consequence inasmuch as the 



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