The hydrometer assembly comprises telescoping tubes of which the inner one is transparent or has a windowed area. In the fully telescoped state of the two tubes, clamping parts associated with them retain the hydrometer float in a locked position within the inner tube. The closure for the lower extremity of the outer tube includes a fine mesh screen so that extending of the tubes longitudinally permits a liquid which is to be evaluated to be drawn into and retained within the tube interior. The extension of the tubes also releases the hydrometer float which then rises in the in-drawn liquid to a level at which its scaled part can be read through the windowed part of the inner tube.
