Cloud apparatus

Fig. 1. Schematic diagram of the laser-excited diffusion cloud apparatus.

Several instniments have been developed for measuring kinetics at temperatures below that of liquid nitrogen [81]. Liquid helium cooled drift tubes and ion traps have been employed, but this apparatus is of limited use since most gases freeze at temperatures below about 80 K. Molecules can be maintained in the gas phase at low temperatures in a free jet expansion. The CRESU apparatus (acronym for the French translation of reaction kinetics at supersonic conditions) uses a Laval nozzle expansion to obtain temperatures of 8-160 K. The merged ion beam and molecular beam apparatus are described above. These teclmiques have provided important infonnation on reactions pertinent to interstellar-cloud chemistry as well as the temperature dependence of reactions in a regime not otherwise accessible. In particular, infonnation on ion-molecule collision rates as a ftmction of temperature has proven valuable m refining theoretical calculations. 

The VIRTIS apparatus (Visible Infrared Thermal Imaging Spectrometer) on board can observe the atmosphere and the cloud layers at various depths (on both the day and the night side of the planet). VIRTIS has also provided data for the first temperature map of the hot Venusian surface. These data have led to the identification of hot spots and thus provided evidence for possible volcanic activity (www.esa.int/specials/venusexpress). 

Laser diffraction is a fast alternative for analysis of the size distribution of particles in an aerosol cloud. The theory of laser diffraction is well understood [124,125]) but this technique requires special measures to test inhalation devices and to interpret the results correctly. One of the major problems is that flow adjustment through the inhaler is not possible. Furthermore, the presence of carrier particles from adhesive mixtures may disturb the measurement of the fine drug particles and the size distribution obtained is of an unknown dehvered mass fraction of the dose. These practical problems and limitations have been solved by the design of a new modular inhaler adapter for the Sympatec laser diffraction apparatus (Figure 3.6). 

The foregoing expression applies only to ions at a concentration approaching 0 and in a nonconductive solvent. Polyionic molecules are surrounded by a cloud of counterions that alter the effective electric field applied on the ions to be separated. This renders the previous expression a poor approximation of what really happens in an electrophoretic apparatus. 

These observations could be reconciled with the extensive work on the interaction of N02 with bulk solutions if reaction (12) is much faster at the interface than in the bulk. The existence of such an enhanced reaction is also suggested by work using a falling-drop-let apparatus (Ponche et al., 1993) and cloud and smog chambers discussed in the following section, where the reaction order in N02 was measured to be one, rather than two as in the bulk-phase reaction. 

A versatile apparatus for determining minimum energies for electric-spark ignition of gases and dust clouds, developed by Blanc et al (Ref 1), is shown below... 

Distillation of Ether over Metallic Sodium. Do not distil the liquid to the end ) Assemble the apparatus (Fig. 20). Put 5-10 g of metallic sodium dried with filter paper, cleaned of its oxide film, and cut up into pieces (about 5x5 mm in size) and 300 ml of ether into the flask. Connect a cooler with a receiver to the flask with the ether. Heat the distillation flask on a water hath placed on an electric stove with an enclosed coil. The distilled ether in contact with freshly cut lustrous metallic sodium should produce a faint cloud of hydrogen bubbles. 

For a large gas release, the areas in the path of the cloud may well have to be evacuated. Workers sent in to make repairs or assess damage should be equipped with air-tight, acid-proof clothing and a self-contained breathing apparatus. 

Interfacial mass transfer of trace gases into aqueous pnase is investigated in a UV absorption-stop flow apparatus. For the first time, the mass accommodation coefficients are determined for O3 (5.3x10" ) and for SO2 (>2x10 2) The results are incorporated into a simple model considering the coupled interfacial mass transfer and aqueous chemistry in cloud drops. It is shown that dissolution of O3 into a drop is fast compared with its subsequent oxidation of dissolved S02 In addition, the conversion rate of S(IV) to S(VI) in aqueous drops by ozone reactions is not limited by interfacial resistance. 

Recalling Chapter 1, explosion protection in the presence of combustible dusts (stirred-up dusts as a cloud or dust layers/deposits on the surface of an electrical apparatus) requires ... 

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