Gas burette

The air may be collected directly into a Hempel gas-burette (Fig. 76) and there measured. This burette consists of a glass tube H calibrated in ml. from the tap E downwards, and connected by a piece of rubber tubing to the reservoir R, the height of which can be adjusted. The tap E is a 3-way tap. by which the tube H can be connected directly through to the capillary tube above, or either tube can be connected through the left- hand end of the tap to the atmosphere. 

Methods of EGA using selective sorption, condensation of effluent gases, infrared absorption and thermoparticulate analysis have been reviewed by Lodding [144]. The use of simple gas burette systems should not be forgotten and an Orsat gas analysis apparatus can provide useful measurements in studies of the decomposition of formates [169]. Problems have been encountered in the determination of water released Kiss et al. [170—172] have measured the formation of this compound from infrared analyses of the acetylene evolved following reaction of water with calcium carbide. Kinetic data may be obtained by wet methods ammonia, determined by titration after absorption in an aqueous solution, has been used to measure a—time values for the decomposition of ammonium salts in a fluidized bed [173],... 

A recent stndy (13,27) describes the use of Co-Si-TUD-1 for the liquid-phase oxidation of cyclohexane. Several other metals were tested as well. TBHP (tert-butyl hydroperoxide) was used as an oxidant and the reactions were carried out at 70°C. Oxidation of cyclohexane was carried out using 20 ml of a mixture of cyclohexane, 35mol% TBHP and 1 g of chlorobenzene as internal standard, in combination with the catalyst (0.1 mmol of active metal pretreated overnight at 180°C). Identification of the products was carried out using GC-MS. The concentration of carboxylic side products was determined by GC analysis from separate samples after conversion into the respective methyl esters. Evolution and consumption of molecular oxygen was monitored volumetrically with an attached gas burette. All mass balances were 92% or better. 

Low-pressure hydrogenation apparatus fitted with a gas burette system to measure the hydrogen consumed1361... 

The Schlenk tube was connected to a low-pressure hydrogenation apparatus fitted with a gas burette system to measure the hydrogen consumed. The Schlenk tube was flushed through three cycles (reduced pressure/ hydrogen) and then placed under an atmospheric pressure of hydrogen. The burette was filled with 200 mL of hydrogen. 

Method 4 Na2S.9H20 (2.65 g, 11 mmol) in H20 (10 ml) is added the dibromoalkane (5 mmol) and Aliquat or TEBA-C1 (0.5 mmol) in PhH (10 ml). The initially exothermic reaction is stirred for ca. 1 h at room temperature and the organic phase is then separated, washed with H20 (2 x 20 ml), dried (MgS04), and evaporated to yield the alkene. Gaseous alkenes are collected using a gas burette ( the solvent can be omitted with liquid dihaloalkanes). 

An alternative method of obtaining the gas evolution rate is to use an open test, venting to a constant pressure automated gas burette or to a thermal mass flowmeter111. However, these techniques have been developed to characterise the normal chemical reaction by measuring gas flow rates from a heat flow calorimeter... 

The sample tube and gas burette are evacuated and then a nonadsorbing gas — frequently helium —is introduced into the gas burette. The burette is graduated with respect to volume and also serves as one leg of a manometer so that both the volume and pressure of gas in the burette can be measured. Ambient temperature is assumed to apply throughout. 

The three-way stopcock is opened to connect the gas burette with the sample tube. The new pressure and volume are read. From this, the volume of the dead space — the volume beyond the three-way stopcock that is not occupied by sample —can be determined (see Example 9.1). 

EXAMPLE 9.1 Construction of Adsorption Isotherms The following pressure-volume (p-V) data were collected at a temperature of 22°C. The l/ s are volumes in the gas burette, and the numerical subscripts refer to the steps itemized above. 

The gas burette should itself be thermostated unless the laboratory has very good temperature control. 

Add to the flask D, exactly 5 ml of ceric ammonium sulfate from the burette A, lower the bulb G to the vicinity of the 30 ml mark °f the gas burette E. Shake the flask D(to-S her with the clamp and stand) vigorously... 

Zinc is determined quantitatively by titration of the acid solubilized material with K ferro-cyanide, the endpoint being indicated when a drop of uranyl nitrate produces on a porcelain plate a brown tinge with a drop of titrated mixt. Metallic Zn is determined by the hydrogen evolution method using a gas burette (Ref 8)... 

Figure 1-2 Schematic diagram of a Victor Meyer apparatus for determination of the vapor density of a substance that is volatile at the oven temperature 7V The air displaced from the heated chamber by the volatilization of the sample In the bulb is measured in the gas burette at temperature 72 as the difference in the burette readings V2 and V,.

In the AOAC procedure, a container s cap is punctured with a strong needle. The gas is then shaken out of the product and collected in a gas burette. The pressure is finally adjusted to atmospheric before the volume is read off the burette. Carbon dioxide can also be removed by dissolving it in sodium hydroxide solution any other gases in the container can also be measured in this way. 

For precise determination of the amount of the condensed gas, the container should be weighed before and after the gas is condensed. For gases which are not easily condensed, the volume can be measured using a calibrated gas burette of the type shown in Fig. 2.63(a) and the gas then allowed to pass gradually into the flask after suitable drying or other purification. 

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