the world > matter > constitution of matter > oiliness or greasiness > [noun] > oiliness > contrivance for testing or measuring (4)
An instrument for determining the density, and so the purity, of oils.
a test carried out using oil, or for ascertaining some property of oil, such as its flashpoint, lubricating quality, or edibility.
a device for performing a test on an oil.
A hydrometer for measuring the relative density of oils (and hence their purity).