For a long time it has been known that water, the most common of all liquids, has physical properties which vary widely from those of most other liquids. The large quantity of heat required to melt a gram of ice, the still larger quantity required to convert a gram of water into vapor at the same temperature and the existenee of a tem-perat~lre of maximum density between the melting and the freezing points, mark water as departing from the usual rules of liquid comportment. Already the list of the anomalies presented by water is long and yet it is no uncommon occurrence to have it increased. For instance Hauser in the July number of Drude's Anualen for I9Ol shows that at 320 C., the viscosity of water is not changed by a pressure of 4oo atmospheres, while at other temperatures it is changed.
Within the last decade serious attempts, have been made to furnish an explanation of the irregularities of water. The idea that water molecules are not H20 simply but are aggregates of tkis group is advanced by Raoult * as a result of his experiments upon the molecular lowering of the freezing point of solutions, and probably expressions of this view could be found long before. When in 1891 Roentgen attacked" the problem he used this suggestion and succeeded in furnishing a qualitative explanation.]" He regards water as composed of molecules of two kinds, which he designates ice molecules and molecules of the second kind. Ordinary water is considered to be a