Low-pressure Mercury Vapor Lamp Research Articles

Etude comparative de la degradation de quelques molecules aromatiques simples en solution aqueuse par photolyse UV et par photolyse du peroxyde d'hydrogene

Abstract The photooxidation of some chloroaromatic and nitroaromatic compounds (chlorobenzenes, nitrobenzenes) in water by UV radiation and UV radiation in the presence of hydrogen peroxide was studied. Diluted aqueous solutions of organic compounds (10‐4 mol l‐1) were irradiated at pH 7.5 and at 16°C in a closed reactor equiped with a low pressure mercury vapor lamp. The results showed that chlorobenzenes are more rapidly photodecomposed than nitroaromatic compounds and the rates of degradation were greatly increased by addition of hydrogen peroxide (10‐3 mol l‐1). The degradation pathway of aromatic compounds in the presence of hydrogen peroxide and UV light leads to the production of hydroxylated derivatives (phenolic compounds) as intermediates and chloride, nitrate and carbon dioxide as oxidation end‐products. The effects of benzene ring substituents (Cl, NO2, OH) on the oxidation rate of aromatic compounds by H2O2/UV and the influence of the UV absorbance of the irradiated solutions at 253.7 nm on t...

Relation between photoacoustic amplitude and quenching of mercury3P1→1S0fluorescence by hydrogen in argon

The quenching of mercury fluorescence excited by a modulated low-pressure mercury vapour lamp causes sound to be developed in the quench gas. Apparatus has been developed which allows the simultaneous measurement of fluorescence and acoustic signals as a function of quench gas composition. The amplitudes of the fluorescence and acoustic signals sum to a constant over the range of quench gas compositions from 0.01 to ca 1%, by volume, of hydrogen in argon. Normalized amplitudes therefore sum to unity. Similar results are also obtained by substituting helium for argon. The normalized amplitude of the acoustic signal is related to quench gas composition by a modified Stern–Volmer equation. Provisional quench reaction rate constants obtained from acoustic data at 295 K, using this equation, compare well with rate constants obtained from fluorescence data and also with literature values.

Zur Vergrauung von Entladungsgefäßen

Vitreous discharge tubes for low-pressure mercury vapor lamps will display after about 1000 hrs of operation a greyish appearance which increases with time. Said darkening can be simulated within a short period of time by applying an electric field transverse to the discharge. The transverse field causes migration of sodium ions of the glass towards the discharge. These ions migrate to the inner surface of the glass where they amalgamate.

Photochemical Dechlorination of Water Supply for Fish Tanks, with Commercial Water Sterilizers

Commercial mercury-lamp water sterilizers can be used for removal of free chlorine in water supplies, by photochemical action. The efficiency of removal decreases with increasing pH, but is little affected by temperature. It is greatest at low initial chlorine concentration. Equipment with either low or high pressure mercury vapor lamps may be used. Removal of 90% of free chlorine can be effected at about 13.0 liters min−1 with a sterilizer using eight low pressure lamps of 40 W, or at 50 liters min−1 or more with two 1200-W sterilizers with high pressure lamps in tandem. Treated water appears to be harmless to fish.

Photosensitised interaction of acetylene and hydrogen sulphide

Varying pressures of hydrogen sulphide and acetylene have been irradiated separately and together with the light from a low-pressure mercury vapour lamp. The HS radicals produced in the direct photolysis have been shown to add to acetylene to form HSCHCH˙, the process being reversible with a negative energy of activation. Ethenethiol is produced by the abstraction of hydrogen from hydrogen sulphide by this radical. A rapid polymerisation of ethenethiol occurs and the resulting polymer has been shown to have the general formula (C2H4S)n by elemental analysis and mass spectrometry. The effects of variation of experimental parameters on the progress of these reactions are discussed.

Photometric scanning of a centrifuged gradient column at several wavelengths

Centrifuged density gradient columns are often analyzed by pumping or dripping the contents through a flow cell to measure and record the absorbance as a function of depth (4, 7). The absorbance is usually measured at 253.6 mμ, since light of this wavelength is easily obtained from a low-pressure mercury vapor lamp. Density gradient columns are not destroyed by flow through a channel, provided that the path does not force a density inversion. The path must be continuously upward if the gradient is pumped out of the top of the tube, and downward if the gradient is removed from the bottom of the tube. In a smooth tube gradient columns may be repeatedly pumped up and down with little effect on the gradient or a virus zone (5). We report here on a flow cell with a reservoir on top for collection of the centrifuged gradient column after it has been pumped through the flow cell. The flow cell fits in the sample chamber of a recording spectrophotometer. The gradient column can be pumped up and down through the flow cell several times while the absorbance is recorded at a different wavelength each time.

Precipitation from homogeneous solution by photochemical action: Determination of thorium

Thorium was precipitated from homogeneous solution by photochemical reduction of periodate to iodate in a solution containing thorium and perchloric acid, by means of a 2537 Å low-pressure mercury vapour lamp. For weighing, the precipitate was redissolved, precipitated once as thorium hydroxide, and finally as thorium oxalate, which was ignited to thorium dioxide. Quantitative results were obtained in the range 35–180 mg of thorium.

Photolytic Degradation of Textile Fibres in the Far Ultra-violet

ALTHOUGH it is generally recognized that the action of far ultra-violet radiation on textile fibres is photolytic in character, investigations of the influence of oxygen and water vapour on the complex reactions involved have been mainly confined to cotton cellulose. The temperature of the system and the parameter of degradation are other factors which profoundly influence the nature of the results1. In the experiments described here we have used as parameter the loss in tensile strength of the textile yarn which was exposed to the radiations from a low pressure mercury–vapour lamp emitting mainly at 2537 A. The yarn was contained in the inner compartment of a brass cell fitted with a quartz window. The cell was maintained at a constant temperature by circulating a suitable heating (or cooling) medium through the outer compartment. During the experiment a stream of gas brought to the required temperature was passed through the cell. For the exposures (Fig. 1) in dry oxygen and nitrogen involving temperatures down to −60° C the quartz face of the brass cell formed part of the wall of an airtight lamp chamber. At the bottom of the chamber was a tray of phosphorus pentoxide to absorb moisture and prevent the deposition of ice on the cold quartz plate. In addition a stream of dry nitrogen was passed continuously through the chamber. For the experiments (Fig. 2) with dry and moist air in which the lowest temperature was 15° C, this procedure was unnecessary and the cell was irradiated in a large well ventilated cupboard. Where dry gases were used they were dried with phosphorus pentoxide. In experiments performed in air at 100 per cent relative humidity, air was bubbled through a sintered glass filter immersed in distilled water which was maintained at the same temperature as the cell.

Discharge Lamps: Colour, Efficiency and Application

Progress in the efficiency and colour quality of discharge lamps is reviewed. Spectral band histograms give details of the distribution of radiation in sixteen bands covering the near ultraviolet and visible regions. Radiated power in each band combined with the appropriate factor for luminous efficiency of radiation enables the luminous efficiency of each lamp type to be determined. Improvements in the efficiency and colour of discharge lamps is illustrated by similar histograms for high- and low-pressure mercury vapour lamps and experimental high-pressure sodium and mercury iodide discharges. Colour-rendering improvements are assessed by comparing the radiant power histograms with those of natural sunlight and skylight: modern fluorescent lamps duplicate these distributions sufficiently closely in both the visible and near ultra-violet regions to make it practicable to bring lighting of natural quality indoors. The introduction of balanced colour into lighting greatly increases the number of contrasts available. The trend of interior lighting towards the natural standards of daylight and sunlight is considered.

Duration of Phosphorescence II

Phosphorescence of calcite and fluorite, exposed for a few minutes to 2537° ultraviolet light from a low-pressure cold quartz mercury vapor lamp, persisted for 18 years. Emission was detected by placing the phosphorescing minerals on black-and-white and Kodachrome film, to obtain “phosphorographs” of the glowing areas. The rate of emission depends on temperature; the color of the phosphorescence has not changed; these confirm the results of other tests that prove that radioactivity is not involved. The patterns of growth of a crystal, and changes of its environment during formation, are clearly shown by the variegated colors in its phosphorograph.

Ultraviolet sensitivity of fungi associated with mycotic keratitis and other mycoses

Representative spore, hyphal, and yeast phase fungi were exposed to ultraviolet (2537 A) radiation, using the low pressure mercury vapor lamp. The yeast phase was found most susceptible to ultraviolet radiation, and spores the most resistant. Since yeast and hyphae are the phases found in tissue, ultraviolet radiation may be a useful adjunct to antifungal therapy in such diseases as mycotic keratitis.

Corneal ultraviolet phototherapy.

The low-pressure mercury vapor lamp has unique and highly desirable features for corneal ultraviolet phototherapy. The emitted rays are highly germicidal,¹virtually monochromatic at 2,537 A.,1 and totally absorbed by the cornea²with low keratitis effect.³Previous work in corneal ultraviolet phototherapy utilized nonspecific polychromatic radiation which is less germicidal and more toxic than 2,537 A., but good results were still frequently obtained.^4,5The corneal phototherapeutic use of the low-pressure mercury vapor lamp has not been previously reported in the literature. This paper will present: (1) the theoretical basis of corneal ultraviolet phototherapy and the advantages of using this lamp by comparing its only significant spectral radiation, 2,537 A., with the ideal phototherapeutic wavelength, and (2) a clinical and histological study of eyes irradiated by this lamp. <h3>I. Theoretical Basis for Corneal Ultraviolet Phototherapy</h3> The theoretically ideal wavelength for corneal ultraviolet phototherapy should have the following

Photochemistry of Cellulose in the Far Ultra-violet

IT is known that hydrogen, carbon monoxide and carbon dioxide are evolved, and aldehyde and carboxyl groups formed1, during the photolysis of cellulose with short-wave ultra-violet radiation in the absence of oxygen; but the complications produced by the presence of oxygen and water vapour are not fully understood. We have found that temperature markedly affects the nature of the results obtained in atmospheres of dry oxygen and dry nitrogen, and have obtained evidence which suggests that the type of reactions involved are different in oxygen-containing atmospheres in the presence and absence of water vapour. In our experiments we have exposed undyed bleached cotton yarn to the radiations from a low-pressure mercury-vapour lamp emitting mainly at 2537 A. The yarn was contained in the inner compartment of a brass cell fitted with a quartz window. The cell was maintained at a constant temperature by circulating a suitable heating (or cooling) medium through the outer compartment. During the experiment a stream of gas heated to the required temperature was passed through the cell. The degradation of the cotton was assessed by measurements of tensile strength, fluidity (poise−1) in cuprammonium2, reducing power3, and carboxyl content4. Various attempts5 have been made to convert fluidity into degree of polymerization but the accuracy of these relations is doubtful where the cellulose has been subjected to breakdown of largely unknown character. Accordingly, the rise in fluidity of the cotton produced by irradiation has been used as a quantitative measure of the extent of chemical action. A large rise in fluidity corresponds to considerable breakdown of the cellulose molecule.

Intensities of λ1850 and λ2537 in Low-Pressure Mercury Vapor Lamps with Rare Gas Present

The radiant flux in the Hg resonance lines just inside the wall of a lamp with an inside diameter of 35–36 mm is given for currents 0.4−2.0 amp and various bulb temperatures and rare gas fillings. The intensity of the 1850 line ranges from 12 to 34% of that of the 2537 one, with the highest ratios occurring when both arc current and bulb temperature are at the upper end of the ranges used. Since this result is contrary to what one would expect with single-stage excitation of the 1850 line, one must assume that this line is excited mainly by 63P–61P1 transitions when arc current and mercury vapor pressure are both relatively high. A rough estimate of the frequency of 63P2–61P1 transitions, compared to those from the ground level to 61P1 confirms this conclusion.

Effects of Ultraviolet Radiation

Interest in obtaining a better understanding of biological effects of ultraviolet radiation has been stimulated to a great extent dur­ ing the last few years by the wide application that ultraviolet has found as a therapeutic agent (1) in genetics (120), in the study of the fundamental structure of living cells (23), and in its wide use in aerobiology (91). This review will discuss_ the effects of ultra­ violet and visible radiation on a number of specific aspects; effects on higher plants and therapeutic applications will not be included. Recently there has become available a number of inexpensive and efficient sources of ultraviolet light. Low pressure mercury vapor lamps with glass'envelopes which emit about 80 per cent of their total and 95 per ce�t of their ultraviolet radiation at 2537 A provide a handy tool for the study of the effects of radiation. These lamps have found wide use in preventive medicine and in industrial processes. The special usefulness of these lamps lies in the fact that 2537 A is very close to the wavelength (2600 A) which is most highly absorbed by nucleic acids. Relatively low intensities of 2537 A will interfere with cell division an<;l readily inactivate many disease agents. which are not protected by other substances (53). Ultraviolet microscopy.-The striking differences in the absorp­ tion spectra of proteins and nucleic acids have been discussed in a previous review (6). The improvements in the construction and use of the ultraviolet microscope by Caspersson (23) have made possible the quantitative determination of the concentration of nucleic acids and proteins not only in the nucleus (chromosomes) but also in the cytoplasm and have made it practical to follow the change in the concentration of these compounds during cell divi­ sion (23, 24, 25). These improvements have enabled biologists to follow changes in living cells which involve as little as and often less than 10-9 mg. of certain cell constituents. Since the appearance of the classical paper by Caspers son (23) a large number of reports

The Production and Decomposition of Ozone by Low Pressure Mercury Vapor Lamps

A photo-tube method for measuring the concentration of ozone is described. Measurements were made of the rate of production and rate of decomposition of ozone in oxygen and in air by low pressure mercury vapor lamps. The production in oxygen is enhanced by the presence of nitrogen. Increasing the moisture content of the gas decreases the rate of production and increases the rate of decomposition. A new germicidal lamp enclosed in a 10-liter glass tube will form an equilibrium concentration of 145 parts per million by volume. A quartz lamp under the same conditions will form 640 parts per million. With oxygen flowing through the tube the yield for the quartz lamp is 2.5×10−3 g ozone/min. or 10 g kw hr.

Bactericidal Effects of Ultraviolet Radiation Produced by Low Pressure Mercury Vapor Lamps

The killing effect of 2537A radiation has been studied, both for bacteria suspended in air and bacteria and molds on surfaces. A 15-watt sterilizing lamp (giving 25 μw/cm of 2537A radiation at 1 meter from the lamp) will kill 97–99 percent of B. Coli suspended in air at a distance of 24 inches in 10 seconds. Accordingly in an air duct a 15-watt lamp can sterilize approximately 200 cu. ft. of air per minute. A 15-watt sterilizing lamp will kill B. Coli on the surface of agar at a distance of 10″ in 20 seconds. The Bunsen Roscoe reciprocity law applies to the killing of bacteria by ultraviolet radiation between the intensities of 2000 μw/cm2 and 1.3 μw/cm2. The lethal dose of 2537A radiation for B. Coli on agar is 6600 μw sec./cm2. For practical purposes the effect of temperature may be neglected. A film of grease is very effective in shielding bacteria from radiation. The lethal dose of 2537A radiation for black mold spores is about 45 times that for B. Coli. The reciprocity law applies. The sensitivity of mold spores decreases with increasing wave-length and is negligible for 3650A. Low pressure lamps in ultraviolet transmitting glass produce concentrations of ozone of the order of 0.1 part per million. From these experiments it may be concluded that low pressure mercury vapor lamps when used under the proper conditions are very powerful bactericidal agents if the bacteria are directly exposed to the radiation, but that the effectiveness is greatly reduced by even such slight shielding as is offered by a film of grease.

On selective absorption by luminous mercury vapour

In a previous paper published by the authors there were described, among others, experiments on the reversal of the main component of the 5461 A group of lines and its brightest satellite + 0·085 A in the spectrum of the low-pressure mercury vapour lamp. McLennan, Ainslie and Miss Cale have repeated these experiments and, in the main, confirm the results obtained by us. They, however, point out that what is taken as the main component when the green radiation is examined in instruments of resolving power of the order of 200,000 is a group of five lines of wave-lengths - 0·020 A, - 0·008 A, 0, + 0·008 A, and + 0·018 A; and they state that only the three central lines are absorbed by luminous mercury vapour, the unabsorbed satellites + 0·018 A abd - 0·020 A producing the appearance of reversal. They also describe experiments which, they consider, indicated the absence of absorption in the case of all the other components of this group, including +0·085 A. This last result is at variance with our observation of the reversal of this satellite, recorded in the paper cited above. To clear up this point we undertook a systematic investigation of the absorption of the satellites of the three lines 5461 A, 4358 A, and 4047 A (1 p 1 - 1 s , 1 p 2 - 1 s , and 1 p 3 - 1 s on Fowler's notation) the first triplet of the second subordinate series of triplets. We have observed marked absorption, under suitable conditions, in the case of all the satellites of the group 5461 A, excepting one, viz., -0·237 A, and have reversed five of them. We find that even -0·237 A shows feeble, but distinctly perceptible, absorption under exceptionally favourable conditions. In the present paper we describe the behaviour of the luminous vapour in regared to the members of this group (5461 A, 1 p 1 - 1 s ).