CHEMISTRY GLOSSARY

Liebig condenser    →   Liebigovo hladilo

Liebig condenser is used for condensing of vapours that pass trough the centre tube. It is cooled with water that passes in the outer tube (shell around the centre tube) in the opposite direction than the one of hot vapour. Though named after the German chemist Justus von Liebig (1803-1873), he cannot be given credit for having invented it because it had already been in use for some time before him.

Contat-Gockel’s valve    →   Contat-Gockelov ventil

Contat-Göckel’s valve is used for maintenance of inert atmosphere in a flask. The valve is filled with a saturated solution of sodium bicarbonate (NaHCO₃) so that the end of the tube is covered. Solution inside the valve keeps the flask contents away from the oxygen influence from air. If low pressure is created inside the flask (when the flask is cooled), the solution will penetrate inside it from funnel and in a reaction with acid CO₂ is generated which fills up the flask.

Solution from the funnel will keep penetrating until CO₂ pressure in the flask is equalised with the outer pressure.

convection    →   konvekcija

Convection is the process by which heat is transferred from one part of a fluid to another by movement of the fluid itself. There are two methods by which this can be carried out.

Natural convection, in which movement occurs as a result of gravity. Heat transferred through a fluid medium, such as air or water, by currents that result from the rising of less dense, warm fluid and the sinking of heavier, cooler fluid.

Forced convection is where hot fluid is transferred from one region to another by a mechanical means (fans or pumps).

gas liquefying    →   ukapljivanje plinova

In order to achieve transition of a gas into liquid state it is necessary to lower its temperature, or decrease its volume, or increase its pressure. Above the critical temperature it is impossible to liquefy a gas. When liquefying a gas by Linde’s procedure, dampening or Joule-Thomson’s effect is used. First, the compressed air from the compressor is cooled with cooling water, the cooled air expands at a lower pressure in the dampening valve at which it cooled. The cooled air now returns to the compressor, cooling down the expanding air. By repeating this process the air is cooled enough to transit to the liquid state.

melting point    →   talište

Melting point is the temperature at which a solid becomes a liquid at normal atmospheric pressure.

A more specific definition of melting point (or freezing point) is the temperature at which the solid and liquid phases of a substance are in equilibrium at a specified pressure (normally taken to be atmospheric unless stated otherwise). A pure substance under standard condition of pressure has a single reproducible melting point. The terms melting point and freezing point are often used interchangeably, depending on whether the substance is being heated or cooled.

superfluid helium    →   superfluidni helij

Superfluidity in helium-4 was discovered in 1938 by the Soviet physicist Pyotr Leonidovich Kapitsa. Helium-4 exhibits superfluidity when it is cooled below 2.18 K (-270.97 C), which is called the lambda (λ) point. At these temperatures, helium-4 exhibits the characteristics of two distinct fluids, one of which appears to flow without friction. An extensive series of experiments showed that in this state of helium, called helium II (He II), there is an apparent enormous rise in heat conductivity, at an increase rate of about three million. Another unusual property of He II is its mobile, rapid flow through capillaries or over the rim of its containment vessel as a thin film that exhibits no measurable viscosity and appears unaffected by the forces of gravity or evaporation and condensation.