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XXVII. On the Tetravalency of Oxygen ; with Remarks on 

 the Varying Valency of the Elements and the Present Chemical 

 Aspect of the Valency Problem. By J. F. Heyes, M.A., 

 F.C.S., F.R.G.S., of Magdalen College, Oxford*. 



THE actual state, or rather phase, of philosophic Chemistry 

 presents us with a remarkable paradox. Simultaneous 

 with the discovery and chemical analysis of countless new 

 compounds and many new elementary or non-resolved sub- 

 stances during the present century, there have emerged a 

 series of views on the constitution of matter and the cor- 

 relation of material forces which will for many centuries 

 to come mark the greatest epoch in scientific philosophy. 

 Although this molecular theory of matter has been chiefly 

 developed on the physical and dynamical side, the con- 

 tributions from the chemical side of the hedge of this 

 great field of research have been very striking — such, in 

 fact, as to stimulate the work of our greatest physicists. 

 Scientific chemists, it may be said, have established the law 

 of the conservation of mass ; physicists, that of energy : now 

 both are united in searching out the nature and influences 

 of the masses and forces which are at work in the material 

 world of chemical substances. But while the smaller limit, 

 so to speak, of physical analysis is the molecule, it forms the 

 upper limit of chemical analysis and synthesis. The main 

 studies of the physicists are inter-molecular, those of the 

 chemists intra-molecular phenomena. From this point of 

 view, strict Chemistry begins where Physics ends ; but, 

 viewed historically, a growing interaction must be con- 

 fessed, and, indeed, a friendly struggle has begun for the 

 wells of the border-land which the one side calls molecular 

 physics and the other physical chemistry. Both are pecu- 

 liarly interested and puzzled just now in what are somewhat 

 curiously termed "molecular compounds" or aggregations. 

 Undoubtedly the trouble is chiefly and naturally on the 

 chemical side ; and, in the conventional system of shorthand 

 or formulae which the chemist uses to express (1) his facts 

 about their composition and (2) his views about their con- 

 stitution, it may be said to take the form of a discussion 

 as to the meaning of certain dots and dashes with which our 

 new text-books are plentifully (and to many students, I fear, 

 misleadingly) sprinkled. 



If, therefore, in calling attention to the question of the 

 * Communicated by the Author. Read before the Ashuiolean Society, 

 Oxford, 7th November, 1887. 



