Ultraviolet light lamps

Ultraviolet light sources are based on the mercury vapor arc. The mercury is enclosed ia a quart2 tube and a potential is appHed to electrodes at either end of the tube. The electrodes can be of iron, tungsten, or other metals and the pressure ia a mercury vapor lamp may range from less than 0.1 to >1 MPa (<1 to >10 atm). As the mercury pressure and lamp operating temperatures are iacreased, the radiation becomes more iatense and the width of the emission lines iacreases (17). 

Lighting. An important appHcation of clear fused quartz is as envelop material for mercury vapor lamps (228). In addition to resistance to deformation at operating temperatures and pressures, fused quartz offers ultraviolet transmission to permit color correction. Color is corrected by coating the iaside of the outer envelope of the mercury vapor lamp with phosphor (see Luminescent materials). Ultraviolet light from the arc passes through the fused quartz envelope and excites the phosphor, produciag a color nearer the red end of the spectmm (229). A more recent improvement is the iacorporation of metal haHdes ia the lamp (230,231). 

Chlorine free radicals used for the substitutioa reactioa are obtaiaed by either thermal, photochemical, or chemical means. The thermal method requites temperatures of at least 250°C to iaitiate decomposition of the diatomic chlorine molecules iato chlorine radicals. The large reaction exotherm demands close temperature control by cooling or dilution, although adiabatic reactors with an appropriate diluent are commonly used ia iadustrial processes. Thermal chlorination is iaexpeasive and less sensitive to inhibition than the photochemical process. Mercury arc lamps are the usual source of ultraviolet light for photochemical processes furnishing wavelengths from 300—500 nm. 

Instruments for the measurement of fluorescence are known as fluorimeters or spectrofluorimeters. The essential parts of a simple fluorimeter are shown in Fig. 18.1. The light from a mercury-vapour lamp (or other source of ultraviolet light) is passed through a condensing lens, a primary filter (to permit the light band required for excitation to pass), a sample container, a secondary filter (selected to absorb the primary radiant energy but transmit the fluorescent... 

Never view the flame or hollow cathode lamps directly protective eye wear should always be worn. Safety spectacles will usually provide adequate protection from ultraviolet light, and will also provide protection for the eyes in the event of the apparatus being shattered by an explosion. 

Thin-layer plates were made with silica gel-calcium sulfate and each contained a mixture of zinc silicate and zinc cadmium sulfide as phosphors. Separated components are generally visible under ultraviolet light by fluorescence quenching. This was true, in part, for the pyrethrins, except that some of the separated components possessed a natural fluorescence under the ultraviolet lamps. 

Nalidixic acid Take this drug with food to prevent GI upset. Avoid prolonged exposure to sunlight or ultraviolet light (tanning beds or lamps) because an exaggerated sunburn may occur. 

It is advisable to wrap the entire apparatus with aluminum foil to avoid exposure to ultraviolet light. The reaction solution can be observed through a small hole in the aluminum foil which is shielded from the direct radiation of the lamp. 

Prepare Van Urk reagent by adding 0.5 g p-dimethylamino-benzaldehyde, 100 ml water, 100 ml concentrated sulfuric acid. Dissolve 1 mg substance in 1 ml ethanol and mix with 2 ml Van Urk reagent and illuminate for 10 minutes with an ultraviolet lamp (black light). Psilocin gives a blue-grey, psilocybin a red-brown color. 

Under similar conditions, cw-azobenzene could be oxidized to cw-azoxy-benzene. Evidently the only major precaution to be taken in this preparation is the exclusion of ultraviolet light (by carrying the reaction out in a dark room) [24]. Whether this precaution is truly required is open to some doubt since cis-azoxybenzenes were prepared more recently by oxidation while warming with a heating lamp [28]. The isomerization by ultraviolet light is probably an equilibrium process in which equilibrium constants have a pronounced dependence on the chemical constitution of the materials involved. Therefore variations in the observations of the stability of the products are not entirely surprising. 

The use to which the machine will be put has a bearing on its choice. If it is used for sheets, films, or surface treatment, where only modest penetration, is called for, a low voltage machine, such as the ICT, is suitable. If greater penetration is necessary, a higher voltage machine is needed, and the choice is between the resonant transformer and the Dynamitron. For surface treatment, an ultraviolet light might be sufficient. This is created when an electric arc passes between electrodes separated by gas or vapor. There are two main classes of arcs open, such as the carbon arc, and closed as the various vapor lamps. 

An ultraviolet detector using a flow cell such as that. in Figure 25-19 is the most common HPLC detector, because many solutes absorb ultraviolet light. Simple systems employ the intense 254-nm emission of a mercury lamp. More versatile instruments have deuterium, xenon, or tungsten lamps and a monochromator, so you can choose the optimum ultraviolet... 

Photolysis is carried out in an 850-ml. Pyrex glass vessel equipped with a water-cooled quartz probe. The ultraviolet light source is a 450-watt lamp with a Vycor filterf. To reduce the dangers from a possible explosion or eye damage from ultraviolet radiation, the reaction vessel shown in Fig. 5 is contained in a wooden box. 

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