Electrical conductivity methods

Electrical conductivity methods for the determination of phosgene are particularly amenable to automation, and several potentially suitable gas analysers have been described [2093a], 

Phosgene may be detected by the variations in the electrical resistance of a heated wire of palladium-silver alloy surrounded by the gas [1706], Methods based upon the electrical conductance of solutions, however, depend upon the production of ionic compounds for their measurement [1173,2093a], and are particularly susceptible to interference from hydrogen chloride. 

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Electrolytes, depending upon their strength, dissociate to a greater or less extenl in polar solvents. The extent to which a weak electrolyte dissociates may be determined by electrical conductance, electromotive force, and freezing point depression methods. The electrical conductance method is the most used because of its accuracy and simplicity. Arrhenius proposed that the degree of dissociation, a. of a weak electrolyte at any concentration in solution could be found from the rutio of the equivalent conductance. A. of the electrolyte at the concentration in question to (he equivalent conductance at infinite dilution A0 of the electrolyte. Thus... 

In summary, the effect of porosity on electrical conductivity and ion diffusivity in agarose gels is studied. Both electrical conductivity and ion diffusivity increase with porosity. The model obtained from the electrical conductivity data, i.e., Equation (7), can predict the diffusivity of macromolecules in 2% agarose gel for solutes with hydrodynamic radius less than the pore size of the gel. This study suggests that electrical conductivity method used in this study can be applied to investigating diffusion behavior of macromolecules in uncharged porous media. 

In order to investigate those temperature sensing difficulties the same group have recently presented an electrical conductivity method for in situ temperature monitoring within the capillary flow reactor under microwave ir-... 

Hantzsch tried to obtain further evidence for the existence of the above mentioned ions, using the electric conductivity method but without success. Finally he tried to isolate the sulphates of the two hypothetical ions nitracidium Mid hydro-nitracidium ... 

Corrosion and Ionisation.—Iron will remain untarnished for indefinite periods in the presence of concentrated solutions of the carbonates of the alkali metals, even in the presence of small quantities of other salts. If, however, the alkali carbonate is very dilute, it cannot entirely inhibit corrosion. Now, the minimum quantities of alkali carbonate required to inhibit the corrosive actions of a given concentration of various other salts of the same alkali metal have been determined.1 The results show that, if the added salts are arranged in order according to the amount of alkali carbonate required to inhibit corrosion, they are also not merely in the order of the relative strengths of their acid radicles, but the relative quantities of carbonate bear a general relationship to the numerical values found for the strengths of the acids by electrical conductivity methods. This is well illustrated in the following table —... 

The electric conductivity methods are widely used in both categories because they are simple to operate and give quick response, accurate results, and a continuous reading that is, they can be used as a measuring element in any control loop. 

The value of the percentage hydrolysis for = 32 is 2 58, which agrees well with that found by Bredig by the electrical conductivity method, namely, 2 61. 

If the fluid film separating two metallic bounding surfaces is an electrical insulator, then loss of insulating behavior and appearance of conductance can be interpreted as contact between these surfaces. This is the premise behind the electrical conductance method of detecting lubricant film failure. A practical limit on the applicability of this premise is electrical breakdown of the fluid as thinning of the film concentrates the field intensity. Another complication arises from the fact that for the structured surfaces of every day experience first contact is at the highest asperities rough surfaces may therefore come into initial contact sooner than indicated by the overall trend of the resistance measurements. 

Reaction Monitoring Using the Electrical Conductivity Method.341... 

Electrical Conductivity Method for In Situ Monitoring of Radiation Reactions... 

If untransformed, raw, conductivity data are used it is much easier to correctly determine boundary conditions for the calculation of reaction extent (symbols are the same as in Equation 13.6). By using Equation 13.7 not only the aforementioned errors are avoided but also the full sensitivity of the electrical conductivity method is attained. Because of that, logarithmic transformation of electrical conductivity should be avoided for reaction rate calculations and otherwise used only on the basis of a proven physical law (like the Arrhenius law). 

PROPERTIES OF NANOMATERIALS RELEVANT TO REACTION MONITORING BY THE ELECTRICAL CONDUCTIVITY METHOD... 

Several examples are presented to provide better insight into the scope of information that can be acquired using the electrical conductivity method for monitoring of reacting systans, focused on but not limited to radiation-induced reactions and nanomaterials. 

The electrical conductivity method is one of the very few experimental techniques that can be used for in situ monitoring of radiation-induced chemical and physical changes. Sensitive measuring equipment is easily kept outside the radiation field, while the parts that sustain radiation damage are relatively cheap and easily replaceable. A major drawback of the conductivity method is that it does not provide direct chemical information, but the problem can be solved by comparing to results obtained by other methods that cannot be used directly in the radiation field. 

The outdated approach to use logarithmic transformation without any physical evidence for it should be avoided wherever possible (not only in reaction monitoring by electrical conductivity). The argumentation presented should be convincing enough to justily use of conductivity data itself to attain full sensitivity of the electrical conductivity method and to observe a variety of subtle reaction and structural changes. 

Materials. Dodecylpyridinium bromide was synthesized by treating fractionally distilled 1-dodecane bromide in dry pyridine for 12 hr. The crude surfactant was recrystallized twice from acetone followed by decolorization with active charcoal in methanol solution. The resulting white crystal is a monohydrate of DoPBr. The critical micelle concentration (CMC) in aqueous solution as determined by electric conductivity method is 17.4 mM at 30°C in agreement with literature. Calf thymus DNA (sodium salt, SIGMA) was used as received. Residual (nucleotide) concentration was determined by a colloid titration using poly(potassium vinyl sulfate) as a titrant and Toluidine Blue as an indicator. 4 Propionyl- a-cyclodextrin (prop- a-CD) used as a neutral carrier was prepared by esterification of a-cyclodextrin (Tokyo Kasei Co.) with propionic anhydride in dry pyridine at room temperature for 12 hr. The reaction mixture was poured onto ice to obtain a gummy product which was then dissolved in acetone and precipitated in cold water. The dissolution-precipitation was repeated three times. The hydrophobicized oc-CD is a white powder. 

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