Thomas Andrews Discovered Critical Temperatures of Gases | Developed Concepts of Critical Temperature and Critical Pressure

Thomas Andrews – discoverer of critical temperatures of gases

Article On Thomas Andrews

Biography & contributions

Thomas Andrews was an Irish chemist and physicist born on December 19, 1813 – died on November 26, 1885. Andrews established the various important concepts of critical temperature and pressure. He showed that a gas will pass into the liquid state and also proved that ozone is a form of oxygen.

He worked on phase transitions between gases and liquids. In 1860 Andrews developed concepts of critical temperature and critical pressure. Andrews reputation mainly rests on his work with liquefaction of gases. In the 1860s he carried out a very complete inquiry into the gas laws-expressing the relations of pressure, temperature, and volume in carbon dioxide.

Andrews' experiments on phase transitions, he showed that carbon dioxide may be carried from any of the states we usually call liquid to any of those we usually call gas, without losing homogeneity.

Phase transitions

A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another one by heat transfer. The term is most commonly used to describe transitions between solid, liquid and gaseous states of matter, and, in rare cases, plasma. During a phase transition of a given medium certain properties of the medium change, often discontinuously, as a result of the change of some external condition, such as temperature, pressure. Phase transitions occur when the thermodynamic free energy of a system is non-analytic for some choice of thermodynamic variables. It is sometimes possible to change the state of a system diabatically in such a way that it can be brought past a phase transition point without undergoing a phase transition.

Liquefaction process

Liquefaction is an important process commercially because substances in the liquid state take up much less room than they do in their gaseous state. Liquefaction is also used in commercial and industrial settings to refer to mechanical dissolution of a solid by mixing, grinding or blending with a liquid.


Ozone, the first allotrope of any chemical element to be recognized, was proposed as a distinct chemical substance by Christian Friedrich Schonbein in 1840. Ozone is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen. Ozone is formed from dioxygen by the action of ultraviolet light and also atmospheric electrical discharges, and is present in low concentrations throughout the Earth's atmosphere. In total, ozone makes up only 0.6 ppm of the atmosphere. It is therefore used commercially only in low concentrations.

Ozone is a powerful oxidant and has many industrial and consumer applications related to oxidation. Ozone is colorless or slightly bluish gas (blue when liquefied), slightly soluble in water and much more soluble in inert non-polar solvents such as carbon tetrachloride or fluorocarbons, where it forms a blue solution. Ozone is a powerful oxidizing agent, far stronger than O2. It is also unstable at high concentrations, decaying to ordinary diatomic oxygen.

It has a varying half-life length, depending upon atmospheric conditions. In the laboratory, ozone can be produced by electrolysis using a 9 volt battery, a pencil graphite rod cathode, a platinum wire anode and a 3 molar sulfuric acid electrolyte. Ozone is used as an alternative to chlorine or chlorine dioxide in the bleaching of wood pulp. It is often used in conjunction with oxygen and hydrogen peroxide to eliminate the need for chlorine-containing compounds in the manufacture of high-quality, white paper.

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