hydrometer
noun [ C ] chemistry specialized uk/haɪˈdrɒm.ɪ.tər/ us/haɪˈdrɑː.mə.t̬ɚ/
液体比重计，浮秤（用于测量溶液密度的仪器，尤指封闭的长试管，一端有砝码，可使液体竖直流动）
a piece of equipment used to measure the density (= amount of matter in a particular quantity) of liquids, especially a long glass tube, closed and with a weight at one end so that it floats vertically