September 12, 1895] 



NATURE 



481 



the British Association, that mixed diazoamides may be deriva- 

 tives of such a 4-atom ring. 



Any chemist who has followed the later developments of the 

 chemistry of nitrogen could supply numerous other instances of 

 undiscovered types. A chapter on the unknown compounds of 

 this element would furnish quite an exciting addition to many 

 of those books which are turnetl out at the present time in such 

 profusion to meet the requirements of this or that examining 

 body. I have selected my examples from these compounds 

 sim]>ly because I can claim some of them as personal acquaint- 

 ances. It would be easy to make use of carbon compounds for 

 the same purpose, but it is unnecessary to multiply details. It 

 has frequently happened in the history of science that a well- 

 considered statement of the shortcomings of a theory has led to 

 its much-desired extension. This is my hope in venturing to 

 point out one of the chief deficiencies in the structural chemistry 

 of the present time. I am afraid that I have handled the case 

 badly, but I am bound to confess that I am influenced by the 

 same feelings as those which prevent us from judging an old and 

 well-tried friend too severely. 



The theory of types to which we have reverted as the outcome 

 of the study of molecular structure is capable of almost indefinite 

 extension if, as there is good reason for doing, we replace atoms 

 or groups by their valency analogues in the way of other atoms 

 or groups of atoms. The facts that in cyclic systems X can re- 

 place CH (benzene antl pyridine), that O, S, an'l Nil are 

 analogues in furfurane, thiophene. and pyrrole, are among the 

 most familiar examples. The remarkable iodo- and iodoso- 

 com(X)unds recently discovered by X'ictor Meyer and his col- 

 leagues are the first known instances in which the trivalent atom 

 of iodine has been shown to be the valency analogue of nitrogen 

 in organic combination. Pushing this principle to the extreme 

 we get further suggestions for new groupings, but, as before, no 

 certainly of prevision. Thus, if nitrogen formed the oxide NoOj 

 the series might be written : 



N. 



N 



O O 





N :0 



O or 







/ 



N-O 



or O 



N: O 



^N-O 



N :0 



& 

 N:0 



&c. 



Of course these formulae are more or less conjectural, being based 

 on valency only. But since nitrous oxide is the analogue of 

 hydrazoic acid, they hint at the possibility of such compoimds as 



1 1 NY 



\ 



N' 



)NII, &c. If a student produced a set of formuUe 



corresponding to the above, in which Nil had been substituted 

 for f), and asked whether they did not indicate the existence of 

 a whole series of unknown hydrogen compounds of nitrogen, we 

 should probably tell him that his notions of chemical structure 

 had run wild. At the same time I am bound to admit that it 

 would be very difficull, if nw^t impossible, to furnish him with 

 satisfactory reasons for believing that such groupings are 

 improbable. Compare again the series : 



0:C/ '(i)0:C/| (2) 0:C< -(3) 0:C<; (4) 



-/ 



NIU 



^\H 



\nii„ ^nii 



/N /NO, 



(6) H.,C<-{7) IUC< (8) 

 ^N \nO„ 



The first is urea ; the second, third, fourth, fifth (methylene 

 diamine), and sixth are unknown ; the seventh is the remarkably 

 interesting diazomethane discovered last year by II. v. Pech- 

 mann {Ber.y 27, 18SS). The last comjiound, dinitromethanc, is 

 known in the form of its salts, but appears to be incapable of 

 existence in the free state. There is nothing expressed or 

 implied in the existing theory of chemical structure to explain 

 why dinitromethanc is unstable while trinilromethanc is stable, 

 ami mono- and tetranitromethane so stable as to admit of being 

 distilled without decomposition. Chemists will form their own 

 views as to the possibility or impossibility of such a series as 

 this being completed. Whether there would be a concordance 

 of opinion I will not venture to say ; but any chemist who ex- 

 pressed either belief or disbelief with regard to any special 

 member would, I imagine, have great ditiiculty in giving a 

 scientific reason for the faith which is in him. At the most, he 

 would have only the very unsafe guide of analogy to fall back 

 upi>n. Perhaps by the time the British Association holds its 

 next meeting at Ipswich it will have become possible to prove 

 that one particular configuration of certain atoms is passible and 



NO. 1350, VOL. 52] 



another configuration impossible. Then will have been achieved 

 that great advance for which we are waiting — the reunion of the 

 two streams into which our science began to diverge shortly after 

 the last Ipswich meeting. 



The present position of structural chemistry may be summed 

 up in the statement that we have gained an enormous insight 

 into the anatomy of molecules, while our knowledge of their 

 physiology is as yet in a rudimentary condition. In the course 

 of the foregoing remarks I have endeavoured to indicate the 

 direction in which our theoretical conceptions are most urgently 

 pressing for extension. It is, perhaps, as yet premature to pro- 

 noimce an opinion as to whether the next development is to be 

 looked for from the stereochemical side ; but it is not going too 

 far to express once again the hope that the geometrical repre- 

 sentation of valency will give us a deeper insight into the con- 

 ditions which determine the stability of atomic configurations. 

 The speculations of \. v. Baeyer, Wislicenus, \ictor Meyer, 

 Wunderlich, Bischoff, and others have certainly turned the 

 attention of chemists towards a quarter from which a new light 

 may eventually dawn. 



The Progress of Syntheticai, Chemistry. 



If, in my earnest desire to see the foundations of structural 

 chemistr)' made more secure, I may have unwittingly given rise 

 to the impression that I am depreciating its services as a scientific 

 weapon, let me at once hasten to make amends by directing 

 attention to the greatest of its triumphs, the synthesis of natural 

 products, i.e. of compounds which are known to be produced 

 by the vital processes of animals and plants. 



Having been unable to find any recent list of the natural com- 

 pounds which have been synthesised, I have compiled a set of 

 tables which will, I hope, see the light at no ver>' distant period. 

 According to this census we have now realised about 180 such 

 syntheses. The products of bacteria have been included in the 

 list because these compounds are the results of vital activity in 

 the same sense that alcohol is a product of the vital activity of 

 the yeast plant. On the other hand the various uro-compounds 

 resulting from the transformation in the animal economy of 

 definite chemical substances administered for experimental pur- 

 poses have been excluded, because I am confining my attention 

 to natural products. Of course the importance of tracing the 

 action of the living organism on compounds of known constitu- 

 tion from the physiological point of view cannot be overestimated. 

 Such experiments will, without doubt, in time shed much light 

 on the working of the vital laboratory. 



The history of chemical synthesis has been so thoroughly dealt 

 with from time to time that I should not have ventured to 

 obtrude any further notice of this subject ujion your patience 

 were it not for a certain point which appeared to me of sufficient 

 interest to merit reconsideration. It is generally stated that the 

 formation of urea from ammonium cyanate by Wohler in 1S2S 

 was the first synthesis of an organic compound. There can be 

 no doidjt that this discovery, which attracted much attention at 

 the time, gave a serious blow to the current conceptions of 

 organic chemistry, because urea was so obviously a product of 

 the living animal. It will be found, however, that about the 

 same time Henry Hennell, of Apothecaries' Hall, had really 

 effected the synthesis of alcohol— that is to say, had synthesised 

 this compoumi in the same sense that Wohler had synthesised 

 urea. The history is soon told. In 1826 Hennell (through 

 Brande) communicated a paper to the Royal Society which 

 appears in the Philosophital Tmnsaitions for that year.' In 

 studying the compounds produced by the action of sulphuric acid 

 on alcohol, and known as " oil of wine,"' he obtained sulpho- 

 vinic acid, which had long been known, and gave fairly good 

 analyses of this acid and of some of its salts, while expressing in 

 the same paper very clear notions as to its chemical nature. 

 Having satisfied himself that sulphovinic acid is a product of the 

 action in question, he then proceeded to examine some sulphuric 

 acid which had absorbed eighty times its volume of defiant gas, 

 and which had been placed at his disposal for this purpose by 

 Michael 1-araday. Krom this he also isolated sulphovinic acid. 

 In another paper, communicated to the Royal Society in 1828,- 

 he proves quantitatively that when sulphovinic acid is distilled 

 with sulphtiric acid and water the whole of the alcohol and sul- 



1 "On the Mutual Action of Sulphuric Acid and Alcoliol, with Observa- 

 tions on the Composition and Properties of the resulting compound," FhiL 

 Trans.. 1826, p 240. 



2 " On the Mutual .\ction of Sulphuric .\cid and Alcohol, and on the 

 Nature of the I*roccss by which Ether is formed," Phil. Trans. ^ 1828, 

 P- 3^5- 



