Organic materials, substances

Principle. A known weight of the substance is heated with fuming nitric acid and silver nitrate in a sealed tube. The organic material is thus oxidised to carbon dioxide and water, whilst the halogen is converted quantitatively into the corresponding silver halide. The latter js subsequently washed out of the tube, filtered and weighed. 

Hydrophobic substances are soluble in nonpolar solvents, whereas their solubiUty in water is very limited. Many of these substances are also soluble in fats and Hpids and are also called hpophile compounds. Such substances have a tendency to avoid contact with water and to associate with a nonpolar, nonaqueous environment, such as a surface, eg, an organic particle, a particle containing organic material, or the lipid-containing biomass of an organism. 

Concentrated hydrochloric acid will dissolve many metals (generally those situated above hydrogen in the electrochemical series), as well as many metallic oxides. Hot concentrated nitric acid dissolves most metals, but antimony, tin and tungsten are converted to slightly soluble acids thus providing a separation of these elements from other components of alloys. Hot concentrated sulphuric acid dissolves many substances and many organic materials are charred and then oxidised by this treatment. 

In cases where it proves impossible to find a suitable indicator (and this will occur when dealing with strongly coloured solutions) then titration may be possible by an electrometric method such as conductimetric, potentiometric or amperometric titration see Chapters 13-16. In some instances, spectrophotometric titration (Chapter 17) may be feasible. It should also be noted that ifit is possible to work in a non-aqueous solution rather than in water, then acidic and basic properties may be altered according to the solvent chosen, and titrations which are difficult in aqueous solution may then become easy to perform. This procedure is widely used for the analysis of organic materials but is of very limited application with inorganic substances and is discussed in Sections 10.19-10.21. 

Nitric Acid and Organic Substances. Mixts of perchloric and nitric ac are frequently used to digest (render w sol) organic materials such as animal and vegetable oils, milk, homogenized animal tissues, etc. If the mixts are heated too... 

Isotopes are also used to determine properties of the environment. Just as carbon-14 is used to date organic materials, geologists can determine the age of very old substances such as rocks by measuring the abundance in rocks of radioisotopes with longer half-lives. Uranium-238 (t1/2 = 4.5 Ga, 1 Ga = 10y years) and potassium-40 (t,/2 = 1.26 Ga) are used to date very old rocks. For example, potassium-40 decays by electron capture to form argon-40. The rock is placed under vacuum and crushed, and a mass spectrometer is used to measure the amount of argon gas that escapes. This technique was used to determine the age of rocks collected on the surface of the Moon they were found to be 3.5-4.0 billion years old, about the same age as the Earth. 

The materials that accumulate to form sedimentary rocks are (i) products of disintegration (weathering) of rocks, (ii) volcanic ejecta, (iii) insoluble decomposition products, (iv) precipitated substances from aqueous solutions, and (iv) bio-organically derived substances. 

Except for dry incineration in a platinum crucible, oxygen-induced decomposition requires special apparatus in order to avoid the loss of volatile substances. Combustion of organic materials may be achieved with the... 

Antistatic agents are ionic substances, such as inorganic salts or organic materials, which attract water molecules. Outstanding materials are derived from the fatty amide and amine chemistry, such as ethoxylated alkyl amines, glycerolmonostearate, fatty alkanolamines, and sodium alkylsulfonates (C12-C16 alkyl groups are preferred because of low loss by evaporation). 

The Babylonians and Assyrians cemented stone slabs as well as bricks with bitumen (which is sometimes also referred to as asphalt), a mixture of a black or brown natural organic material with a pitchy luster and comminuted mineral. Bitumen is a thermoplastic solid material when heated above 50°C, it softens and becomes a thick, viscous liquid that reverts to a solid on cooling. It is composed of a natural mixture of hydrocarbons (organic substances composed of carbon, hydrogen, and oxygen) that occurs in natural... 

This section details the mass specta of reference molecular constituents and of various substances including waxes and vegetable oils that were recently investigated in order to establish comprehensive correlation between the mass spectra obtained on archaeological and museum samples and the main organic materials involved in their composition. 

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