Hydrogen Sulphide
H2S, sulphide of hydrogen, hydric sulphide, sulphydric acid, hydrosulphuric acid, sulphuretted hydrogen. A gas obtained by passing hydrogen through sulphur, or by burning sulphur vapor in hydrogen.
HYDROGRAPHY (hi-drog-rä-fē), a branch of science which deals with the measurement and description of the seas, lakes, rivers, and other waters, as used for purposes of commerce or navigation; the art of marine surveying and of the construction of charts.