Glass U Tube For Manometers And Electrolysis

U Tube

Uniform Bore Geometry: Manufactured with a consistent internal diameter throughout the radius to prevent hydrostatic anomalies, ensuring precise differential pressure readings and unobstructed gas flow during absorption processes.

Precision-Annealed Borosilicate 3.3: Fabricated from low-expansion Type 1 glass that undergoes computer-controlled thermal stress relief, providing exceptional resistance to thermal shock and corrosive reagents encountered in exothermic chemical reactions.

$5.08

Quick Answer: A glass U tube is a length of glass tubing bent into a U shape with two open, upright limbs. It serves as a simple manometer, a drying or absorption tube, a salt bridge in electrochemical cells and a small cell for electrolysis demonstrations.

One Shape, Several Experiments

Because both limbs are open and join at the bottom, liquid in a U tube settles at the same height on each side when the pressures above are equal. Connect one limb to a gas supply or a flask and the levels separate; the difference in height, read against a scale, measures the pressure difference. This is the simple manometer used in physics lessons on pressure and in chemistry set-ups to watch pressure change during a reaction.

Packed with granules of anhydrous calcium chloride and closed with bored bungs, the tube becomes a drying tube through which a gas passes on its way to a collecting vessel; packed with soda lime, it absorbs carbon dioxide. Filled with potassium chloride or potassium nitrate solution set in agar, it forms the salt bridge between the two half-cells of a Daniell cell. And with an electrode in each limb, it keeps the products of electrolysis apart, such as the brown iodine at the anode and the alkaline region at the cathode when potassium iodide solution is electrolysed with a little indicator.

The title names a plain U tube; versions with side arms or stopcocks are separate designs. Limb length, bore and glass type are not stated. In gas purification trains, a gas washing bottle handles liquid absorbents while the U tube holds solids.

Applications

Simple water or oil manometer for measuring small gas pressure differences
Drying a gas with calcium chloride granules before collection
Salt bridge linking zinc and copper half-cells in a Daniell cell practical
Electrolysis of potassium iodide or copper(II) sulfate solution with the products kept apart in each limb
Comparing the densities of two immiscible liquids by balancing their columns

Specifications

Form	Glass tube bent into a U with two open limbs
Uses	Manometer, drying or absorption tube, salt bridge, electrolysis cell
Closures	Bored rubber bungs in each limb as needed
Side arms	None named in the title
Limb length, bore and glass type	Confirm at enquiry

Care & Handling

Clamp the tube by one limb to a stand; it is not free-standing.
Pack drying agents loosely, with a plug of cotton wool at each end, so gas can pass without blowing granules out.
Clear salt-bridge agar while it is still soft by standing the tube in hot water.
When fitting bungs, grip the limb close to the rubber rather than at the bend, which is the weakest point.

Why Choose LabEquip

Schools and colleges use U tubes across physics and chemistry, so they are often bought in class sets and shared between departments. You can order this item from LabEquip’s chemistry lab equipment range; send limb length and quantity through the contact page.

Frequently Asked Questions

How does a U tube manometer measure pressure?

The liquid levels in the two limbs are equal when the pressure above each is the same. When one side is connected to a gas at higher pressure, the liquid is pushed down on that side; the height difference multiplied by the liquid density and g gives the pressure difference.

What liquid should I use in a U tube manometer?

Coloured water suits small pressure differences and is easy to read. A denser liquid gives a smaller height difference for the same pressure, so it suits larger differences; mercury is avoided in schools because of its toxicity.

How do I make a salt bridge in a U tube?

Dissolve agar in hot potassium chloride or potassium nitrate solution, pour it into the tube while hot, and let it set. The gel carries ions between the half-cells while stopping the two solutions from mixing.

Why electrolyse in a U tube instead of a beaker?

The two limbs keep the products at each electrode apart, so they can be seen and tested separately, for example iodine at the anode and alkali at the cathode when potassium iodide solution is electrolysed.

Can I use the U tube as a drying tube?

Yes. Fill it with granules of a drying agent such as anhydrous calcium chloride, hold them in with cotton wool plugs, and fit bored bungs with tubes to each limb. Check that the drying agent does not react with the gas, as calcium chloride does with ammonia.

Does this U tube have side arms?

The title describes a plain U tube, which has no side arms. U tubes with side tubes near the top of each limb are a different pattern, often used as drying tubes; mention that pattern when you enquire if it is the one you need.

Last Updated: September 2026