Manometric methods, vapor pressure

Carbon was estimated by a variation of the Van Slyke method.(2) A 30-100 mg sample was heated for 30 minutes with 0.5 g K2Cr207, lg KIOj, 10 mL 20% fuming H2S01( and 5 mL HjPO in a closed flask swept by a purified N2 stream. The N2 stream carried the evolved C02 to an absorption solution of 0.5M Na0H-0.3M N H. After the wet combustion, the absorbed C02 was released from an aliquot of the NaOH solution with lactic acid in a manometric apparatus. Corrections were applied for the vapor pressure of water and for reagent blank. 

Milton et al. [1.136] used this methods and refer to it as manometric temperature measurement. They used times of pressure rises of up to 30 s. During this time, the ice temperature will increase, mainly due to continued heat flow. Therefore, an equation has been developed to transform the experimental pressure data, including three other corrections, into the true vapor pressure of the ice. If the valve is closed for only a very short time, < 3 s, and the pressure is measured and documented 60 to 100 times/s, these data can be recorded as shown in Fig. 1.78.1. The automatic pressure rise measurements (1) can then be plotted... 

A2.1 Factors to Consider When Estimating Water Vapor Pressure A2.2 Dew-Point Method for the Determination of Water Activity A2.3 Measurement of Water Activity Using Isopiestic Method A2.4 Direct Manometric Determination of Vapor Pressure A2.5 Measurement of Water Activity by Electronic Sensors... 

Manometric method eonsists of thermostating with a high precision (0.0IK) and vapor pressure measurement by a level of mercury with the help of a cathetometer or membrane zero-manometer. The aeeuraey of measurement is 0.1-0.2 mm Hg. 

Miscellaneous methods. Some other techniques, such as dielectric constant measurements , conductimetry , mass spectrometry , and electronic spectroscopy are used less frequently but can also be useful. Change in vapor pressure determined with a manometric device can be used when the reaction mixture contains a volatile compound such as ethylene oxide... 

Different test methods are used to conduct permeability behaviors of plastics to measure gas, water, and other material vapor permeability. Permeability test procedures used to measure the permeability of plastic films include those identified as the absolute pressure method, the isostatic method, and the quasi-isostatic method. Basic approach mounts a plastic film sample between two cell chambers of a permeability cell (two piece closed container). One chamber holds the gas or vapor to be used as the permeant. The permeant then diffuses through the film into a second chamber, where a detection method such as optical devices, infrared spectroscopy, a manometric, gravimetric, or coulometric method isotopic counting or gas-liquid chromatography provides a quantitative measurement. 

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