Water colored by the indicator methylorange squirts into the flask filled with hydrogen chloride gas (a colourless gas with a pungent odour). While it dissolves in water, $HCl$ leaves a vacuum which is replaced by the water fountain. The methylorange turns to red, an acid has formed.
The solution of hydrogen chloride gas in water is called chlorhydric acid
Chlorhydric acid is a colourless liquid, highly corrosive and with a pungent odour