CHEMISTRY GLOSSARY

Brinell hardness    →   Brinellova tvrdoća

Brinell hardness is a scale for measuring the hardness of metals introduced around 1900 by Swedish metallurgist Johan Brinell (1849-1925). A small chromium steel ball is pressed into the surface of the metal by a load of known weight. The loading force is in the range of 300 N to 30 000 N. The ratio of the mass of the load in kilograms to the area of the depression formed in square millimetres is the Brinell Hardness Number.

precision balance    →   tehnička vaga

Precision balances typically display results from three to one decimal places (0.001 g up to 0.1 g). The readability precision balances are reduced when compared to analytical balances but, precision balances accommodate higher capacities (up to several kilograms). In its traditional form, it consists of a pivoted horizontal lever of equal length arms, called the beam, with a weighing pan, also called scale, suspended from each arm.

In electronic top pan, or toploader balances, mass is determined not by mechanical deflection but by electronically controlled compensation of an electric force. The signal generated enables the mass to be read from a digital display. The mass of the empty container can be stored in the balance’s computer memory and automatically deducted from the mass of the container plus its contents.

absolute temperature    →   apsolutna temperatura

Absolute temperature denoting a temperature measured on the absolute scale, a scale of temperature based on absolute zero as the lowest temperature.

antioxidant    →   antioksidans

Antioxidants are compounds that slow down oxidation processes that degrade foods, fuels, rubber, plastic, and other materials. Antioxidants like butylated hydroxyanisole (BHA), are added to food to prevent fats from becoming rancid and to minimize decomposition of vitamins and essential fatty acids; they work by scavenging destructive free radicals from the food.

arsenic    →   arsen

Arsenic was discovered by Albertus Magnus (Germany) in 1250. The origin of the name comes from the Greek word arsenikon meaning yellow orpiment. It is steel-grey, brittle semi-metal. Resists water, acids and alkalis. Tarnishes in air, burns in oxygen. Highly toxic by inhalation or ingestion. Arsenic is found in mispickel (arsenopyrite). Many of its compounds are deadly poison and used as weed killer and rat poison. Used in semiconductors. Some compounds, called arsenides, are used in the manufacture of paints, wallpapers and ceramics.

atmosphere    →   atmosfera

1. Atmosphere is the column of air which is extending several hundred kilometers above the surface the Earth's surface. The density of this air decreases as you proceed up from the surface. The air in the atmosphere consists of 78 % nitrogen, 21 % oxygen, and 0.9 % argon. The remaining 0.1 % of the atmosphere consists of ozone, water vapor, carbon dioxide, methane, helium, and neon. The atmosphere is divided into different regions. The lowest two layers are the troposphere (the layer closest to the earth) and the stratosphere respectively. These two layers contain more than 99 % of the atmospheric molecules.

2. Standard atmosphere (atm) is an obsolete pressure and stress unit which should be discontinued. It is unit of pressure equal to the air pressure measured at mean sea level.

1 atm = 101 325 Pa

Technical atmosphere (at) is an obsolete MKpS pressure and sttress derived unit.

1 at = 98 066.5 Pa

1 atm = 1.033 227 453 at

calorific value    →   kalorična vrijednost

Calorific value is the heat produced by a given weight of fuel on the completion of combustion; it is measured in kilojoules per kilogram (kJ/kg).

gray    →   grej

Gray (Gy) is the SI derived unit of absorbed dose of radiation. The gray is the absorbed dose when the energy per unit mass imparted to matter by ionising radiation is one joule per kilogram (Gy = J/kg). The unit was named after the British scientist Louis Harold Gray (1905-1965).

Haber, Fritz    →   Haber, Fritz

Fritz Haber (1868-1934) is German physical chemist, winner of the Nobel Prize for Chemistry (1918) for his development of a method of synthesizing ammonia. With Carl Bosch, he invented a process for the large-scale production of ammonia for use in nitrogen fertilizer.

herbicide    →   herbicid

Herbicide is any chemical compound used to kill pests that destroy agricultural production. Pesticide include herbicides (such as 2.4 D and Paraquat), which kill unwanted plants or weeds.