Question

Why can't we use any other liqiud other than mercury in a barrowmeter

Answer 1

mercury has a good linear expansion on temp scale[i.e the same amount of expansion per degree],whereas lot of other liquids have exponential expansion curves over large scales[i.e differing amount of expansion per degree change].this means it is easier to have an equal scale with mercury rather than other liquids where the scale have to be non-linear

Answer 2

because it is highly expandable  it s opaque and shining