Re-evaporation

The temperature at which this reaction is canied out is limited by considerations of the possibility of re-evaporation of As2 molecules and gallium atoms from the GaAs him. The semiconduchng compounds are less susceptible to this problem than the separate elements because of the thermodynamic stabilities of diese compounds, as discussed above. 

Nacb-verdampfung, /. re-evaporation, -ver-gasung, /. aftergasification. -verseifung, /. aftersaponification, -vulkanisation, f. aftervulcanization, aftercure. 

Where dust control is important the system should only be used with a supply of demineralized water to avoid solids being passed into the conditioned space. The temperature of the air must be sufficient to hold the quantity of moisture being supplied, any excess being deposited in the duct. Unless drained away, this can give rise to corrosion and to incorrect control by re-evaporation when the humidifier is switched off under control. 

Alloys of high nickel content also have improved chloride stress-corrosion cracking resistance and Incolloy 825 has replaced type 321 stainless steel for steam bellows on some plants. Occasionally cracking of the latter was experienced due to chloride-contaminated steam condensing in the convolutions on shut-down and being re-evaporated at start-up. 

Subsurface runoff. When precipitation hits the land surface, the vast majority does not go directly into the network of streams and rivers in fact, it may be cycled several times before ever reaching a river and the ocean. Instead, most precipitation that is not intercepted by the vegetation canopy and re-evaporated infiltrates into the soil, where it may reside as soil moisture, percolate down to ground-water, or be transpired by plants. 

However, a final experiment, using a more concentrated dichromate filter, indicated that we may be able to improve our results considerably. In this event it is expected to compare the properties of the two types of iodine and to measure the rate at which equilibrium between the two is restored. Some qualitative experiments along this line, which need to be confirmed, indicate that equilibrium is restored rather slowly and several days at least are required. Condensation and re-evaporation of the iodine does not seem to hasten the attainment of equilibrium appreciably, indicating the persistence of the two molecular forms in the solid state. 

The same percentage of the chloride will be precipitated on re-evaporation. 

An early CO distillation pilot plant described by Johns (in London (1961), reading list), used a two section vacuum insulated column packed with wire gauze rings. The upper section was 5.2 m long with a diameter of 3.2cm, the lower 4.6 m x 1.9 cm. The column contained about 600 plates. An intermediate boiler re-evaporated part of the downward flowing liquid at the junction. This plant accumulates product in the liquid and enriches toward the bottom. Enriched CO (0.4 g day-1 of 65% 13C and 0.05 g day-1 of 5% lsO) was withdrawn from the bottom... 

If we assume an equal probability for all adsorbed molecules to evaporate we can readily calculate the average life of a molecule on the surface between the acts of condensation and re-evaporation from the rate of condensation and the amount of surface covered. Such calculations have been made by Langmuir J.A.G.S. XL. 1393, 1918) who gives the following data for the mean length of life in... 

In the case of the adsorbed molecules a certain number of these as we have seen are capable of re-evaporating. If E be the energy... 

One of two things may then happen. After a time they may re-evaporate. This depends upon their acquiring sufficient kinetic energy to carry them beyond the range of attraction of the surface forces. Escape may be rendered easier at certain times if the attractive force passes periodically through a minimum value as a result of... 

Suspend the purified salt in 850 ml of water in a stoppered bottle, add 25 ml of pure pyridine and shake the mixture for 4-5 hours. Remove the insoluble pyridine rhodanilate by filtration and wash it with 100 ml of cold water (2). Combine the pale pink filtrate and washings, and add glacial acetic acid dropwise until the formation of a small pink precipitate is complete. Filter, evaporate the almost colourless filtrate to dryness (rotary evaporator) and suspend the residue in absolute ethanol and re-evaporate twice. Dry the resulting faintly pink crude proline in a vacuum desiccator over silica gel the yield is about 18 g. Recrystallise from the minimum volume of absolute ethanol to obtain 11 g (7.3% based on gelatin) of L-proline, m.p. 218-219 °C (decomp.), [oc]d8 —85.6° (c3.0 in H20). Check the purity of the product by t.l.c. on silica gel using the solvent system butan-l-ol-acetic acid-water, 4 1 1 Rf 0.26 (yellow spot with ninhydrin). 

Figure 4.2 shows the concentration of HTO in rainfall, in TU units, at Valentia on the southwest coast of Ireland from 1952 to 1972 (Weiss et al., 1979). Measurements at sea showed no difference in TU of rain and water vapour, when allowance was made for the isotopic difference in vapour pressure of HTO and H20. TU levels in water vapour and rain are higher well inland than at the coast by factors up to four (Eriksson, 1965). There are two reasons for this difference. The rainfall and humidity are usually less in continental areas, so that the downwards flux of HTO is less diluted with H20. Also, re-evaporation of HTO from land increases the atmospheric concentration at low levels. 

For the deposition of particles, bounce-off and blow-off, which must be carefully distinguished, may be considered analogous to the accommodation coefficient and to re-evaporation respectively. 

For coniferous forests, the calculated v+ increases rapidly as droplet diameter increases to 10 /iva. Also, w is typically several times greater over a forest than over grassland, so the disparity is greater in terms of vt. Lovett Reiners (1986) found vt of cloud droplets to a subalpine fir forest to be 300 mm s-1, increasing possibly to 2000 mm s-1 on the lee side of gaps in the canopy. In these conditions, occult precipitation is the equivalent of 0.1 to 0.3 mm h-1 of rainfall (Lovett, 1984). Much of the intercepted water re-evaporates, but ions dissolved in the droplets remain on the leaves and are potentially damaging. 

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