ument, which in various modifications has
come into extensive use--the grease-spot photometer. In 1852 he began to
carry out electrolytical decompositions by the aid of the battery. By means
of a very ingenious arrangement he obtained magnesium for the first time in
the metallic state, and studied its chemical and physical properties, among
other things demonstrating the brilliance and high actinic qualities of the
flame it gives when burnt in air. From 1855 to 1863 he published with
Roscoe a series of investigations on photochemical measurements, which W.
Ostwald has called the "classical example for all future researches in
physical chemistry." Perhaps the best known of the contrivances which the
world owes to him is the "Bunsen burner" which he devised in 1855 when a
simple means of burning ordinary coal gas with a hot smokeless flame was
required for the new laboratory at Heidelberg. Other appliances invented by
him were the ice-calorimeter (1870), the vapour calorimeter (1887), and the
filter pump (1868), which was worked out in the course of a research on the
separation of the platinum metals. Mention must also be made of another
piece of work of a rather different character. Travelling was one of his
favourite relaxations, and in 1846 he paid a visit to Iceland. There he
investigated the phenomena of the geysers, the composition of the gases
coming off from the fumaroles, their action on the rocks with which they
came into contact, &c., and on his observations was founded a noteworthy
contribution to geological theory. But the most far-reaching of his
achievements was the elaboration, about 1859, jointly with G.R. Kirchhoff,
of spectrum analysis, which has put a new weapon of extraordinary power
into the hands both of chemists and astronomers. It led Bunsen himself
almost immediately to the isolation of two new elements of the alkali
group, caesium and rubidium. Having noticed some unknown lines in the
spectra of certain salts he was examining, he set to work to obtain the
substance or substances to which these were due. To this end he evaporated
large quantities of the Duerkheim mineral water, and it says much both for
his perseverance and powers of manipulation that he dealt with 40 tons of
the water to get about 17 grammes of the mixed chlorides of the two
substances, and that with about one-third of that quantity of caesium
chloride was able to prepare the most important compounds of the element
and determine th