Classification of Substances

The hazards of a rigid classification of substances which may modify the course of a free radical polymerization are well illustrated by the examples of inhibitors and retarders which have been cited. The distinction between an inhibitor or retarder, on the one hand, and a co-monomer or a transfer agent, on the other, is not sharply defined. Moreover, if the substance is a free radical, it is potentially either an initiator or an inhibitor, and it may perform both functions as in the case of triphenylmethyl. If the substance with which the chain radicals react is a molecule rather than a radical, three possibilities may arise (i) The adduct radicals may be completely unreactive toward monomer. They must then disappear ultimately through mutual interaction, and we have a clear-cut case of either inhibition or retarda-... 

British Toxicology Society (1984). A new approach to the classification of substances and preparations on the basis of their acute toxicity. A report by the British Toxicology Society Working Party on Toxicology. Human Toxicol. 3 85-92. 

Classification of substances often results in some unsatisfactory results, and food additives are no exception. In the evaluation of food additives, functional use is a helpful way of categorising additives. Functional use and level of incorporation are important considerations in assessing the likely intake by consumers. Use and intake level are clearly linked, as the functional effect depends on the amount added. The level of use may be self-limiting by organoleptic considerations. However, whilst it is logical to have functional use as a classification, many additives have more than one functional use, and some could be described as having multiple uses. International documentation differs in its treatment of functional uses. The European Council legislation has three broad classifications ... 

The primary classification of substances made by the alchemists was expressed by saying these substances are rich in the principle sulphur, those contain much of the principle mercury, and this class is marked by the preponderance of the principle salt. The secondary classification of the alchemists was expressed by saying this class is characterised by dryness, that by moisture, another by coldness, and a fourth by hotness the dry substances contain much of the element Earth, the moist substances are rich in the element Water, in the cold substances the element Air preponderates, and the hot substances contain more of the element than of the other elements. 

Kreek, Jeanne, and Marc Reisinger. 1997. "The Addict as Patient." In Substance Abuse A Comprehensive Textbook, edited by Joyce H. Lowinson, Pedro Ruiz, Robert B. Millman, and JohnG. Langrod. Baltimore, Md. Williams and Wilkins. Kuehule, John, and Robert Spitzer. 1992. "DSM III Classification of Substance Use Disorders." In Substance Abuse A Comprehensive Textbook, edited by Joyce... 

Classification of substances by their sensitivity to impact and friction is particularly important for the handling of explosives. Some explosives are known to detonate on impact, whereas others will only deflagrate. Table 4.2 presents information on the sensitivity of explosive substances to impact and friction. The values shown describe the force required to initiate the explosive compositions. 

Huheey (1983) (see Section A.3 of the Appendix) gives in Appendix J a good, concise summary of the rules for inorganic nomenclature. For the classification of substances according to structural type, see the books listed in Section A.6. Wells (1984) is specially recommended. 

Since toxicological chemistry emphasizes the chemical nature of toxic substances, classification is predominantly on the basis of chemical class. Therefore, there are separate chapters on elemental toxic substances, hydrocarbons, organonitrogen compounds, and other chemical classifications of substances. 

Information about chemical theory is easier to come by than information about chemical practice. Nonetheless, we should recognize that when chemists read tables of affinities, they had in mind not only the substances that would be produced but also the ways in which the appropriate reactions could be generated and controlled. So their explicit classification of substances through affinities was joined to an implicit classification of chemical operations. Chemical operations depend on chemical apparatus, some built for that purpose, and some available in any kitchen. 

In the Priorities for Action of the IFCS in the year 2000, the target year 2008 was set for implementation of a harmonised system, and this was endorsed by the World Summit on Sustainable Development in 2002. The system adopted in late 2002 was revised in 2005 and 2006 (UNECE 2007). Responsibility rests with the United Nations Economic and Social Council Sub-Committee of Experts on the GHS under the United Nations Economic Commission for Europe (UNECE). The target of full GHS implementation by 2008 has not been reached, but implementation is well underway. Major actors have set deadlines, such as the United States (transportation 2010) and the European Union (2010 for classification of substances and 2015 for mixtures). 

When it comes to Confidential Business Information (CBI), REACH (Tide XII) contains several provisions granting rights to companies, including protection of information regarding the full composition of preparations, the precise use and tonnage of substances and links between companies (Article 118).20 On the other hand, Article 119 explicitly lists information that shall be made publicly available by electronic means, for instance names and classifications of substances and safety-related data, unless the submitter can justify not doing so. Additional information from companies can also be made available upon request (see further in EDF 2007a). 

These developments necessitate another change in the concept of element it is now said that an element cannot be transmuted into another element by ordinary chemical methods. The discovery of these new phenomena might have led to confusion regarding the validity of the classification of substances as elementary substances and ( ompounds were it not for the fact that our knowledge of the structure and properties of atoms has also increased rapidly in recent years. In this book we have not made use of any variant of the old definition, but have, at the beginning of this chapter, defined an element as the kind of matter represented by a particular kind of atom, namely, atoms with a particular atomic number. 

The approach to classifying mixtures includes the application of expert judgement in a number of areas in order to ensure existing information can be used for as many mixtures as possible to provide protection for human health and the environment. Expert judgement may also be required in interpreting data for hazard classification of substances, especially where weight of evidence determinations are needed. 

Chemicals may be removed from some aquatic environments by volatilization. The intrinsic potential for volatilization is determined by the Henry s Law constant (H) of the substance. Volatilization from the aquatic environment is highly dependent on the environmental conditions of the specific water body in question, such as the water depth, the gas exchange coefficients (depending on wind speed and water flow) and stratification of the water body. Because volatilization only represents removal of a chemical from water phase, the Henry s Law constant caimot be used for assessment of degradation in relation to aquatic hazard classification of substances. Substances that are gases at ambient temperature may however for example be considered further in this regard (see also Pedersen et al, 1995). 

This examination has enabled a classification of substances in order of priority in relation to the risk each constitutes for the aquatic environment and human health. 

Description and classification of substances is of course not always easy, and the information provided in a UV spectrum is not always sufficient for identification, but it should be possible with the aid of this type of picture and information to classify quite rapidly some substances not included in the selection from their UV spectra, according to the chemical (and sometimes also the therapeutic) group defined by their chromophores. For example, it is logical to assume an analgesic/antipyretic classification from a pyrazolone spectrum, while conversely if a substance is thought to be a local anaesthetic, the analyst will consider p-aminobenzoic acid esters or base-substituted anilides, and will read the spectrum from this aspect. 

One of the important factors in the kinetic modeling of organic ions is their slow diffusion into the ion exchange resin. The mean diffusion time is listed in Table 6 as a function of resin particle size for different size classifications of substances.With the larger organic ions, the contact time for the feed solution and the resin must be increased to have the ion exchange take place as a well-defined process such as occurs with the rapidly diffusing ions of mineral salts. 

Table 5. Classification of substances according to various criteria...

The key point in the rheological classification of substances is the question as to whether the substance has a preferred shape or a natural state or not [19]. If the answer is yes, then this substance is said to be solid-shaped otherwise it is referred to as fluid-shaped [508]. The simplest model of a viscoelastic solid-shaped substance is the Kelvin body [396] or the Voigt body [508], which consists of a Hooke and a Newton body connected in parallel. This model describes deformations with time-lag and elastic aftereffects. A classical model of viscoplastic fluid-shaped substance is the Maxwell body [396], which consists of a Hooke and a Newton body connected in series and describes stress relaxation. 

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