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- Author or Editor: Farn P. Parungo x
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Abstract
Experiments of ice nucleation by silver iodide were conducted in a cold chamber at various temperatures. The seeded ice crystals were replicated and an examination of the position of AgI nuclei in individual ice crystals was made using an electron microscope. The mechanism of ice nucleation is discussed.
Abstract
Experiments of ice nucleation by silver iodide were conducted in a cold chamber at various temperatures. The seeded ice crystals were replicated and an examination of the position of AgI nuclei in individual ice crystals was made using an electron microscope. The mechanism of ice nucleation is discussed.
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Abstract
The ice nucleating ability of a series of substituted phenols and benzoic acids was determined. Two different measures of activity were utilized: the onset temperature of freezing, as determined on a cold stage microscope; and the relative number of ice nuclei formed at a fixed temperature in a cold chamber. Reactivity was generally found to vary with the potential strength of a hydrogen bond between the hydroxyl or carboxyl group and a water molecule. In a given series of compounds (i.e., either the phenols or the benzoic acids), it was found that the onset temperature could be predicted from the sigma value of Hammett for the individual substituent, so long as the substituent was in the meta and para position, and was not more strongly hydrogen bonding than the functional group of the parent compound. This suggests a free-energy relationship between molecular structure and nucleating power. These observations are offered for further discussion; it is clearly premature to offer a detailed mechanism for the effect.
Abstract
The ice nucleating ability of a series of substituted phenols and benzoic acids was determined. Two different measures of activity were utilized: the onset temperature of freezing, as determined on a cold stage microscope; and the relative number of ice nuclei formed at a fixed temperature in a cold chamber. Reactivity was generally found to vary with the potential strength of a hydrogen bond between the hydroxyl or carboxyl group and a water molecule. In a given series of compounds (i.e., either the phenols or the benzoic acids), it was found that the onset temperature could be predicted from the sigma value of Hammett for the individual substituent, so long as the substituent was in the meta and para position, and was not more strongly hydrogen bonding than the functional group of the parent compound. This suggests a free-energy relationship between molecular structure and nucleating power. These observations are offered for further discussion; it is clearly premature to offer a detailed mechanism for the effect.
Abstract
The authors' recent studies on phenols and benzoic adds suggest that the ability of solid organic compounds to nucleate freezing of supercooled water may be predicted, at least in a limited number of cases, from purely thermodynamic considerations. A report that pure, optically active amino acids nucleate freezing at temperatures different from their inactive forms suggests that a quantitative study of the differences might be revealing.
It was found that differences in nucleation temperature were related in a linear manner to differences in heat of solution of active and racemic forms. Tyrosine is an exception to the above behavior. It is suggested that nucleation on one of the forms may occur at the phenolic group.
Abstract
The authors' recent studies on phenols and benzoic adds suggest that the ability of solid organic compounds to nucleate freezing of supercooled water may be predicted, at least in a limited number of cases, from purely thermodynamic considerations. A report that pure, optically active amino acids nucleate freezing at temperatures different from their inactive forms suggests that a quantitative study of the differences might be revealing.
It was found that differences in nucleation temperature were related in a linear manner to differences in heat of solution of active and racemic forms. Tyrosine is an exception to the above behavior. It is suggested that nucleation on one of the forms may occur at the phenolic group.
Abstract
Results from measurements made to study the behavior of lead aerosols in Denver urban air as latent ice nuclei are discussed.
In the study, use was made of three independent measuring systems. These were: 1) an NCAR continuous ice nucleus counter with a capability to convert suspended lead compounds to lead iodide particles prior to passage through the cloud chamber and counting unit, 2) an atomic absorption spectrophotometer for analysis of lead content in collected air and rain water samples, and 3) the use of Tufts’ spot test for obtaining lead particle concentration and size distribution from collected Millipore filters. Both ground and airborne measurements were made.
Pertinent findings included: 1) good Qualitative agreement among the three types of measurements; 2) lead content of rain water an order of magnitude greater than silver concentration in seeded snow samples which were collected in a weather modification seeding target area using silver iodide as the seeding agent; and 3) 10-300 lead particles (latent ice nuclei) liter−1 existing up to 9000 ft above the surface when unstable temperature stratification existed and which were converted into active ice nuclei (lead iodide particles) when passed through an iodine vapor chamber.
Abstract
Results from measurements made to study the behavior of lead aerosols in Denver urban air as latent ice nuclei are discussed.
In the study, use was made of three independent measuring systems. These were: 1) an NCAR continuous ice nucleus counter with a capability to convert suspended lead compounds to lead iodide particles prior to passage through the cloud chamber and counting unit, 2) an atomic absorption spectrophotometer for analysis of lead content in collected air and rain water samples, and 3) the use of Tufts’ spot test for obtaining lead particle concentration and size distribution from collected Millipore filters. Both ground and airborne measurements were made.
Pertinent findings included: 1) good Qualitative agreement among the three types of measurements; 2) lead content of rain water an order of magnitude greater than silver concentration in seeded snow samples which were collected in a weather modification seeding target area using silver iodide as the seeding agent; and 3) 10-300 lead particles (latent ice nuclei) liter−1 existing up to 9000 ft above the surface when unstable temperature stratification existed and which were converted into active ice nuclei (lead iodide particles) when passed through an iodine vapor chamber.
Abstract
A procedure is presented for identifying those silver iodide particles in ice crystals that have behaved as snow crystal nuclei. The new technique is based on the principle that any submicron particle can act as a nucleus in its own superstaurated solution, and can grow to any desired crystal size (the final size depending on time of exposure to the supersaturated solution). For the procedure presented here, an aqueous solution of 30% potassium iodide supersaturated with silver iodide is used.
Application of the technique in a weather modification field research project is described. A case-study example is presented, and results of the season's experiments are discussed with emphasis on contributions of the nuclei identification data. It is concluded that the technique has considerable practical utility in qualitative determination of effects from cloud seeding.
Abstract
A procedure is presented for identifying those silver iodide particles in ice crystals that have behaved as snow crystal nuclei. The new technique is based on the principle that any submicron particle can act as a nucleus in its own superstaurated solution, and can grow to any desired crystal size (the final size depending on time of exposure to the supersaturated solution). For the procedure presented here, an aqueous solution of 30% potassium iodide supersaturated with silver iodide is used.
Application of the technique in a weather modification field research project is described. A case-study example is presented, and results of the season's experiments are discussed with emphasis on contributions of the nuclei identification data. It is concluded that the technique has considerable practical utility in qualitative determination of effects from cloud seeding.
