CHEMISTRY GLOSSARY

degree    →   stupanj

1. Degree is a unit of temperature on a specified scale. The temperatures of boiling and freezing water are: in the Fahrenheit system 212 and 32 degrees; in the Celsius system 100 and 0 (zero) degrees.

2. Degree is a unit of angular measure. A circle is divided into 360 degrees, represented by the symbol °. Degrees are each divided into 60 minutes. Each minute has 60 seconds. Symbols for degree, minute, and second for plane angle is placed after the numerical value and a no space between the numerical value and the unit symbol (α = 2°3'4").

3. In algebra, the degree of a polynomial is the highest power of the variable in the polynomial. For example, 4x³ + 3x² + x + 7 have degree 3.

deionised water    →   deionizirana voda

Deionised water is water from which ionic salts have been removed by ion-exchange. It is used for many purposes as an alternative to distilled water.

deoxyribonucleic acid    →   dezoksiribonukleinska kiselina

Deoxyribonucleic acid (DNA) is a nucleic acid with 2-deoxy-D-ribose as the sugar in its nucleotides. DNA contains encoded genetic information, specifically templates for the synthesis of all of an organism’s proteins and enzymes.

DNA was first identified in the 1869 by Swiss chemist Friedrich Miescher (1844-1895). In 1953, American biologist James Dewey Watson (1928-) and English physicist Francis Harry Compton Crick (1916–2004) had discovered that DNA occurs in the cell as a double helix, with two long strands of the molecule wound around each other, and further that the chemical structure of the molecule dictates that adenine (A) always aligns or pairs with thymine (T), and cytosine (C) always pairs with guanine (G). It is this base pairing that allows DNA in a cell to copy itself, and transfer its information to a new cell. The diameter of the helix is 2.0 nm and there is a residue on each chain every 0.34 nm in the z direction. The angle between each residue on the same strand is 36°, so that the structure repeats after 10 residues (3.4 nm) on each strand.

desiccant dryers    →   sredstva za sušenje

Desiccant dryers (air dryers) use nonconsumable chemicals such as silica gel or active alumina, and can remove almost all the moisture from compressed air by adsorbing moisture on its surface. The method of regeneration, the process of removing adsorbed water from the desiccant, is the primary distinguishing feature among the various types of desiccant dryers. There are three ways to regenerate a desiccant: with air, internal or external heaters, or a heat pump.

Dewar flask    →   Dewarova posuda

Dewar flask or vacuum bottle is a container for storing hot or cold substances. It consists of two flasks, one placed inside the other, with a vacuum between. The vacuum prevents the conduction of heat from one flask to the other. For greater efficiency the flasks are silvered to reflect heat. The substance to be kept hot or cold, e.g., liquid air, is contained in the inner flask. The flask is named after British chemist and physicist Sir James Dewar (1842-1923). Dewar invented the Dewar flask in 1892 to aid him in his work with liquid gases. The common thermos bottle is an adaptation of the Dewar flask.

diagenesis    →   dijageneza

Diagenesis is the process that turns sediments into sedimentary rocks. The lithification (literally turning into stone) of the sediments is usually accomplished by a cementing agent. How the weight of the overlying material increases the grains closer together, reducing pore space and eliminating some of the contained water. This water may carry mineral components in solution, and these constituents precipitate as new minerals in the pore spaces. This causes cementation, which will then start to bind the individual particles together. Further compaction and burial may cause recrystallization of the minerals to make the rock even harder.

dialysis    →   dijaliza

Dialysis is a method by which large molecules (such as starch or protein) and small molecules (such as glucose or amino acids) may be separated in a solution by selective diffusion through a semipermeable membrane. Through this kind of membrane dissolved particles pass and colloid dimension particles fall behind. For example, if a mixed solution of starch and glucose is placed in a closed container made of a semipermeable substance (such as cellophane), which is then immersed in a beaker of water, the smaller glucose molecules will pass trough the membrane into the water, while the starch molecules remain behind.

light scattering    →   raspršenje

Light scattering is a type of diffuse reflection. When light strikes a rough surface, small flat areas are almost comparable to the wavelength, so the light scatters.

light year    →   svjetlosna godina

Light year (ly) is a unit of distance used in astronomy, defined as the distance light travels in one year in a vacuum (ly = 9.46052973·10¹⁵ m).

lipids    →   lipidi

Lipids are a loosely defined term for substances of biological origin that are soluble in nonpolar solvents. They consist of saponifiable lipids, such as glycerides (fats and oils) and phospholipids, as well as nonsaponifiable lipids, principally steroids.