A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robin Stuart
Date: 2020 Jul 28, 05:55 -0700
With the discussion of mercury artificial horizons (AH), I wondered whether gallium had been considered as a substitute. It has low toxicity and melts at 30°C. At under half the density of mercury, you need to purchase less than half the weight to get the same volume for the AH.
Searching Navlist shows that a gallium alloy was suggested for this purpose by George Huxtable in 2002. http://fer3.com/arc/m2.aspx/Liquid-metals-for-artificial-horizons-Huxtable-apr-2002-w6154. There is also research on the web on gallium for spinning parabolic mirrors http://adsabs.harvard.edu/full/1997PASP..109..319B
Although gallium will solidify nominally at 30°C it apparently has a tendency to supercool and remain liquid below that temperature. The eutectic alloy George mentions has a melting point of -19°C. Even if the gallium were to solidify, I wonder whether it would retain its level and surface reflectivity.
Another and perhaps the most important consideration is that having chunk of metal that melts with the heat of your hand sounds like a lot of fun!