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PHYSICS AND CHEMISTRY. 455
DALTON were confirmed and extended by BERZELIUS, and
also by WOLLASTON, who introduced a classification by
equivalencies instead of that by atomic weights.
This subject received enlargement at the hands of GAY-
LuSSAC who recommended that in analyzing chemical
combinations attention should also be paid to the volumetric
relation of bodies when in the gaseous state. In 1805, he,
in conjunction with ALEXANDER VON HUMBOLDT, discovered
that water is composed of one volume of oxygen
and two volumes of hydrogen. Afterwards he examined
other combinations in the same way and established the
fact that their constituents in the gaseous state stand in
definite relations of volume to one another; he thus laid
the foundation of the theory of volumes. GAY-LUSSAC
published the valuable results of his labours upon the expansion
of gases by heat; upon the density of vapours, for
the determination of which he contrived peculiar methods
of investigation ; upon iodine (which had been discovered
shortly before) and its combinations, and also upon several
combinations of chlorine. He gave the first correct description
of the composition of hydrocyanic acid, explained
the nature of cyanogen, discovered hydriodic acid and
hyposulphuric acid and simplified the examination of many
bodies made use of in daily life
The quantitative analysis of chemical combinations
entered upon a new stage when it became known that
the electrical current decomposes them. NICHOLSON,
CARLISLE, CRUIKSHANK, BERZELIUS and HISINGER made
several interesting observations on this subject, and
HUMPHREY DAVY gave them a theoretical basis. He
pointed out that water is decomposed by means of the
electric current into oxygen and hydrogen, and salts into
acids and bases of which the former bodies in each case
are discharged at the positive, the latter at the negative
pole of the Voltaic battery ; he proved the decomposability
of several compounds, as for instance the fixed alkalies, the
alkaline earths, baryta, strontia, magnesia, lime, etc., and
gave it as his opinion that chemical and electrical effects