Tungsten light

The electrical uses of mercury include its application as a seal to exclude air when tungsten light bulb filaments are manufactured. Fluorescent light tubes and mercury arc lamps that are used for street lighting and as germicidal lamps also contain mercury. 

High-intensity radiation in the visible region of the spectrum is obtained from a simple tungsten light bulb. This bulb is essentially a black-body emitter and the relative intensity of the wavelengths of light emitted depends on the temperature of the tungsten wire as shown below. 

The aryldiazosulphide ArN=NSPh (1.3 mmol) in DMSO (50 ml) is stirred under Ar with TBA-CN (1.75 g, 6.5 mmol) in DMSO (50 ml) and the solution is irradiated with tungsten light until the evolution of N2 ceases. Brine (150 ml) is added and the mixture is extracted with EtzO (4 x 50 ml). The ethereal extracts are washed with aqueous NaOH (10%, 50 ml) and brine (50 ml), dried (Na2S04), and evaporated to yield the benzonitrile (30-70%). The diazosulphides are potentially EXPLOSIVE. 

Fig. 7. Conversion curve (arbitrary unit) for polymerization of methyl methacrylate in toluene solution on the presence of triethylaluminum at 256° K in darkness and illuminated with 100 W tungsten light (Aixen and Casey [43))...

The hardening bath is a violet blue color by tungsten light when freshly mixed but turns to yellow-green with use it then ceases to harden and should be replaced with a fresh bath. The hardening bath should never be overworked. An unused bath will keep indefinitely, but a partially used bath will deteriorate rapidly within a few days. 

The set-up used consists of a tungsten light source (20 W, 12 V), optical Y-fibre couplers (PMAA, 1 mm core diameter, microparts, Dortmund, Germany) and a diode array spectrometer (MMS, Zeiss, Jena, Germany). Interference spectra were recorded from 450-700 nm. 

Figure 2 Effects of bleaching by tungsten light upon absorption induced by two hours x-irradiation in graphite-reduced glass containing 0.1% Fe. Curve 1) Original absorption. (Curve 2) Absorption remaining after eight minutes exposure to intense tungsten source. Source From Ref. 4.

A tungsten light source does not supply sufficient radiant energy for measurements below 320 nm. In the UV region of the spectrum, a low-pressure mercury-vapor lamp that emits a discontinuous or line spectrum is useful for calibration purposes but is not very practical for absorbance measurements, because it can be used only at certain wavelengths. Hydrogen and deuterium lamps provide sources of continuous spectra in the UV region with some sharp emission... 

Scheme 11.4 illustrates some representative halogenation reactions. The reaction in Entry 1 was conducted by slow addition of bromine to excess 2-methylpentane at 60°C, with irradiation from a tungsten light bulb. The reaction in Entry 2 is a typical benzylic bromination, carried out at 125°C with irradiation from a sun lamp. Entries 3 and 4 are examples of NBS bromination using benzoyl peroxide as the initiator. Entry 3 is interesting in that none of the allylic isomer 2-bromo-3-heptene is found. Entries 5 and 6 are examples of chlorination by f-butyl hypochlorite in which the f-butoxy radical is the chain carrier. Note that in Entry 6, both the primary and secondary allylic products are formed. The reaction in Entry 7 uses sulfuryl chloride as the halogenation reagent. Note that in contrast to chlorination with CI2 (see p. 1021), the reaction shows selectivity for the benzylic position. 

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