Polarizers silver chloride

It is widely recognized that the solvent in which any chemical reaction takes place is not merely a passive medium in which relevant molecules perform the solvent itself makes an essential contribution to the reaction. The character of the solvent will determine which chemical species are soluble enough to enter solution and hence to react, and which species are insoluble, and thus precipitate out of solution, thereby being prevented from undergoing further chemical change. In the case of water, as will be seen, polar and ionic species are the ones that most readily dissolve. But even so, mere polarity or ionic character is not sufficient to ensure solubility. Solubility depends on a number of subtle energetic factors, and the possible interactions between water and silver chloride, for example, do not fulfil the requirements despite the ionic nature of the silver salt. Hence silver chloride is almost completely insoluble in water. 

The silver-silver chloride RE consists of a small length of silver wire or piece of silver sheet coated with a thin layer of silver chloride (this layer can be deposited by anodic polarization of the silver in chloride-contaiifing solution) and dipping into HCl or KCl solutions of defined concentration its E° = 0.2224 V. 

In individnal cases, anodic polarization of metals in electrolyte solntions will pro-dnce snrface layers (adsorbed or phase) which instead of oxygen, contain the soln-tion anions. Thns, anodic polarization of silver in chloride-containing solntions yields a snrface layer of silver chloride, while the anodic polarization of lead in snl-fnric acid solntion yields a lead sulfate layer. Layers of sulhdes, phosphates, and other salts can be formed in the same way. In many respects the properties of such salt layers are analogous to those of the oxide layers. 

We have already mentioned that silver chloride is readily soluble in liquid ammonia. Because it is slighdy less polar than water and has lower cohesion energy, intermolecular forces make it possible for organic molecules to create cavities in liquid ammonia. As a result, most organic compounds are more soluble in liquid ammonia than they are in water. Physical data for liquid ammonia are summarized in Table 10.2. 

Electrochemical oxidation-reduction of eluting mixture components is the basis for amperometric electrochemical detectors. The three electrodes needed for the detection, the working (indicator) electrode, reference electrode, and auxiliary electrode, are either inserted into the flow stream or imbedded in the wall of the flow stream. See Figure 13.13. The indicator electrode is typically glassy carbon, platinum, or gold, the reference electrode a silver-silver chloride electrode, and the auxiliary a stainless steel electrode. Most often, the indicator electrode is polarized to cause oxidation of the mixture components... 

Dichroic IR spectra were obtained using a silver chloride pile-of-plates polarizer in a Beckman IR9 spectrometer. Spectra were recorded at 25°C, usually at a scan speed of 40 cm per minute. Details are contained in... 

A second area in which polarization effects show up is the solubility of salts in polar solvents such as water. For example, consider the silver halides, in which we have a polarizing cation and increasingly polarizable anions. Silver fluoride, which is quite ionic, is soluble in water, but the less ionic silver chloride is soluble only with the inducement ofcomplexing ammonia. Silver bromide is only slightly soluble and silver iodide is insoluble even with the addition of ammonia. Increasing covalency from fluoride to iodide is expected and decreased solubility in water is observed. 

Fig. 12. Design of the galvanic cell with a flat liquid-liquid interface. (A) The four-electrode type of cell with the aqueous (w, w ) and the organic solvent (o) phases, silver/silver chloride reference electrodes (1,4), platinum counter electrodes (2, 3), a glass barrier with a round hole for the liquid-liquid interface (5) and a tube connected to a syringe for adjustment of the interface. (After [158]). (B) The two-electrode type of cell with the aqueous (1,3) and organic solvent (2) phases, water jacket (4), PTFE silicone rubber (5), silicone rubber cap, silver/silver chloride reference electrodes (7,8), glass tube (9) and polarized working (w) or nonpolarized reference (r) interface. (After [42]).

Figure 2. Polarized IR absorption spectrum of a collapsed monolayer of poly(y-n-decyl-i.-glutamate) air dried on a silver chloride plate.

Experimentally, the spectrographic technique is rather simple once a suitable sample is obtained. Almost any conventional IR spectrometer can be adapted for polarized light studies by inserting in the opticzil path a polarizing unit consisting of a stack of six to twelve silver chloride sheets inclined at an angle of about 65° to the optical path (e.g., see 463, 1334, 1168). >... 

Radiometer pOz electrode, type E 5046 consists of a platinum cathode (20 /am diameter) and silver-silver chloride reference electrode placed in an electrochemical solution behind a 20 /am thick polypropylene membrane. A polarizing voltage of about 650 mV is applied. The polarographic current is about 10 " A per mm Hg of oxygen tension at 38°C. Zero current is lower than 10 A, response time less than 60 sec at 38°C 99% of full deflection. The PO2 electrode is used with the pH-Meter 27 GM or the Astrup Micro-Equipment, in conjunction with the Oxygen Monitor. The scale can be calibrated to the range 0-100 mm Hg p02. Thermostated cells provide measurements at constant temperature of volumes down to 70 /al. The small volume makes this cell useful to measure the PO2 of capillary blood. The cell is supplied with accessories for blood sampling. 

The silver chloride cathode reaction is given by Eq. (8) in reverse that is, silver chloride is reduced to form metallic silver and chloride ion. The silver chloride cathode shares many of the qualities of the silver anode, with some additional desirable traits No electrolyte is depleted by its reaction it is hydrophilic and therefore wetted by the reservoir electrolyte and the insoluble reaction product, metallic silver, is electrically conductive, eliminating problems of polarization or isolation of the redox species. Because of this combination of properties, the operating voltage of silver chloride decreases with use, and the utilization of a silver chloride cathode is nearly 100%. 

Because of technological advances in this area, much higher efficiency polarizers and detector systems are available today than had been in recent years. One example of this is the commercial availability of infrared wire grid polarizers (Perkin Elmer) which is of higher efficiency in transmission and polarization than the former Brewster plate silver chloride polarizers. 

Neither of the two earlier reviews on the infrared spectroscopy of carbohydrates " dealt with the uses of plane-polarized radiation. This is, no doubt, attributable to the fact that both reviews were principally concerned with crystalline sugars, for which few such spectra are available. However, the polarized infrared spectra of such polysaccharides as cellulose, chitin, and xylans, in the form of oriented films, have been measured " and have provided information that other techniques could not give. It is, therefore, desirable that a brief discussion should be here provided of both the experimental and the interpretational aspects (see p. 28) for a detailed discussion, the reader is referred elsewhere. The commonest method of obtaining polarized infrared radiation is with a transmission polarizer (rather than a reflection polarizer). Selenium film and silver chloride sheet have both been used of these, the latter is the more popular because it is the more robust. A stack of about six sheets, each about 50-100 m thick, is... 

To obtain a beam of polarized infrared radiation one can use silver chloride (Newman and Halford, 1948) or selenium (Elliott et ai, 1948a) polarizers. Several plates of silver chloride or a thin film of selenium are tilted at the polarizing angle relative to the unpolarized infrared beam of radiation. Figure 3.28 (Colthup et ai, 1964) describes the optical effects in schematic fashion. 

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