Paneth

Stem layer adsorption was involved in the discussion of the effect of ions on f potentials (Section V-6), electrocapillary behavior (Section V-7), and electrode potentials (Section V-8) and enters into the effect of electrolytes on charged monolayers (Section XV-6). More speciflcally, this type of behavior occurs in the adsorption of electrolytes by ionic crystals. A large amount of wotk of this type has been done, partly because of the importance of such effects on the purity of precipitates of analytical interest and partly because of the role of such adsorption in coagulation and other colloid chemical processes. Early studies include those by Weiser [157], by Paneth, Hahn, and Fajans [158], and by Kolthoff and co-workers [159], A recent calorimetric study of proton adsorption by Lyklema and co-workers [160] supports a new thermodynamic analysis of double-layer formation. A recent example of this is found in a study... 

The second set of experiments was carried out in 1929 by Paneth. The decomposition of tetramethyllead was carried out in such a way that the decomposition products were carried by a flow of inert gas over a film of lead metal. The lead was observed to disappear with re-formation of tetramethyllead. The conclusion was reached that methyl radicals must exist long enough in the gas phase to be transported from the point of decomposition to the lead film, where they were reconverted to tetramethyllead. 

What actually converted me to the left-step table, at least for a period of a few years, was a rather concise paper by the periodic table designer Gary Katz, which appeared in The Chemical Educator.20 My own support for this form of the table centered on my interest in the dual sense of the term element and in particular the more fundamental sense, called element as a basic substance by Paneth. 

What I hope to have added to the discussion has been a philosophical reflection on the nature of the concept of element and in particular an emphasis on elements in the sense of basic substances rather than just simple substances. The view of elements as basic substances, is one with a long history. The term is due to Fritz Paneth, the prominent twentieth century radio-chemist. This sense of the term element refers to the underlying reality that supports element-hood or is prior to the more familiar sense of an element as a simple substance. Elements as basic substances are said to have no properties as such although they act as the bearers of properties. I suppose one can think of it as a substratum for the elements. Moreover, as Paneth and before him Mendeleev among others stressed, it is elements as basic substances rather than as simple substances that are summarized by the periodic table of the elements. This notion can easily be appreciated when it is realized that carbon, for example, occurs in three main allotropes of diamond, graphite and buckminsterfullenes. But the element carbon, which takes its place in the periodic system, is none of these three simple substances but the more abstract concept of carbon as a basic substance. 

Instead I propose a more radical solution, namely that of not identifying bonded atoms with elements as basic substances, a view for which I claim support from the work of Mendeleev and Paneth. This does not solve the problem of redesigning a periodic table to reflect the behavior of bonded atoms. But if we are to retain the traditional periodic table of neutral atoms, we may still forge a connection with elements as basic substances by arranging the elements so as to maximize atomic number triads, where atomic number may now be interpreted to also mean element number . 

Figure 4. Comparison ol periodic tables given by Paneth 42) and Seaborg 44).

And other heuristic guides could kick in to give plausible, but never deductively derived, predictions . (So, for example, Paneth in the 1920s used simple reasoning based on the Periodic Table to predict that then undiscovered hafnium would occur in the same ores as zirconium. This is nonetheless a considerably looser notion of prediction than applies to standard cases from physics. See Scerri, 1994). 

To state the distinction otherwise, simple substances are the manifestation of the elements considered as basic substances, the latter being the more fundamental of the two senses of the term element . Admittedly the terminology is a little unfortunate since the labels basic and simple appear to place the two senses of the term element on the same epistemological level. The intention however is that basic substances are to be regarded as more fundamental. Be that as it may, we will retain Paneth s terminology in view of the importance of the writings of this author in which the distinction is perhaps more clearly established than elsewhere in the literature (5). 

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. 

There has been some discussion as to whether the word "substance" is appropriate in this context. For example, Earley believes it is not because it implies a form of materiality which is not intended [21. In this article, the word "substance" will be used, however, because of the terminology coined by Paneth when he drew his distinction between the two senses of the term "element." However, Paneth actually uses the German words "grundstuff" and "einfacherstuff" which were translated as basic substance and simple substance, respectively, in the article that appeared in the British journal for the Philosophy of Science and which has been most widely read. 

But what would become of Mendeleev s periodic system which now seemed to consist of 300 or so "elements" To some chemists, the discovery of isotopes implied the end of the periodic system as it was known.3 These chemists suggested that it would be necessary to consider the individual new isotopes as the new "elements." But the chemist Paneth adopted a less reductionist approach, arguing that the periodic table of the familiar chemical elements should be retained because it dealt with the "elements" that were of interest to chemists. A justification for this view was provided by the fact that, with a few exceptions, the chemical properties of isotopes of the same element are indistinguishable.4 Moreover, Paneth appealed to Mendeleev s distinction between the two senses of the concept of an "element" in order to provide a philosophical rationale for the retention of the chemist s periodic table. Paneth argued that the discovery of isotopes of the elements represents the discovery of new elements as simple substances, whereas periodic... 

This fact was verified experimentally by Paneth and Hevesy, who found that the redox potentials of bismuth cells containing different isotopes of the metal produced indistinguishable values. 

Indeed, the terminology of element as basic substance as opposed to as simple substance, which has been used throughout this article, originates with this work of Paneth. 

But I would like to suggest that Mendeleev, and now Bent, are incorrect in drawing this identification. Nor do I claim any originality in pointing out Mendeleev s error because this was already clearly stated by Paneth in a couple of articles written in the 1930s. 

It was suggested earlier that Schwarz s identification of bonded atoms with elements as basic substances represents a step in the right direction. This notion will now be examined more carefully, since it too will be found lacking in a rather fundamental way, which was hinted at in some earlier quotations from Paneth. The concern voiced by Paneth regarding associating elements as basic substances with neutral atoms was due to the fact that these concepts inhabit different epistemological levels. This is equally true of the identification of elements as basic substances with bonded atoms, which is the identification that Schwarz supports. 

Instead of identifying elements as basic substances with neutral atoms (Bent and Weinhold and almost everybody else) or elements as basic substances with bonded atoms (Schwarz), I would like to propose just focusing on elements as basic substances in Paneth s macroscopic sense. The one ma-... 

Westaway KC, T Koerner, Y-R Fang, J Rudzinski, P Paneth (1998) A new method of determining chlorine kinetic isotope effects. A a/ Chem 70 3548-3552. 

Lewandowicz A, J Rudzinski, L Tronstad, M Widersten, P Ryberg, O Matsson, P Paneth (2001) Chlorine isotope effects on the haloalkane dehalogenase reaction. J Am Chem Soc 123 4550-4555. 

Paneth, F.A. Chemistry and beyond a selection from the writings. .. Interscience, 1964. 285p. 

Fig. 11.4. Model for cholinergic signalling in the intestinal mucosa, providing a possible rationale for AChE secretion by parasitic nematodes. ACh released from enteric cholinergic motor neurons stimulates chloride secretion, mucus secretion and Paneth cell exocytosis through muscarinic receptors. Secretory responses may be modulated by mast cell mediators, either directly or via the induction of neural reflex programmes. The role of muscarinic receptor-positive cells in the lamina propria of rats infected with N. brasiliensis is undetermined, as are potential mechanisms of trans-epithelial transport of the enzymes. Adapted from Cooke (1984).

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