In a glass thermometer, the liquid alloy of which metal moistens the inner surface of the glass?
The gallium (Ga) does not occur as a free element in nature but as Ga-III compounds. The element Ga is a liquid at temperatures greater than 29.76 C (85.57 F).
Since its discovery in 1875, Ga is used to make alloys with low melting points (<<29.76 C). Hence, gallium alloys are used in thermometers as a non-toxic and alternative to mercury which can withstand higher temperatures than mercury. It is then claimed for the liquid alloy 'galistan', an even lower melting point of -19 C (-2 F), well below the freezing of water. The 'galistan' is brand-name and a common name for a liquid Ga-alloy whose composition is part of a family of eutectic alloys. The eutectic system is a homogeneous mixture of substances that melts or solidifies at a single temperature, which is the lowest possible melting temperature over all of the involved component species. The galistan is composed of 68.5% gallium, 21.5% Indium, and 10.0% tin by weight.
While using 'galistan' in a glass thermometer, the inner tube surface must be coated with gallium (III) oxide (Ga2O3) to prevent the alloy from wetting the glass surface.