We describe a vacuum-based pressure-detecting capillary viscometer for the viscosity determination
of Newtonian fluids without known density. The viscometer operates on the principle that the
variation in air pressure of the vacuum vessel ##IMG##
[http://ej.iop.org/images/0143-0807/36/6/065045/ejp520534ieqn1.gif] {$pleft(tright)$} replaces the
flow rate and pressure drop measurements which are usually required for the operation of a capillary
tube viscometer. The mathematical expression for ##IMG##
[http://ej.iop.org/images/0143-0807/36/6/065045/ejp520534ieqn2.gif] {$pleft(tright),$} found in
the terms of the Lambert-W function, is used to fit the experimental data for viscosity
determination. The results for viscosities of distilled water and 50 wt.% glycerol aqueous solution
obtained under ambient temperature condition were compared to reference data and a good agreement
was observed. The viscometer is suitable for undergraduate l…