648 - KEPORT— 1895. 



possibility of such compounds as HN^ • ^NH, &c. If a student produced a set 



of fcrmulse corresponding to the above, in which NH had been substituted for 0, 

 and aslied whether they did not indicate the existence of a whole series of unknown 

 hydrogen compounds of nitrog-en, 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 difficult, if not impossible, to furnish him with satisfactory reasons 

 for believing that such groupings are improbable. Compare again the series: 



O : c<5;S= (1) o : c/j||(2) o : c<^. (3) o : c/^JJO^^ (4) 



H=<SS:(5) KX<(r(G) H,c/^.(7) HX<N0.(8) 



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 H. v. Pechmann.^ The last compound, dinitroinethane, 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 existinij- theory of chemical 

 structure to explain why diuitromethane is unstable while trinitromethane is 

 stable, and mono- and tetranitromethane so stable as to admit of being distilled 

 without decomposition. Cliemists 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 expressed 

 either belief or disbelief with regard to any special member would, I imagine, have 

 great difficulty in giving a scientific reason for tlie faith which is in him. At the 

 most, he would have only the very unsafe guide of analogy to fall back upon. 

 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 possible and 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 maj' be summed up in the state- 

 ment 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 Ibregoing 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 prouoimce an opinion as to whether the next de- 

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

 far to express once ag«iu the hope that the geometrical representation of valency 

 will give us a deeper insight into the conditions which determine the stability of 

 atomic configurations. The speculations of A. v. Baeyer, ■\^'islicenus, Victor 

 Meyer, "Wunderlich, Bischoft", and others have certainly turned the attention of 

 chemists towards a quarter from which a new light may eventually dawn. 



The Pkogeess of Synthetical Chemistrt. 



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

 more secuie, I may have unwittingly given rise to the impression that 1 am de- 

 preciating 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 pro- 

 ducts, 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 compounds which 

 have been synthesised, I have compiled a set of tables which will, I hope, see the 



' Ber., 27, 1888. 



