[AS.] Water in the gaseous state. The clouds of vapor which are seen to issue from a kettle of boiling water are also popularly called " steam ; " but these white clouds consist chiefly of condensed steam, and do not possess the properties which belong to steam considered as a gas. Dry steam is as much invisible as atmospheric air. Owing to the great pressure which it exerts, to the large amount of heat which it can carry, and to the ease with which it can be condensed, steam has been found better fitted than any other gas for use in engines employed for the production of mechanical work.