Simplified Chemistry

An analytical technique that can be used to detect most elements when present in a sample in milligram quantities (or less). In neutron activation analysis the sample is exposed to a flux of thermal neutrons in a nuclear reac­tor. Some of these neutrons are cap­tured by nuclides in the sample to form nuclides of the same atomic number but a …

A sewage and waste-water treatment. The sludge produced after primary treatment is pumped into aeration tanks, where it is continuously stirred and aerated, resulting in the formation of small aggregates of sus­pended colloidal organic matter called floe. Floe contains numerous slime-forming and nitrifying bac­teria, as well as protozoans, which decompose organic substances in the sludge. Agitation or air injection maintains …

A presumptive test for blood in which a small amount of acetone (propenal) is added to the bloodstain, followed by a drop of hy­drochloric acid. Haemoglobin pro­duces derivatives such as haematin and haemin, forming small charac­teristic crystals that can be identified under a microscope.

A photosynthetic pigment that traps light energy and channels it to chlorophyll a, the primary pigment, which initiates the reactions of photosynthesis. Accessory pigments include the carotene and chlorophyll b, c, and d. 

A flammable material used to start and spread a fire in cases of arson. Petrol and paraffin are the substances commonly used. Traces of accelerant are detectable by gas chromatography in forensic work.

A chemical reaction that involves bimolecular removal of an atom or ion from a molecule. An example is the abstraction of hydro­gen from methane by reaction with a radical: CH4 + X → H3C· + HX

A long vertical column used in industry for absorbing gases. The gas is introduced at the bottom of the column and the absorbing liquid, often water, passes in at the top and falls down against the countercurrent of gas. The towers are also known as scrubbers.

1. (in spectroscopy) The molar absorption coefficient (symbol ε ) is a quantity that characterizes the absorption of light (or any other type of electromagnetic radiation) as it passes through a sample of the absorbing material. It has the dimensions of 1/{concentration x length). e is de­pendent on the frequency of the inci­dent light; its highest value occurs where the …

A way of denoting the absolute structure of an optical isomer . Two conventions are in use: The D-L convention relates the structure of the molecule to some reference molecule. In the case of sugars and similar compounds, the dextrorotatory form of glyceraldehyde (HOCH2CH(OH)CHO , 2,3-dihydroxy­propanal) was used. The rule is as follows. Write the structure of this molecule down …

1. Not dependent on or relative to anything else, e.g. absolute zero. 2. Denoting a temperature measured on an absolute scale, a scale of temperature based on absolute zero. The usual absolute scale now is that of thermodynamic temperature; its unit, the kelvin, was formerly called the degree absolute (0A) and is the same size as the degree Celsius. In …