Synthetic substance

Trace Mercury. There are a number and variety of methods and instmments to determine trace quantities of both inorganic and organic mercury ia natural or synthetic substances (19) (see also Trace and residue analysis). Literature describiag numerous techniques and trace element analysis of a myriad of mercury-containing substances is available (20). Only the most commonly used methods are mentioned hereia. 

Research conducted durkig and subsequent to the 1970s revealed that vitamin D is better defined as those natural or synthetic substances that ate converted by animals kito metaboUtes that control calcium and phosphoms homeostasis and act ki a variety of other hormonal-like functions. 

Trichloroethylene [79-01-6J, trichloroethene, CHCL=CCL2, commonly called "tri," is a colorless, sweet smelling (chloroformlike odor), volatile Hquid and a powerhil solvent for a large number of natural and synthetic substances. It is nonflammable under conditions of recommended use. In the absence of stabilizers, it is slowly decomposed (autoxidized) by air. The oxidation products are acidic and corrosive. Stabilizers are added to all commercial grades. Trichloroethylene is moderately toxic and has narcotic properties. 

Persistent synthetic substances which may float, remain in suspension or sink and interfere with any use of the waters... 

Studies on Drug Addiction, with special reference to Chemical Structure of Opium Derivatives and Allied Synthetic Substances and their Physiological Action, by Small, Eddy, Mosettig and Himmelsbach. ... 

There are a number of other synthetic substances analogous with or approximating to the cinchona alkaloid structure which it is more convenient to deal with in discussing the correlation of chemical structure with pharmacological action in this group (p. 469). 

The conductivity of membranes that do not contain dissolved ionophores or lipophilic ions is often affected by cracking and impurities. The value for a completely compact membrane under reproducible conditions excluding these effects varies from 10-8 to 10 10 Q 1 cm-2. The conductivity of these simple unmodified membranes is probably statistical in nature (as a result of thermal motion), due to stochastically formed pores filled with water for an instant and thus accessible for the electrolytes in the solution with which the membrane is in contact. Various active (natural or synthetic) substances... 

In practically all natural and in most synthetic substances there are, mixed with the major components, impurities in minor and trace amounts. Minor components occur in concentrations below 1 % and down to about 0.1% of the total weight of a sample of the substance. Many additional impurities, usually referred to as trace components or trace elements, occur in host substances at extremely low concentration, generally below 0.1% their concentration is generally expressed either as parts per million (ppm) or parts per billion (ppb) (1 ppm is equivalent to a one gram in one ton 1 ppb, to one gram in one million tons). Minor and trace impurities do not alter the basic composition, nor do they affect most of the properties of substances, but they may change, even drastically, some of their physical properties. Trace impurities in otherwise colorless minerals, for example, often make the minerals highly colored. 

The adhesive cements, or simply adhesives, are viscous liquid preparations used mainly for joining together different objects or parts of objects into coherent units, for sizing (sealing) porous surfaces, and as binders in the preparation of paints (see Textbox 18). Until the end of the nineteenth century the only adhesives known to humans were of natural origin, derived either from vegetable secretions or from animal fluids and tissues. Few modern adhesives are now derived from natural substances most are artificial, human-made (synthetic) substances developed since the twentieth century. 

Dirt is attracted to and held on the skin and clothing mostly by fats and oils that are insoluble in water. Soap, an artificial, human-made (synthetic) substance, cleanses by making fats and oils dispersible in water soap acts as an emulsifier, a substance that disperses solids into liquids in which they are usually immiscible. When used as a body cleanser, for example, soap combines with oils and fats together with dirt particles on the skin, emulsifying and dispersing them in water in such a way that they can be disposed of with the water. 

The interpretation of the analytical data obtained from ancient materials relies on a good knowledge of the various natural or synthetic substances that may be involved in the samples investigated. Accordingly, we describe here the main characteristics of waxes, animal fats and vegetable oils, not only from a chemical point of view, but also considering their properties, origin and uses. 

Naturally occurring hydrated silicates of calcium and aluminium the name is also given to synthetic substances with a similar crystalline structure used as the basis of molecular sieves. ZEPC... 

Riboflavin-5-phosphate (ElOla). This material is both less bitter and more water stable than riboflavin. It is normally only encountered as a pure synthetic substance. Like riboflavin it is used on panned products. 

There exists a list of permitted additives. This list is concerned only with chemical synthetics (substances obtained by a chemical reaction other than degradation). It means that the substances on the list are those which either do not occur naturally or are not obtained from natural sources. Of the substances which are not on the list it is not always possible to decide whether these may be used in food. The antioxidants and foodstuffs in which a limited amount of antioxidant is permitted are given in Table 12.11. Only the above-mentioned foods may contain antioxidants, except -tocopherol which may be generally used in foods as an antioxidant. 

The ambition of the OSPAR Commission, moreover, as manifested in the Objective of the Strategy aims at continuously reducing discharges, emissions and losses of hazardous substances (as defined In Annex 1) with the ultimate aim of achieving concentrations In the marine environment near background values for naturally occurring substances and close to zero for man-made synthetic substances. ... 

A different direction in ion-selective electrode research is based on experiments with antibiotics that uncouple oxidative phosphorylation in mitochondria [59]. These substances act as ion carriers (ionophores) and produce ion-specific potentials at bilayer lipid membranes [72]. This function led Stefanac and Simon to obtain a new type of ion-selective electrode for alkali metal ions [92] and is also important in supporting the chemi-osmotic theory of oxidative phosphorylation [69]. The range of ionophores, in view of their selectivity for other ions, was broadened by new synthetic substances [1,61]. 

During further research, many natural and synthetic substances with macrocyclic structures were discovered that as a rule are not charged and have the following properties in common (see [169]) ... 

The manufacture and supply of synthetic substances surpass (as do some other interventions of modem technologies ) the needs and expectation horizons of society. In the case of reflexive modernization (i.e. reflecting its own bases and prerequisites), one of the central problems is dealing with not yet knowing and... 

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