Viscometer, Ostwald

Quick Answer: The Ostwald Viscometer is a U-shaped glass capillary instrument that determines the kinematic viscosity of Newtonian liquids by timing how long a fixed volume of sample takes to flow through a narrow calibrated capillary. It works on a completely different principle from LabEquip’s hydrometers, which read density by buoyancy rather than timing a flow.

Product Description

Unlike a hydrometer, which floats in a liquid to read density directly, an Ostwald Viscometer measures how resistant a liquid is to flow. The operator draws the sample up past a fill mark in one arm of the U-tube, then times how long it takes to drain back down past two calibration marks under gravity through the narrow capillary section. Flow time is proportional to kinematic viscosity, and comparing the flow time of a test liquid to that of a reference liquid of known viscosity gives the result.

What Makes This Instrument Distinct

This is a capillary-flow-time viscometer, not a hydrometer variant – it belongs to a different family of measuring instruments in LabEquip’s range. Where our hydrometers (specific gravity, Beaume, Brix, Sikes, density and alcoholometer scales) all use buoyancy to read density, the Ostwald Viscometer uses timed gravity flow through a fixed capillary to characterise a liquid’s resistance to flow. It is intended for Newtonian liquids, where viscosity does not change with flow rate or shear, and is commonly used in pharmaceutical, chemical and petrochemical quality control for fluid consistency testing.

Specifications

Care & Maintenance

• Clean thoroughly with an appropriate solvent and dry completely after each use; residue inside the fine capillary bore will distort flow-time readings.
• Store upright and protected from dust, and avoid any mechanical shock to the capillary section, which is the most fragile and precision-critical part of the instrument.
• Bring samples to a controlled, stable temperature before timing, since viscosity is strongly temperature-dependent.
• Periodically verify flow times against a reference liquid of known viscosity to confirm the capillary has not become partially blocked or worn.

Why Choose LabEquip

LabEquip supplies a broad range of physics and chemistry measuring instruments beyond hydrometers, including viscometers, for labs that need accurate fluid-property testing across different measurement principles. Explore related instruments:

• Hydrometer, Specific Gravity, Industry
• Alcoholometer
• Measuring Instruments Category

Frequently Asked Questions

What does an Ostwald Viscometer measure?
It measures the kinematic viscosity of a Newtonian liquid by timing how long a fixed sample volume takes to flow through a calibrated capillary under gravity.

How is this different from a hydrometer?
A hydrometer floats in a liquid to read density by buoyancy, while an Ostwald Viscometer times a gravity-driven flow to characterise resistance to flow (viscosity) – a different physical property measured by a different method.

Why does temperature matter for viscosity testing?
Viscosity is strongly temperature-dependent, so samples should be brought to a controlled, stable temperature before timing for a repeatable result.

What capillary bore or capacity does this viscometer have?
Exact capillary bore and capacity vary by grade and intended viscosity range; please confirm your requirement with our sales team.

Is this suitable for non-Newtonian liquids?
The Ostwald Viscometer is designed for Newtonian liquids, where viscosity does not vary with flow rate; please confirm your sample type with our sales team.

How should I clean this viscometer between tests?
Clean thoroughly with an appropriate solvent and dry completely, since any residue inside the fine capillary bore can distort flow-time readings.

Last Updated: September 2026