Classification of simple substances

Since the Mithode is silent on the specific kinds of properties according to which these traditional classes were distinguished, we can be fairly sure that the definitions 

1 In the following, we presuppose the description of the table given in chapter 5. In referring to the table s fields—field I/a, etc.—we refer to the diagrams in that chapter, particularly figure 5.4. 

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Only at the end of the article were there a few words about Mendeleev s note. Boisbaudran admitted that he had read it with great interest since classification of simple substances interested him for a long time. He had never known about Mendeleev s prediction of eka-aluminium properties but it did not matter Boisbaudran believed that his discovery of gallium was facilitated by his own laws of spectral lines of elements with similar chemical properties. In his opinion, spectral analysis played a decisive role. And not a word that Mendeleev in his prediction of eka-aluminium also underlined the prominent role of spectral analysis in the discovery of the new element. According to Boisbaudran, Mendeleev s predictions had nothing to do with the discovery of gallium. 

Various separation methods have been used to isolate, fractionate, and characterize humic materials. Originally it was fractionation, based on solubility differences of humic components in diluted alkalis and acids, which laid the ground work for the first classifications of humic substances (HS) in the 19th century (Mulder, 1861 Sprengel, 1837) and provided for operational definition of HS (Kononova, 1966). And now, alkali extraction is the method of choice for isolating HS from solid humus-containing substrates like soil, peat, coal, and so on (Swift, 1996), while hydrophobic resins (e.g., Amberlite XAD resins) are typically used to extract HS dissolved in natural waters (Aiken, 1985). Initial research on HS began with the used simple separation methods to prove, examine, and define characteristics of components of humic matter (Oden, 1919).Today, however, advances in HS research require ever more sophisticated techniques of separation combined with structural analysis (Orlov, 1990 Stevenson, 1994). 

Much has been written on the Methode de nomenclature chimique, and much has been said in praise of the Tableau of the Methode and its outstanding significance in the history of early modem chemistry. But despite this unanimously shared assessment and appreciation, no thorough and exhaustive analysis of the Tableau s classification of chemical substances has been presented by any historian of science up to now. Only the first column of the table, the column for simple substances, was hitherto subjected to closer inspection. Thus our analysis of the table s classification cannot build on the results of earlier investigations, but has to start from scratch. This means we first have to provide an overview on the table to which we can refer and return whenever desirable in the course of the subsequent investigations. In what follows we will first describe the arrangement of the table and then analyze its classification s formal features. 

Not for formal but for functional reasons, the table could not render these relations for the last two classes of simple substances. Otherwise the tableau would have lost its unambiguity, as the same compounds would have occurred at different places. In chapter 10 we will come back to the problem of overlapping classes in non-encaptic classifications like our Tableau. 

As shown in the previous chapter, the Tableau provided six classes for the genera of pure chemical substances one for the genera of simple substances and five for the genera of different types of compounds. This most principal feature of its classifica-tory strucmre relied on two premises. It was first assumed that the chemical substances in question could be divided into either simple substances or compounds and second, that all chemical compounds were classified according to their chemical composition. Classification according to composition is, therefore, the most fundamental chemical principle embodied in the classificatory structure of the table. 

The aim of the present article is to elevate the role of triads to an even greater extent. Since triads are now expressed in terms of atomic numbers they coincidentally characterize the elements as basic substances. In other words they characterize the true basis for periodic classification compared with the elements as simple substances, as argued by Mendeleev and more recently by Paneth and other authors. 

As suggested in the title of the present article, we believe that the periodic table, which initially arose from the discovery of atomic weight triads, can now be further enhanced by recognizing the fundamental importance of atomic number triads. In addition one should recognize the more fundamental nature of the elements as basic substances rather than as simple substances, and that the periodic system is primarily a classification of the former. Whereas we previously suggested that these aims were best served by the left-step table we now favor the revised left-step table shown in Figure 3. 

Bent claims that the periodic system should be primarily based on the structure of neutral atoms rather than on macroscopic properties of the elements. In doing so he claims support from none other than Mendeleev. Bent also claims to garner support from the writings of Mendeleev in steering clear of the properties of the elements as simple substances in crucial matters of classification of the elements. In fact, the identification of elements as basic substances with the atoms of the elements is... 

A distinction between a solid and liquid is often made in terms of the presence of a crystalline or noncrystalline state. Crystals have definite lines of cleavage and an orderly geometric structure. Thus, diamond is crystalline and solid, while glass is not. The hardness of the substance does not determine the physical state. Soft crystals such as sodium metal, naphthalene, and ice are solid while supercooled glycerine or supercooled quartz are not crystalline and are better considered to be supercooled liquids. Intermediate between the solid and liquid are liquid crystals, which have orderly structures in one or two dimensions,4 but not all three. These demonstrate that science is never as simple as we try to make it through our classification schemes. We will see that thermodynamics handles such exceptions with ease. 

Virases are much simpler organisms than bacteria, and they are made from protein substances and nucleic acid. A single nucleoprotein molecule formed from molecules of nucleic acid that are chemically bound to a bulky protein molecule can be considered a simple viral particle. The protein molecule plays the role of a protective membrane. Thus the virus can be schematically described as a nucleic acid insert that is protected by a protein covering. A virus can contain either ribonucleic acid or deoxyribonucleic acid, but it never contains both of them together. The type of nucleic acid is the basis of one of the classifications of viruses. Viruses are obligatory intracellular parasites, which, upon entering a cell (i.e. after being infected) use many biochemical systems of the host cell. 

As mentioned previously, the authorization process starts with the identification of a substance as substance of very high concern (SVHC). For this purpose, the ECHA on behalf of the European Commission or a member state competent authority prepares a dossier. It generally includes a proposal for the identification of a substance as SVHC, a justification for this proposal and information on the substance s use, exposure, and risks as well as on alternatives. The extent of the justification may differ considerably between substances and may range from a sophisticated assessment of the harmful effects caused by the substance to a simple reference to Annex VI Part 3 of the CLP Regulation if a harmonized classification... 

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