CHEMISTRY GLOSSARY

mustard agent    →   plikavac

Mustard agents are usually classified as blistering agents owing to the similarity of the wounds caused by these substances resembling burns and blisters. However, since mustard agents also cause severe damage to the eyes, respiratory system and internal organs, they should preferably be described as blistering and tissue-injuring agents. Normal mustard agent (yperite), 1,1-thio-bis-[2-chloroethane], reacts with a large number of biological molecules. The effect of mustard agent is delayed and the first symptoms do not occur between 2-24 hours after exposure. At room temperature, mustard agent is a liquid with low volatility and is very stable during storage.

nerve poison    →   živčani bojni otrov

Nerve poison (nerve gas, agents) have had an entirely dominant role since the Second World War. Nerve poisons acquired their name because they affect the transmission of nerve impulses in the nervous system. All nerve poisons belong chemically to the group of organo-phosphorus compounds. They are stable and easily dispersed, highly toxic and have rapid effects both when absorbed through the skin and via respiration. Nerve poisons can be manufactured by means of fairly simple chemical techniques. The raw materials are inexpensive and generally readily available.

The most important nerve agents included in modern chemical weapons arsenals are:

Nerve poisons are colorless, odorless, tasteless liquids of low volatility. Antidotes are atropine sulfate and pralidoxime iodide.

Ostwald’s viscometer    →   Ostwaldov viskozimetar

Ostwald viscometer, also known as U-tube viscometer or capillary viscometer is a device used to measure the viscosity of the liquid with a known density. The method of determining viscosity with this instrument consists of measuring the time for a known volume of the liquid (the volume contained between the marks A and B) to flow through the capillary under the influence of gravity. Ostwald viscometers named after the German chemist Wilhelm Ostwald (1853-1932).

The instrument must first be calibrated with materials of known viscosity such as pure (deionized) water. Knowing the value of viscosity of one liquid, one can calculate the viscosity of other liquid.

where η₁ and η₂ are viscosity coefficients of the liquid and water, and ρ₁ and ρ₂ are the densities of liquid and water, respectively.

parallax    →   paralaksa

Parallax is a deceptive change of the position of an object which is observed while the position of the observer changes. Position of eye at all volumetric vessels must be at the same level as the meniscus. If not, the parallax will cause an error while reading the position of the meniscus of a liquid in a burette. It will be a positive mistake if the eye is lower, and negative if the eye is higher than the meniscus plane.

petroleum    →   nafta

Petroleum (crude oil) is a dark viscous liquid usually found under Earth’s surface or sea bottom. It is a very complex mixture of different compounds, mostly of hydrocarbonates of alkane, cycloalkane and aromatic sort whose composition is variable from oil field to oil field.

picnometer    →   piknometar

Picnometer is a special glass flask which is used for determining a relative density of liquids using the weight of a known volume. It usually has a glass faceted cork which is pierced in the centre like a thin capillary through which surplus of liquid runs out.

pipette    →   pipeta

Pipettes are glass tubes which are tapers towards at both ends into narrow opened tubes. According to their design two types of pipettes can be distinguished:

Volumetric pipettes

Volumetric pipettes (transfer or belly pipette) are used in volumetric analysis, when there is a need for taking exact smaller volume of a sample solution or reagent. The upper tube of volumetric pipette has a ringlike marking (mark) which marks its calibrated volume. Pipettes calibrated to deliver (TD or Ex) the indicated volume. By sucking in (with mouth, propipette or a water pump) the liquid is pulled in a little bit above the mark and the opening of the pipet is closed with a forefingertip. Outer wall of pipet is wiped and, with a slight forefinger loosening, the liquid is released until it reaches the mark. Mark must figure as a tangent on a lower edge of the liquid meniscus. A pipette is emptied out by lifting the forefinger off and letting the liquid flow out of the pipette freely. After another 15 s and the tip of the pipette is pulled onto the inner wall of the vessel. It is absolutely forbidden to blow out the contents of the pipette

Graduated pipettes

Graduated pipettes (Mohr pipette) have a scale divided into units of one and of 1/10th of a millilitre. Because of their wide necks it is less accurate than the volumetric pipette. They are used when taking volume of solutions in which accuracy does not have to be very high. They are filled in the same way as volumetric ones and liquid can be gradually released.

reflux condenser    →   povratno hladilo

Reflux condenser is used for repeated transformation of vapour in liquid in order to prevent the loss due to evaporation.

saturated solution    →   zasićena otopina

Saturated solution is a solution that holds the maximum possible amount of dissolved material. When saturated, the rate of dissolving solid and that of recrystallisation solid are the same, and a condition of equilibrium is reached. The amount of material in solution varies with temperature; cold solutions can hold less dissolved solid material than hot solutions. Gases are more soluble in cold liquids than in hot liquids.

Schellbach’s burette    →   Schellbachova bireta

When colourless liquids are used, parallax mistake is avoided by use of Schellbach’s burette. On the inside wall opposite to graduation scale it has a melted in ribbon from milky glass in the middle of which a blue line is found. The level of liquid is now spotted very easily because of light breaking in the meniscus blue line now looks like a double spike.