#hydrometer__gravimeter  a measuring instrument for determining the specific gravity of a liquid or solid
  supertype:  measuring_instrument__measuringinstrument__measuring_system__measuringsystem__measuring_device__measuringdevice  instrument that shows the extent or amount or quantity or degree of something
  subtype:  salinometer  a hydrometer that determines the concentration of salt solutions by measuring their density
  subtype:  thermohydrometer__thermogravimeter  a hydrometer that includes a thermometer

No statement uses or specializes hydrometer; click here to add one.