that these somewhat intricate and difficult investigations were brought to a successful close."
Perhaps none of his labors are more distinguished than the experiments with which he and Kirchhoff laid the foundation of the new science of spectrum analysis. Among his own most important transactions in this work was the discovery, by means of the spectrum lines, of the metals cæsium and rubidium. He first saw the cæsium lines, says Professor Roscoe, in a few milligrammes of the alkaline residue obtained in an analysis of the Dürkheim mineral waters, and the discovery of a second new metal (rubidium) soon followed that of the first. "So certain was he of the truth of his spectroscopic test, that he at once set to work to evaporate forty tons of the water, and with 16·5 grammes of the mixed chlorides of the two new metals which he thus obtained he separated the one metal from the other (no easy task) and worked out completely their chemical relationship and analogies; so much so, that the labors of subsequent experimenters have done little more than confirm and extend his observations." Another research in this direction was that on the spark spectra of the metals contained in cerite and other rare minerals, which he carefully mapped in such a manner as to make the separation and identification possible.
Bunsen's name is identified with two instruments which he has devised, which have come into general use in science and the arts; the Bunsen gas-burner, which is almost indispensable in laboratories and in many processes of manufacturing, and is used in many households; and the Bunsen pump for accelerating filtration, which those who employ it could likewise hardly do without.
His published writings are many. Most of them are special papers relating to the subjects of investigation that have been already mentioned; others embody more general results of his studies. His visit to Iceland gave rise to several papers on the various physical, geological, and volcanic phenomena of the island; his studies in metals to a number of monographs; his spectroscopic studies to "Chemical Analysis based on Observations of the Spectrum," published by him and Kirchhoff. Besides these, we may mention "Researches on Chemical Affinity"; "On a New Volumetric Method"; and "A Treatise on Gas Analysis."
Concluding his notice in "Nature," from which we have drawn liberally in the preparation of this article. Professor Roscoe says: "The many hundreds of pupils who, during the last half-century, have been benefited by personal contact with Bunsen will all agree that as a teacher he is-without an equal. Those who enjoy his private friendship regard him with still warmer feelings of affectionate reverence. All feel that to have known Bunsen is to have known one of the truest and noblest-hearted of men."