Spirit is considered as suitable liquid for leveling devices, Why?

A spirit level is a device used to check whether plane or surface is perfectly vertical or horizontal.
it commonly used for applications likes construction works, installation of machines and instruments on workshop floor also for photography and videography.

Ever wondered which liquid contained inside the glass? Yes, its Spirit. but ever thought why spirit?

let's think about water. filling a tube with water will work the same as spirit, but problems are associated with the physical properties of water. whenever we use spirit level working at extreme weather conditions like low temperature, water will freeze and tube with frozen water is none of the use.

Second liquid might be ethanol. ethanol works well. if accidentally tube bursts and ethanol flows out it is harmful for the user. because ethanol is hazardous for the human.

So after all explanation spirit is probably the best suggestion. on the other hand, the spirit is safe to use. even if accidentally comes in contact with skin it's not that much harmful.