28o 



NA TURE 



[September 2, 1909 



Our present conception is that the carbon atom has 

 tetrahedral properties in the sense that it has four affinities 

 which operate practically in the direction of the four radii 

 proceeding from the centre towards the four solid angles 

 of a regular tetrahedron. 



More than analogical significance — to use Larmor's ex- 

 pression — must be accorded to this symbol on account of 

 its remarkable accordance with the facts generally, whether 

 derived from the study of asymmetric optically active sub- 

 stances or from observation of the activity of ring structures 

 of various degrees of complexity. Nothing is more sur- 

 prising than the completeness with which the vast array of 

 facts included in organic chemistry may be ordered by 

 reference to the tetrahedral model. In the future, when 

 our civilisation is gone the way of all civilisations and 

 strangers dig on the sites of our ruined cities for signs of 

 our life, they will find the tetrahedron and the benzene 

 hexagon among the mystic symbols which they have diffi- 

 culty in interpreting ; if, like the ancient Egyptians, we 

 made our tombs records of our wisdom, such symbols would 

 long since have acquired sacred significance and the public 

 would probably have learnt to regard them with awe and 

 to respect them as totems. Chemists might at least wear 

 them on aprons in imitation of the Freemasons ; perhaps 

 no two other symbols have so great a significance — tlioy 

 reach into life itself. 



It would seem that carbon has properties which are alto- 

 gether special, the influence which it exercises upon other 

 elements in depriving them of their activity is so remark- 

 able. In their recent discussion of the relation of crystal- 

 line form to structure, in which valency is represented as a 

 function of the volume sphere of influence exercised by an 

 element, Barlow and Pope arrive at the remarkable con- 

 clusion that carbon is probably the only element the atom 

 of which has a volume sphere of inlluence four times that 

 of the hydrogen atom ; although it combines with four 

 atoms of hydrogen, silicon apparently has only half the 

 volume sphere of influence of carbon. This may, in a 

 measure, account for the very great dissimilarity in 

 behaviour of the two elements, which is most pronounced 

 in their oxides, the single atom of carbon all but dominating 

 two atoms of o.xygen in carbon dioxide (which is conse- 

 quently gaseous), whilst the atom of silicon in silicon 

 dioxide in no way eclipses the two atoms with which it is 

 associated but leaves both charged with residual affinity 

 which enables them to form complex collocations of re- 

 markable fixity in the fire. At bottom the differences 

 between organic and inorganic nature arc to be regarded 

 as very largely the expression of this difference. Ropes of 

 sand are proverbially treacherous ; yet without sand, if 

 silica had been a gaseous substance, our world might have 

 worn a strangely different aspect.' 



The mineral world apparently owes its rigidity to the fact 

 that the metals and certain other elements are so imper- 

 fectly capable of dominating oxygen that oxides generally 

 polymerise with great readiness, giving rise to substances 

 which do not even fuse easily. The organic, on the other 

 hand, appears to be plastic by reason of the close approach 

 to neutrality which is conditioned by association with 

 carbon. 



Nothing is more striking than the remarkable diversity 



1 The solid model of silica which Barlow and Pope have constructed has 

 very remarkable attributes, in that the oxj-gen atoms appear to be iinitormly 

 related and in intercommunication throughout its mass : so that a mass of 

 silica, whatever its size, may almost be regarded as a single molecular com- 

 plex. A similar view may be taken of the plastic metals such as those of the 

 platinum group, gold, silver and copper. Whether when rendered brittle by 

 association with small amounts of impurity these are resolved into simpler 

 molecular complexes or whether the molecules merely become separated by 

 substances which promote discontinuity and brittleness, it is impossible to 

 say at present. The cause of hardness in mineral materials is, however, a 

 question of no slight interest and importance. The property is strikingly 

 exemplified in the diamond. It is difficult to understand the intense hard- 

 ness of this material, on the assumption that the diamond is composed of 

 paraffinoid carbon — that is to say, carbon with all its affinities satisfied. At 

 present we appear to have no clue to the manner in which affinity acts in 

 promoting the formation of such solids. But it is obvious that all solids are 

 possessed of some degree of " surface affinity," as they not only grow when 

 placed in solutions but determine the separation of solid from a solution at a 

 degree of saturation which is often considerably below that at which the 

 solution is actually saturated with the substance ; and such surface affinity, 

 moreover, is selective, as the determinative effect is exercised only upon the 

 substance itself or substances isomorphous with it — although exception must 

 be made in favour of water, which all surfaces appear to attract. Sir James 

 Dewar's observations on the condensation of gases by charcoal at low tem- 

 peratures afford most striking illustrations of surface affinity. 



NO. 2079, VOL. 81] 



of properties manifest both in the materials which at pre- 

 sent we are content to call elements and in the coinpounds 

 formed by their interaction ; the range of variation met 

 with in the case of the compounds of carbon with hydrogen 

 and oxygen alone is almost infinite. We are almost com- 

 pelled to attribute this diversity more to differences in the 

 complexity and structure of the inolecules than to differ- 

 ences in their material composition. The chemist, of neces- 

 sity, must be a dreamer, knowing as he does that things 

 are not as they seem to be. But this is not sufficiently 

 remembered ; indeed, students are systematically trained up 

 in an atmosphere of pretence. The beginner is allowed to 

 regard elementary oxygen, for example, as a colourless gas, 

 which is generally harmless until things are presented to it 

 in a more or less heated condition, whereat it takes umbrage 

 and burns them up. He wpuld regard elementary carbon 

 as a soft black substance, which if smeared on the face of 

 the white man makes him look like a nigger, were it not 

 that he also learns that at times it is the hardest and 

 whitest substance known ; of organic chemistry, which alone 

 can give hitn honest ideas of carbon, he is not allowed to 

 hear, as I have said. The sting of awakening conscience 

 is salved by the introduction of a long Greek word when 

 he is told that the two substances, soot and diamond, are 

 allotropic forms of the element carbon ; nevertheless, he re- 

 gards them both as elementary carbon. Gradually, perhaps, 

 he awakens to a sense of the w-rong that he has suffered at 

 the hands of his teachers, as he realises that from no one 

 substance can he gather what the properties of an element 

 are, that after all the efementary substance is but an ideal 

 — in other words, a mere concept. If appreciative, he then 

 learns to think of the blandness of water, the sweetness of 

 sugar, the sourness of vinegar, the causticity of soda, in- 

 deed every distinctive property of every known oxygen 

 compound as more or less a property of, more or less 

 conditioned by, the element oxygen ; he is brought back, 

 in fact, to the position from which Lavoisier started, as he 

 realises that the oxygen gas which he inhales is not 

 elementary oxygen ; he can then perhaps appreciate the 

 wonderful acumen which this greatest of chemical philo- 

 sophers displayed when he wrote : " Nous avons donn^ a la 

 base de la portion respirable de I'air le nom d'oxyg^ne erk 

 le derivant de deux mots grecs ofiJs, acide, yeivofiai, 

 j'engendre, parce qu-en effet une des propri^t^s les plus 

 g^n^rales de cette base est de former des acides en se coni- 

 binant avec la plupart des substances. Nous appelerons 

 done gaz oxyg^ne la reunion de cette base avec le calorique." 

 We have allowed a century to pass without recognising the 

 wonderfully accurate powers of prevision displayed by 

 Lavoisier ; what is worse, we have been so far led astray 

 that instead of regarding oxygen as the characteristic and 

 attractive elements in acids, hydrogen has been allowed to 

 usurp the position : the extent to which the cult of the 

 hydrogen ion now dominates the text-books is well known ; 

 in davs to coine, when the history of our times is written, 

 it will be referred to as a remarkable example of chemical 

 shortsightedness. 



Names are needed for the elements which would serve to 

 distinguish the ideal elementary substances from the forms 

 in which they are known to us. No more appropriate 

 name than oxygen could possibly be selected for the funda- 

 mental material; if the gen terminal could be applied to 

 elementary materials generally, it would be an advantage ; 

 it would not be easy, however, if this were done, to devise 

 an appropriate separate name applicable to the active con- 

 stituent of air.' 



1 In naming the inert gas in air, which he ultimately termed azotic g-as, 

 having proposed the name azoic for the element, Lavoisier had in view as 

 alternatives the terms akatigen and nitrogen. As there was no proof that 

 the element was a constituent of alkalies other than ammonia, he rejected 

 the former name on the ground that it might convey too broad an impres- 

 sion ; in course of time the latter is become the popular name, except \n 

 France, where motives of piety have prevailed ; but the French practice has 

 been justified by the universal use of the term azo in connection with many 

 nitrogen derivatives. 



Had Lavoisier realised that the alkalies and basic oxides generally owe 

 their basicity to oxigen as much as acids and acidic oxides generally owe 

 their acidity to oxygen — the one being oxygen tempered by metal, the other 

 oxygen tempered by non-metal — as the number of basic oxides far outweighs 

 the number of acidic oxides, he might well have chosen the name alcaligen 

 rather than oxygen. The choice he made was a particularly happy one and 

 striking evidence of his genius and sense of euphony — for oxygen is pfrr 

 excellence the acid-forming element and is most truly called soiir-stujff, the 

 stuff of which .sour things are made — for whatever the properties of the 



