M 



NATURE 



[December 29, 192 1 



the individual and the race, it was, in a sense, forced 

 on them. It was thus in conflict with the idea of 

 the freedom of artistic activity — the corner-stone of 

 current artistic theory. Mr. Miles Burkitt described 

 the new painting of Palaeolithic age found in the 

 Pvrenean cave of Trois Freres. The painting por- 

 trays a number of animals arranged as a frieze and 

 the figure of a masked man with stag's antlers on 

 his head and with a tail which the author compared 

 with the early Gallic god, always shown as masked, 

 and the Cretan god of Minoan times. This figure 

 elicited some interesting remarks from Miss Murray 

 on the possible existence of a witch-cult in Palaeo- 

 lithic times. Mr. Leslie Armstrong exhibited a re- 

 prcxiuction of the engraved flint found last year at 

 Grime's Graves. 



As a preliminary to the excursion made by 

 members of the section to the excavations on Traprain 

 Law, Mr. Alex. O. Curie gave an account of the 

 earthworks and settlements on this site, and described 

 the magnificent hoard of fourth-century silver plate 

 discovered there and believed to have formed part 

 of the booty pillaged by Saxon pirates from Gaul. 



Among other communications on archaeological sub- 

 jects mention must be made of Miss Murray's account 

 of her investigations in Malta, which brought to light 

 the site of a megalithic temple at Boy en Nadur, on 

 the Bay of Marsa Scirocco, and Dr. T. Ashby's account 

 of the year's work in Italy and Tunisia, which has 

 given us, particularly at Ostia and Pompeii, much 

 fresh evidence as to Roman domestic architecture. 

 Mr. J. Whatmough dealt with the functions of the 

 Rehtia, the Venetic goddess of healing, suggesting 

 that the so-called '"nails" and "wedges" associated 

 with the cult are to be explained as a specialised type 

 of votive hair-pins with pendant axe-shaped talismans. 



Mr. Stanley Casson gave a descriptive account of 

 a journey through Macedonia undertaken under the 

 auspices of a committee of the Association with a 

 view to archaeological investigation. Excavations of 

 a cemetery at Chauchitsa produced a large number 

 of objects of the Iron age, including bronze orna- 

 ments, pottery, hand- and wheel-made, some gold, 

 and a little iron. These finds throw an interesting 

 light upon the culture of Macedonia and its relations 

 with Greece at this period. 



Valency Bonds and the Mechanism of Organic Reactions. 



I 



N recent vears the significance of the conventional 

 bond in the structural formulae of organic com- 

 pounds has been the subject of much speculation, 

 more particularly in reference to the view that the 

 bond corresponds with the field between two opposite 

 electrical charges associated with the chemically com- 

 bined atoms. The electrical conception of the valency 

 bond has been further developed in a very interesting 

 manner by Prof. A. Lapworth (Manchester Memoirs, 

 vol. 64, No. 3, 1920) with the object of explaining the 

 mechanism of the reactions of organic compounds. 



Certain reactions, such, for example, as those of 

 carbonyl compounds with electrolytes, suggest that the 

 carbon atom of the carbonyl group is more electro- 

 positive than the oxygen atom of this group, in that 

 the carbon atom invariably enters into combination 

 with the negative ion. The relative polar character 

 which the two atoms seem to display at the moment 

 of chemical change mav thus be indicated by ascribing 

 -f and — signs to the carbon and oxvgen atoms 

 respectivelv. Other reactions — for example, the aldol 

 reaction— suggest that the hydrogen atom in the group 

 XH'CO- is positive relatively to the carbon atom 

 with which it is in combination, and it would there- 

 fore seem that the group in question can be repre- 

 sented bv the formula 



V I 



H-c-c:o 



in which the contiguous carbon atoms have opposite 

 polarities. There is a good deal of evidence in favour 

 of the existence of such latent polarisation in pairs of 

 contiguous carbon atoms, and of the view that the 

 carbonyl group tends to develop alternate negative 

 and positive polarities in all the carbon atoms of any 

 chain with which the carbonyl group is associated. 



Similar efl'ects are produced by the 'NO,, 'SO,*, 

 and 'CN groups, and it would seem that the divalent 

 oxygen and tervalent nitrogen atoms are the directing 

 or "key atoms" to which the development of the 

 alternating latent polarisation is to be referred. The 

 halogens are much less effective than oxygen and 

 nitrogen, whilst hydrogen apparently exercises a 

 perceptible influence of the opposite kind. 



The extension of the influence of the "key atom " 

 over any considerable range seems to require for its 

 fullest display the presence of double bonds, usually 

 NO. 2722, VOL. I08I 



in conjugated positions. The conjugated structure of 

 aromatic compounds affords ample scope for the 

 directing influence of the "key atom," and the be- 

 haviour of aromatic compounds is quite in accordance 

 with the predictions of the underlying general prin- 

 ciple to which Lapworth has given the name of the 

 "principle of induced latent polarities." It is shown 

 that this principle affords a very plausible explanation 

 of many groups of well-known reactions. 



The mechanism of organic reactions is also dealt 

 with in the same volume (No. 4) by Prof. R. Robinson 

 in a paper on "The Conjugation of Partial Valencies." 

 The views put forward by this author have a close 

 connection with the above theory of the development 

 of latent atomic polarisation bv induction. It is 

 assumed that reactive (activated) molecules are those 

 in which a rearrangement of valencies or a change 

 in the position of the electrons has taken place. Such 

 rearrangement or change in position is synonymous 

 with the development of partial valencies. To illus- 

 trate by a simple example, it is suggested that whereas 

 the normal molecule of hvdrogen chloride is repre- 

 sented bv the formula H-Cl, the activated molecule 



is symbolised by • •, • H • • • • CI • • •, in which the dotted 



+ - 



lines represent partial valencies of which that of 

 hydrogen is positive and that of chlorine is nega- 

 tive. The author shows that the mechanism of many 

 important reactions can be readilv interpreted in terms 

 of such activated molecules. In particular, mention 

 mav be made of the phenomena of conjugation, the 

 representation of which is considerably simplified, 

 whilst at the same time the conception of a con- 

 jugated system is widely extended. From the 

 author's point of view, conjugation consists, in fact, 

 of the transfer of a free partial valency (or latent 

 polarity) to an adjacent carbon atom or to other 

 carbon atoms more widelv remo\"ed, and in theory 

 there is no limit to the transmission of reactivity 

 within the limits of the molecular aggregates. 



Whether it is preferable to speak of the induction 

 of latent polarisation or the transfer of partial 

 valencies is not a matter of the first importance; it 

 mav be taken for granted, however, that the views 

 outlined bv Lapworth and Robinson will be of great 

 value in obtaining further insight into the mechanism 

 of the reactions of organic compounds. 



H. M. D. 



