Precipitation criteria

Recalling the previous assertion that efficient fractionation requires liquid-liquid phase separation, we conclude that nitrobenzene and amyl acetate should be satisfactory solvents from which to fractionate polyethylene by successively lowering the temperature and that the better solvent xylene should be avoided for this purpose. The character of the phase diagram may, in fact, be used as a criterion of the efficacy of a given solvent for fractionation (see Chap. VIII, p. 344). If the curve representing the precipitation temperature plotted against concentration rises monotonically, crystalline separation is clearly indicated if it passes through a maximum at a low concentration, liquid-liquid separation is virtually assured, and the solvent may be assumed to be a satisfactory one to use for fractionation. 

The voltammograms at the microhole-supported ITIES were analyzed using the Tomes criterion [34], which predicts ii3/4 — iii/4l = 56.4/n mV (where n is the number of electrons transferred and E- i and 1/4 refer to the three-quarter and one-quarter potentials, respectively) for a reversible ET reaction. An attempt was made to use the deviations from the reversible behavior to estimate kinetic parameters using the method previously developed for UMEs [21,27]. However, the shape of measured voltammograms was imperfect, and the slope of the semilogarithmic plot observed was much lower than expected from the theory. It was concluded that voltammetry at micro-ITIES is not suitable for ET kinetic measurements because of insufficient accuracy and repeatability [16]. Those experiments may have been affected by reactions involving the supporting electrolytes, ion transfers, and interfacial precipitation. It is also possible that the data was at variance with the Butler-Volmer model because the overall reaction rate was only weakly potential-dependent [35] and/or limited by the precursor complex formation at the interface [33b]. 

PRK is the primary design criterion for landfill covers that are expected to limit and control the amount of precipitation that enters the waste of the landfill. As a result, the primary focus of model... 

An aridity definition that takes account of the relation precipitation/potential evaporation is the Aridity Index used in the Atlas of Desertification (UNEP, 1993). Four different degrees of aridity can be recognized. These are best defined using the Aridity Index (AI), calculated as the ratio P/PET, where P stands for precipitation and PET for (potential) evapotranspiration. AI values of <1.0 indicate an average annual moisture deficit. According to this criterion, four subzones can be discussed ... 

In recent studies, pesticides such as atrazine have been found in precipitation. Therefore volatilization and subsequent transport in the gaseous phase is an important environmental pathway. Vaporization rates of pesticides deposited on surface of soil and plant leaves depend on the physical-chemical properties of the substance. A useful physicochemical criterion is Henry s constant, Ku, which is defined as the equilibrium air-to-water partial pressure ratio of the substance (see Chapter 7). 

Finally, even if these criteria are satisfied, there remains the question of whether the product will adhere to form a film or just precipitate homogeneously in the solution. This is the most difficult criterion to answer a priori. The hydroxide and/or oxy groups present on many substrates in aqueous solutions are likely to be quite different in a nonaqueous solvent (depending on whether hydroxide groups are present or not). Another factor that could conceivably explain the general lack of film formation in many organic solvents is the lower Hamaker constant of water compared with many other liquids this means that the interaction between a particle in the solvent and a solid surface will be somewhat more in water than in most other liquids (see Chapter 1, van der Waals forces). From the author s own experience, although slow precipitation can be readily accomplished from nonaqueous solutions, film formation appears to be the exception rather than the rule. The few examples described in the literature are confined to carboxylic acid solvents (see later). 

In the three studies performed on vial/ampoule washer using X ml size, the vial/ampoule washer should meet soil test acceptance criterion, i.e., negative (free from precipitates). 

The vial/ampoule washer met the soil test acceptance criterion. All ten vials/ampoules were found negative (free from precipitates). The vial/ampoule washer was approved for X ml vial/ampoule washing. 

Kekule s instability criterion failed completely in the case of many coordination compounds, which were classified as molecular compounds by sheer dint of necessity although they were extremely resistant to heat and chemical reagents. For example, although hexaamminecobalt(III) chloride contains ammonia, it neither evolves this ammonia on mild heating nor does it react with acids to form ammonium salts. Also, addition of a base to its aqueous solution fails to precipitate hydrated cobalt(III) hydroxide. 

The titration must be performed under vigorous stirring, because the AgSCN precipitate has a tendency to adsorb silver ions. Thus stirring minimizes this adsorption process and all the silver ions will be titrated properly. A criterion of the true end point is that the color will be stable for 1 min. 

Even if a system is irreducibly complex (and thus cannot have been produced directly), however, one can not definitively rule out the possibility of an indirect, circuitous route. As the complexity of an interacting system increases, though, the likelihood of such an indirect route drops precipitously. And as the number of unexplained, irreducibly complex biological systems increases, our confidence that Darwin s criterion of failure has been met skyrockets toward the maximum that science allows. 

According to this method, DNA is treated with SI nuclease after hybridization and then precipitated. SI nuclease digests single-stranded DNA but not double-stranded DNA. The rigor of enzyme treatment can have a dramatic effect on the effective criterion, and it is important to establish strict control in SI nuclease assays. 

Nonahydridorhenate reacts slowly with acetonitrile to give a brown product. If the solution becomes dark brown, the precipitate will be colored. The impurity is intensely colored, and the sample color is not a good criterion of analytical purity. 

In the preceding discussions, a criterion for stability was established using the equilibrium constant called K,p. At normal conditions, as especially used in the water works industry, specialized forms of water stability criteria have been developed. These are saturation pH, Langelier index, and the precipitation potential of a given water. 

Figure 11.1 shows a pipe that is almost completely blocked due to precipitation of CaC03. Precipitation potential is another criterion for water stability, and application of this concept can help prevent situations like the one shown in this figure. Understanding this concept requires prerequisite knowledge of the charge balance. 

Again, as in previous chapters, the best place to investigate for determining the modes of removal is the table of solubility products constants as shown in Table 14.1. A precipitation product that has the lowest K p means that the substance is the most insoluble. As shown in the table, the phosphate ion can be precipitated using a calcium precipitant producing either Ca5(P04)3(0H)(j) or Ca3(P04)2. Of these two precipitates, Ca5(P04)3(0H)(j) has the smaller K p of 10" thus, it will be used as the criterion for the precipitation of phosphates. Ca5(P03)3(OH)(j) is also called calcium hydroxy apatite. 

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