158 Professor M. 0. Forster [May 5, 



accomplished by a process due to Noeltiug, which consists in adding 

 sodium azide to the diazonium sulphate : 



X-N.-HSO, + NaNg = X'Ng + N, + NaHSO^. 



The remarkable instability of the diazonium azide, upon which 

 this reaction depends, recalls that of the diazonium iodide, following; 

 which the iodine atom may be introduced into a benzenoid compound, 

 and incidentally offers one more analogy between the triazo-group 

 and a halogen. Moreover, resemblance to the haloid elements is 

 suggested not only by this method of introducing an azoimide 

 complex into the aromatic nucleus, but also by the circumstances 

 attending its removal. It is well known that a chlorine atom in the 

 benzene ring is so firmly attached that it cannot be removed by hot 

 caustic alkalis, but that if nitro-groups also are present in the ortho- 

 and para-positions, the halogen may be removed quite easily, so that 

 picryl chloride is converted into picric acid by the action of water. 

 Very similar relationships prevail among the substituted azoimides of 

 benzene and naphthalene, from which hydrazoic acid may be eliminated 

 according to well-defined principles. 



It is now six years since we were led, at the Royal College of 

 Science, to a study of the triazo-group by the accidental discovery of 

 triazocamphor, a substance wbich displays properties in some respects 

 novel, and in this connexion it gives me the greatest pleasure to 

 acknowledge that the development of the subject has been in a large 

 measure due to the courage and ingenuity displayed in its early 

 stages by my former colleague, Dr. H. E. Fierz. The majority of 

 the new materials differ from those of previous workers in belonging, 

 not to the aromatic series, but to the other great class of organic 

 substances, the ahphatic derivatives. It is with a study of the 

 general behaviour of the triazo-group in the diverse environment 

 afforded by these two classes that we have been concerned, and with 

 this object have prepared azoimides of such simple types as acetalde- 

 hyde, acetone, acetic acid, ethyl acetate, acetamide, ethyl alcohol, ethyl 

 ether, substituted malonic acids, the unsaturated hydrocarbons ethy- 

 lene and propylene, and, lastly, ethylamine. To these have been 

 added certain bistriazo-compounds, namely, those of ethane, acetic 

 ester, malonic ester and acetoacetic ester. In this latter class the 

 explosive character of the triazo-group has been very prominent ; for 

 instance, whilst a drop of ethyl triazoacetate when thrown on a hot 

 plate merely inflames without detonation, 1 : 2-bistriazoethane explodes 

 with considerable violence ; and this property is particularly notice- 

 able when both triazo-groups are attached to the same atom of carbon, 

 1 : 1-bistriazoethane continuing in existence only a few minutes after 

 isolation, when it disappeared with a deafening explosion. Another 

 characteristic feature of these materials becomes evident when their 

 vapour is inhaled, the experience of pleasure in an ethereal odour 

 being quickly followed by a throbbing sensation at the base of the 



