Systems with Variable Chemical Activities

There are zeolite-bearing rocks in which one mineral is apparently being replaced by another mineral under constant P-T conditions. This indicates a system in which certain chemical components appear to be perfectly mobile a system in which the total number of phases that can coexist at equilibrium is reduced as a function of the number of chemical components which ar e internal variables of the system. Two examples of this type of equilibrium concerning zeolites can be cited saline lakes and analcite-bearing soil profiles (Hay, 1966 Hay and Moiola, 1963 Jones, 1965 and Frankart and Herbillon, 1970). In both cases a montmorillonite-bearing assemblage becomes analcite or zeolite-bearing at the expense of the expandable phyllosilicate. Other phases remain constantly present. 

If one considers the fluids in these soils and terrestrial lakes as having 

These observations.are confirmed in a list of the minerals encountered in each sample investigated. In this list, it is striking to see that 

Chemical analysis of the pyroclastic material indicates that the major oxides present are AljO, an 2 We assume 

Na and Ca to play equivalent roles in zeolites, as well as K, and if we consider A1 and Si as the major variables combined with K and Na in the phyllosilicates, we can adequately represent the phases in a (Ca-Na)-K-Al-Si system where H O is in excess in the fluid phase. If the system has four chemical variables and the natural assemblages are frequently found to contain four authigenic minerals, we must assume that most chemical variables are inert or extensive variables of the chemical system which controlled the crystallization of the zeolite-clay mineral containing sediments.  

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The use of a chemical agent as an anti-foam is affected by an on-off algorithm with variable dosing time and time delay. If the presence of foam is detected, then the controller first activates a delay timer. This type of foam controller works with some delay and variable dosing time. If at the end of the delay period the foam is still present, then the dosing pump is activated and chemical agent is added to the bioreactor. If the foam is still detected at the end of this period, the combined system of delay and dosing is reactivated. With this method of controller, addition of any unnecessary anti-foam is prevented. 

Drugs are chemical entities, precisely measurable and controllable within close tolerances. Tolerances can be established on the product, and within these tolerances one can live with the drug. If the dmg is out of specification, it is beyond these tolerable limits. It is very different for biologics. The [Code of Federal Regulations] definition is that a biologic involves the product, the manufacturing activity, the product facility, and the people. Inherent natural variability exists at every stage of the process, at every element of the system. Some variability is controllable some is never controllable. 

It is evident then that the number of phases present can be reduced by restricting the intensive variables to non-unique or inter-dependent conditions and thus a general case" is valid. As the number of chemical components which are perfectly mobile (intensive variables) increases, the number of phases will be decreased. Thus a rock banded in mono-mineralic zones, such as is commonly found in hydrothermal deposits, indicates a system with few inert components. The zonation most commonly represents gradients of the extensive variables temperature and chemical activity of ionic species in aqueous solution. However, it is not always easy to determine which variables are active in a given sequence of mineral bands related to an alteration source. 

The quaternary ammonium compounds (qv) are manufactured by the reaction of an alkyl halide with a tertiary amine. The alkyl halide may be short-chain, long-chain, or benzyl. Selection of a long-chain alkyl group yields structures with variable composition and greatly adds to the chemical complexity inherent in this group. Investigation of structure-activity relationships has led to claims for superior efficacy or compatibility, most notedly with anionic surfactants in disinfectant-detergent cleaner systems, of closely related compounds in the family. 

In my opinion, an active centre of alkene polymerization in the liquid phase is not a single chemical entity to be visualized by a single (and simple) chemical formula. Probably a set of compounds, of complexes with variable composition, a dynamic system where the effects of individual components are mutually complementary or overlapping is really in play. The same macroscopic effect (centres of equal activity and iso-specific regulating ability) can be obtained with various starting organometals and donors. In such a system, subsystems may exist each of which is externally manifested as an individual active centre (rapid or slow, isotactic, with a tendency to transfer or termination, or living, etc.) [225],... 

The states of a system are modified by variable tuning and energy exchanges. In chemically active venues, the states alter spontaneously and with purpose in collaboration with the surroundings. This chapter considers an unusual type of thermodynamic transformation by way of chemical reactions. 

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