48 Obituary Notices of Fellows deceased. 



determined to make a gas lamp for laboratory use in which a mixture 

 of gas and air should burn without smoke or explosion in a simple 

 tube. His clear conception of the laws which apply to the inflamma- 

 tion of such a 'mixture showed him that it was possible, although no 

 one had hitherto succeeded in doing it, so to arrange the dimensions 

 that a steady, non-luminous, but highly heated flame could be obtained 

 without danger of the mixed gases becoming explosive within the 

 tube. This result, apparently simple enough, was however only 

 reached after a long series of delicate experiments. And now this 

 burner is not only a necessity in every laboratory, but in every house- 

 hold, and in every manufactory where a clean flame is wanted. Next 

 in importance come a series of investigation on various branches of 

 analytical work, all characterised by original methods and delicate 

 manipulative skill. Of these his iodometric method now in general 

 use, and his elaborate and classical methods of silicate and mineral 

 water analysis, are perhaps the most prominent. 



Amongst the work done in conjunction with his pupils, the best 

 known are the long series of researches on photochemical measure- 

 ments with Roscoe, and that on the electrolytic preparation of the 

 metals of the alkali-earths with Matthiessen. 



In the early sixties, his crowning investigation on spectrum analysis 

 made its appearance, including the work done, together with his col- 

 league Kirchhoff, which gave rise to the discovery of ca3sium and 

 rubidium. Up to 1875 he continued to work at this favourite subject, 

 on which he published many memoirs, especially remarkable being that 

 on the absorption spectra of the compounds of the metals of the rare 

 earths. Amongst these is to be found the first observation of the high 

 luminosity caused by the ignition in the colourless flame of certain of 

 these earths, a fact which has since become of immense commercial 

 value in incandescent gas-burners. 



His research on caesium and rubidium and their salts is, perhaps, the 

 one in which his marvellous power of exact experimentation is seen to 

 the greatest advantage. From 44,000 kilos of the Dtirkheim water 

 he obtained only 16 grammes of the mixed chlorides. After he had 

 separated these by a long and elaborate series of processes, only about 

 5 grammes of the chemically pure caesium salt remained. With this 

 comparatively minute quantity, Bunsen succeeded not only in preparing 

 and analysing all the more important compounds of the metal, but in 

 ascertaining by accurate goniometrical measurements their crystalline 

 forms. So that we thus became acquainted with the properties and 

 relationships of the compounds of this rare new metal as we had long 

 been with those of potassium and sodium. But his labours at this 

 time were not confined to one branch of the science. His researches 

 covered a wide field, and were of the most diverse character, always, 

 however, distinguished by the same seeking after exactitude both as 



