A Reacquaintance with the Limelight M. 9. Hocking Department of Chemistry, University of Victoria, Victoria, BC, Canada VBW 2Y2 M. L. Lambed Department of Theatre, University of Victoria, Victoria, BC, Canada VBW 2Y2 Ever wondered about the origin of the common phrase "to be in the limelight", as used to refer to a person who is in a conspicuous, favorable position before the public? T o this day, in England, the series of electric front-of-balcony lights may still be referred to as "limes" from the same origin ( I ) . The limelight of both of these expressions was a significant development in the stage lighting capability of the 19th century (Fig. 1). So called from its use of a lime or calcium oxide element heated to incandescence by an oxy-hydrogen flame, the limelight has also been known as the calcium light, the oxy-hydrogen light, and the Drummond light, after its developer. Background
To appreciate the influence of the development of the limelight on the theater scene, i t helps to visualize how this fitted into the sequence of lighting options open to theater producers of recent history. During the 17th and 18th centuries ooen candles. olaced in rows or movable chandeliers. predonlinated ( 2 , j . After 1783, when an effiricnt oil lamp was develooed. staee liehtine levels and flexihilitv were improved somewhat. begetableor whale oils were used to fuel these, since petroleum recovery had yet to be practiced. of the lass' chimneys made available-in the iast few 18th century improved both the stability and the safety of both lighting systems (4). When a method for the manufacture of illuminating (coal) gas was proven by William Murdoch in 1791, i t permitted a further flexible lighting option, a t least for the larger theaters that could afford to install their own easification plants. The improved brightness of the luminous gas flame and the greater stage lighting control possible from a single central location prompted adoption of this system by the Lvceum Theatre. London, in 1803. and hv some of the American stages by 1816 (3). But i t was not-until the mid-19th century, when the increased availability of public gas supplies made the installation of gas lighting less costly and more convenient, that this method of illumination became more widely adopted by the stage (4). Glass chimneys for gas lighting in the theater were introduced in about 1860, which again improved brightness and light stability. More importantly, this development increased the oneratine safetv of this svstem (3).In soite of these improv~ments,'direct"gaslighting was ski1 smeily and hot.. narticularlv for the .lavers . . workine in close oroximitv t o gas light* on stage, and for the balcony audience. Also the hazards irom fire or explosion from accidentnl ignition of a system leak or an unlit'fixture were high (3.51,particularly when thecomplexity ofsomeof these systemsisrealized. For example, thegas lighting systemofthe Grand Opfraof Paris used 28 milea ol'gns piping, . 88 gas . cocks, and 960 gas jets (6). It is not surprising to ikarn, therefore, that in the 19thcentury several hundred theaters are said to have burned down 'from this cause alone ( 3 , 4 ) . The limelight was first developed by Thomas Drummond for surveying purposes during the 1823-1825 period, the original tests demonstrating visibility over a distance of 66% miles (7). This was one of the first lighting systems to use a
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306
Journal of Chemical Education
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1. Photwra~h . - of about 1880, used by " . of a hand-built theater sootii~ht the Theatre Royal. Edinburgh. Top sheet-metal vent for hot gases Is clearly visible. Gas pipes originally led ima it through the sheet-metal plate on the back. Fioure
heated element, rather than the flame itself, to produce light. In fact, the very hot flame of hydrogen burning in oxygen is itself invisible. But when directed onto a spot on the surface of a piece of calcium oxide, the oxide was heated to incandescence, demonstrating the first incandescent lieht. I t is ioterestine to sneculate whether the develooment orthe modern electric l i g k bulb would have taken the same course, without these early incandescence lighting developments. Incandescent lime oroduced a lieht - that was intense and powerful, easily competitive in these respects to an elertrir arr. an alternative available durinr the 1850-1880 ppriod ( I . 3). ~ uthe t arc lamp was noisy, itsintensity was n i t significantly adjustable as the limelight was, and it produced a harsh light (6) unlike the inherent softness of the limelight. Early adoption of arc lighting also suffered from a lack of available public electric power supplies, which only became accessible by about 1880 (8). For these reasons the limelight was in significant use by the stage, as well as in lighthouses, by 1855 (2,3,6). Hydrogen gas was prepared, in the early days of the limelight, by adding dilute sulfuric acid to granulated zinc (9). Oxygen was obtained by heating manganese dioxide, or less expensively by heating a mixture of manganese dioxide and Author responsible for the actual assembly and demonstration of the version of the limelight described here. Present address: 324-8 Somerset Street West. Ottawa. ON, Canada K2P OJ9.
potassium chlorate, or sodium nitrate alone. Both gases were bubbled through water to clean them, and then stored in large, hellows-shaped bags of rubberized fabric or leather. Equal weights were applied to the bags to obtain the equivalent pressures required from the two gas streams. Even -~ thoueh the cvlindrical lime element of the limelieht required periodic adjustment for optimum performance, i t nrovided a sufficientlv oowerful and concentrated light source that i t was o n e or the first that could be used f o r remote lighting of the stage, from behind the proscenium arch. I t could also be focussed and was fitted with a lens and enclosure both for general floodlighting and for use as a spotlight. Also the brightness flexibility lent itself to special effects such as sunlight, moonlight, lamplight, cloud effects, and water ripples (6). These factors all contributed to the widespread adoption of the limelight in the theater by 1860. Gas was still used for heating the gas mantle (the Welsbach mantle) lighting system, introduced in the late 1880's (3. 10). Here too. lieht was indirect. as with the - nroduction . 1ime1i'~ht.A nonluminous gas flame from a ~ k s e burner n was used to heat a delicate network of thorium and cerium oxides that became incandescent and provided the light (11). This develooment drew from the incandescent lighting . . experience of the limelight, and it paralleled the improvements of the limelight and electric filament lamps in both brightness and the amount of light possible per figure (1,3). But, because of its lateness, i t failed to compete effectively with the more convenient electric lighting developments of the same period, and therefore was never widely adopted by the theater. It is a system that still survives, however, for portable lighting remote from electric power supplies. The cotton from a cvlindrical cotton baa saturated with the appropriate salts is flared away, leaving the oxide network incandesce brightlv in the white gas, . kerosene, or propane . . flame used to (eatlt. Electric incandescent lighting was developed in the 18601880 period when the limelight was already well established (2,6). The combined efforts of Joseph Swan in England and Thomas Edison in the U.S.A. provided this more convenient, safer lighting option to the theater. Like the limelight this svstem nroduced lieht indirectlv. from a hot element. but tgis time the heat source was el&ricity instead of gas. The Grand OnBra in Paris. and the SavovTheatre inLondon installed e l e r k v lighting in 1880 and 1881, respectively (ti). But it wai the demonstration of electric lirhting in a Munich theater, installed for an exposition of 1882, t h i t really provided the stimulus for its widespread adoption (3, 6). By 1890 electrical lighting systems had been installed in most theaters, and by 1900 electric incandescent lamps were in almost universal use (1, 6). The electrical conversion effi~
Table 1.
~~
Carbon Dloxlde Dlsloclatlon Pressures of Calcium Carbonatea Temperature
Pressure
I0O
imm Hd
ciency of these early bulbs was less than a 10th the efficiency of modern bulbs. about 1.5 versus the present-day average of 20 lumens per a a t t (6). everth he leis, they w&e so much more energy efficient than any form of gas lighting that now, for the first time, theaters had to install heating plants to keep patrons warm (3)! Today all types, colors, and intensities of electric lighting are used, from a variety of spotlights to floodlights and special effects lighting, safely and efficiently to achieve every conceivable type of lighting effect. The Demondratlon
While the period limelights usually employed a hydrogenoxygen flame, coal gas-oxygen mixtures were also used (5, 12). Present-day burner comhinations and fittings were not readily available for these gas comhinations, but oxy-acetylene eouinment and eases were available and a o ~ e a r e dto be capabie df meeting &e requirments. A simpleckfirmatory test was conducted, usine a standard oxv-acetvlene welder's of manually torch to heat an upper corner of a 4-cm comnacted. ~owderedcalcium oxide resting on a nonflammable surface. The powerful incandescence was clearly demonstrated hut was not amenable to operation for more than a few seconds to a minute at a time. 1t&o could not be readily adapted for a stage lighting demonstration. T o satisfy these requirements meant assembling a rigid lime element plus adjustable mounting and heating system into an enclosure fitted with a lens for focussing. Lime Elements
The hard, cylindrical lime elements, once available commercially a t low cost, had first to be made from scratch. Calcium oxide powder, when tightly rammed into a cardboard tube, could neither he removed from the tube nor cut free of the tube without crumbling. Use of any common type of adhesive would introduce a combustible component to the lime.. .vet adeouate lime cvlinder strength was necessarv to enableclamp& and adjuitment. ~ o w & e r high-grade , limestone cCaCO.1 cores were available from a local rement company, from which i t was thought possible that high-density limes could be prepared. A test was needed to determine if, with slow heating and subsequent cooling, cores could he calcined to calcium oxide (eq 1) without disintegrating to a powder. CaO + CO,
CaCO,
(1)
Consideration of the temperature-carbon dioxide dissociation pressure profile for calcium carbonate (Table 1) prompted the first heating schedule tested. For core samples of 201.77 g and 178.32 g, the temperature was raised and lowered in the following steps: to 450 OC, 4 h; to 860 "C, 2 h; to 950 O C , 2 h; a t 950 "C, 20 h; to 1000 OC, 1h; a t 1000 "C, 4 h; to 30 "C, 12 h. The initially gray cores had substantially retained their orieinal cvlindrical shapes. with onlv. slieht distortion, and hetame pure white. More importantly, they still maintained sufficient strenath - to he useful as incandes. cent elements in a limelight. An additional back-up and replacement series of limes was prepared (Table 2). This was necessary because, when lime is exposed to the atmosphere a t ordinary temperatures, it gradually reacts with both carbon dioxide and moisture (eqs 2-41, CaO
+ H,O
CaO + CO, Ca(OH), + CO,
-
Ca(OH),
(2)
CaCO,
(3)
CaCO,
+ H20
(4)
While these processes form a useful part of the setting reaction in plasters and in lime mortars (11), if they occur to any significant extent to a limelight element, they make the material useless because it fractures immediately upon strong heating. Volume 64
Number 4
April 1987
307
Llmellnht - Assemblv
ment and the acetylene burner constant for focussing adjustments. Valves for the separate oxygen and acetylene supply external to the lamp housing were part of the standard torch butt, so that this completed the gas-handling and burner requirements of the limelight.
Component assembly concentrated on producing a functional limelight rather than a historically accurate model, although from early catalog illustrations (Fig. 2) this functional version included all important operating components of the originals. A 1930's electric plano-convex spotlight was modified for the lamp housing. The electrical fittings on the original focussing support frame were replaced with a threaded lime adjustment spindle topped by a sheet metal lime clamp (Fig. 3). Standard oxy-acetylene welding equipment was adapted for fittine into the honsine in such a wav as to direct the flame a t ;he lens side of thelime elernent.;~t the same time it was mounted in such a wav that it ~ e r m i t t e dadiustment of the gas flow rate by valve locations outside the housing. The whole hurner assembly was bolted to a movable focussing frame to keep the spacing between the cylindrical lime ele-
Demonstration All the gas handling precautions of standard acetylene welding manuals were followed, e.g., references 15 and 16. One- and two-stage regulators were connected via cleaned fittings to the acetylene and oxygen cylinders, respectively, to s t e down ~ cvlinder Dressures to the lower workine- DIeS. sures required. Five pounds per square inch for both gases was convenient. Whatever Dressure is selected. however. it is important that i t he the same for oxygen and &etylene,'as a safety precaution. With the operator wearing a face shield or weldinggoggles, Full details can
F gurr 2 Pnofuqrapnof the work ng camponenls of a mwsa jet i me ight hom m e coilect~onof MLL (above! and a reproduction of an 1891-1892 catalog 1l.rtral on of the same type of gM (Below). The cylindrical ifme elcmem plls remote means of rotating and raising or lowering relative to the burner on the right are clearly visible. Valves for gas control are visible on the top left and. lower down, a cut-off laver that allowed me operator to turn down the flame to "pilot light.' size without altering me main valves.
be provided by either author, on request.
Figure 3. Cut-away diagram of our limelight fining to an electric spotlight. LBtemI movement of the lighting within the enclosure, far focussing, is controlled by the knob an the ien. Llme rotation and adjustment Is by the bonam knob. immediately to the right of this control is Me torch bun assembly wim flexible torch fining and burner aimed at the lime cylinder. Lens for focussing the beam by lateral movement of Me lime assembly is on right side of box.
Table 2. Dlmenslonal and WelgM Losses ot Dense Limestone Cores on Heatlnga Cwe NO. 1. 2 3
Dimensions i X diam (mm) Initial Final
Mass
Initial (g)
% Loss 42.43 41.19 41.90 41.62
4
104 X 27 96 X 27 110x27 93 X 27
102 X 97 X 109 X 91 X
25 25 25b 25
156.91 145.31 166.22 143.19
5 6 7 8
107 X 27 113 X 27 115x27 90 X 27
105 X 103 X 106 X 66 X
24 23 24 23=
160.43 171.60 160.27 140.13
.
42.83 42.96 42.50 43.14
% Loss
Gmup Means % of Theory
41.79'
95.03
42.66.
97.47
C m e nllmbers 1to 4 were heatedaccordinglomefoliovlng8 M u i e : t o 200% 1 h:to 620 'C. 4 h: at 8 2 0 % 14 h:to 1030 "C. 3.5 h:to-200 'C. 0.5 h: finai cooling in desiccator. Care numbers 5 to 8 had the s a w heating acheauie, omming the la* cwilng steps, as o m numbers 1 to 4, plus a further 1000 'C. 14 h; to -200 OC, 5 h; finai cwiillg in deolccator. *Had a 12 m m ion9 axiai crack st one end. CDevelopedan 8' lsnglhwi~eband.
308
Journal of Chemical Education
a very gentle flow of acetylene to the torch tip in the lamp was lit with a spark lighter. This gave a small, highly luminous yellow flame. The flow of acetylene was then adjusted using the torch hutt control until the flame tended to jump just slightly away from the torch tip. The butt valve for oxygen was then opened slightly, and the flow gradually increased until the luminous flame became pale blue. When the inner blue, cone-shaped center of the flame was softly rounded a t its tip and came just short of the lime cylinder, optimum burner operation and light output was obtained. The beam produced was powerful but soft in quality, not harsh. With slightly less oxygen than this, the inner blue cone of the flame hecame larger and feathery in outline, and some lamp brightness was lost. With too much oxygen, the blue cone became very sharp at the tip and was often accompanied by a hissing sound. Dark welding goggles were required to observe all of these operating adjustments because of the high intensity of the limelight. The side of the lamp itself could, with advantage, be fitted with a dark green window to be used for this purpose. Once the burner had been properly adjusted, the size of the lighted spot and the lighting distance wanted could be easily controlled by sliding the whole lime plus burner assembly toward or away from the plano-convex lens. A slot running the length of the lamp base plate allowed free movement of lime adjustment spindle and the torch flex fitting for focussing purposes. Gradually, during 2 to 8 minutes operation, a small crater developed on the surface of the lime cylinder. Slowly turning the lime adjustment spindle a few degrees exposed a fresh lime surface to the oxyacetylene flame, which maintained the quality and intensity of the light without interruption. If a longer interval was allowed between lime adjustments, the light quality and intensity deteriorated, and the focussing changed as a deeper crater developed in the lime. Again this could he corrected hy simply rotating the lime adjustment spindle a few degrees. Eventually, however, after an hour's operation or so a groove of near-connecting craters was worn all the way around the lime cylinder. The lime adjustment spindle then had to he turned quickly two or three times to raise the cylinder slightly and expose a fresh ring of lime surface to the flame. A coarser thread on the lime adjustment spindle would avoid the need for this gross adjustment step. I t should be pointed out that the observed cratering is an integral part of the light generation process of the limelight and not merely an operating nuisance. Calcium oxide, whether heated by oxygen combustion of coal gas, hydrogen, or acetylene fuels, gives off additional radiation as a result of chemical interactions at the surface. This is the so-called "enhanced radiation", which is produced in addition to the predicted levels of thermal radiation from the hot surface because of the excitation of the constituent atoms during these chemical reactions (12). To shut down the lamp it was found advisable to turn off
the acetylene valve first, then the oxygen. to avoid the soot deposits produced hy a straight acetylene flame. The lamp was allowed to cool fullv t~eforeartemntinr to relieht in order to avoid the risk "of an explosioA wzhin the-lamp housing if the flammable gas mixture should contact a hot lime element. Finally, once the cylinder main valves were shut off, any residual pressure in the regulators and connecting hoses was bled from the system, one gas a t a time, through the torch hutt valves, when the lamp was cold. An air-tight container is necessary for proper storage of prepared limes, because of the reactivity of calcium oxide with both carhon dioxide and moisture. A polyethylene bag is only adequate for short-term storage. Over a storage period of4.5 in 2-mil polyethylene; substantial deterioration of the dense, cylindrical lime elements took place, giving a loose powder accompanied by a 28 to 33%-increase in weight (Table 3). Formation of calcium carbonate from lime would require a 78.5%weight gain. Formation of calcium hydroxide reiuires a percentage weight rain of 32.1. quite close to the observed increases. ~olye&yleneis also 3 4 times more permeahle to water vapor than to carbon dioxide3 (17),and the mean concentrationof water vapor in air here is also some40 times higher. Therefore, from gravimetric and permeability considerations it seems likely that this initial powder was calcium hydroxide (slaked lime). Once the nowder was removed from the nrotective nolv" ethylene film, a slower reaction with carhon dioxide caused a continued increase in weight. Indications are that this reaction had not gone t o completion in the time frame allowed (Table 3). although treatment with dilute hydrochloric acid confirmed the presence of carhonate. Nineteenth century lime elements were also highly susceptible to carhon dioxide and moisture uptake. When left exposed to the air for more than a few hours they were rendered useless (9). The spoiling process was slowed by wrapping in dense paper, or by dipping the element in wax, which would r a.~ i d.l burn v off in use. Loneer term storaee " was obtained by keeping prepared lime elements in a sealed can. Substitute elements such as fireclay or firebrick, which would avoid this atmospheric instability problem, were confirmed to he useless for light production. Magnesium oxide, which had greater atmospheric stability, had been found to produce a light of less than half the brightness of calcium oxide (9).Certainly limestone (CaC03) itself could not he used, as confirmed experimentally by ourselves, since it rapidly fractured and crumbled away a t heating. Equivalent brightness was obtained momentarily, hut only until pieces of the partially decomposed limestone fell off the heated spot on the limestone cylinder. The rate of cratering oh~
&
Permeability Constants for lowdensity polyethylene (0.922 g/mL) are GO,, 280; H20. 800; and for highdensity polyethylene (0.954 glmL) are CO2. 43; H20. 180 (17).
Table 3. WelgM Gain of Calclum Oxlde Bagged In 2-mll, Low-Densky Polyethylene and Open to Alr for Varlous Tlmes Weight Gain
Recwded
Treatment Details
WebM (g)
g
%
56.76 65.79
33.03 38.29
Limes 3 d 4 * : initial,as CaO 54 months in polyelhylene 54 months in polyeth. 1 mo. in air 54 months in polyeth. 6 mo. in air 54 months in polyeth. 7 mo. In air 54 months in polyeth. 8 ma. in air 54 months in polyeth. 12 m. in air
+ + + + +
Limes 7and8: initial, as CaO
171.84
62 months in polyethylene 62 months in polyeth. 4 mo. in air
228.60 237.63
+
Volume 64
Number 4
A[ ril 1987
309
provomtive opinion "Congratulations, You Have Just Destroyed Yourself" Or "How To Fail in Chemistry without Really Trying" Kenneth Ndon Carter and Eugenia G. Carter Presbyterian College. Cllnton, SC 29325
The evolving of the study guide into the current volume, which is often as large as the encyclopedic text itself and which proudly proclaims that all of the text's many problems are worked out in complete detail, has resulted in the loss of an important dimension in chemistry teaching. In a perfect world with perfect students, this availability of instant, easy solutions would be immaterial, hut even the newspapers do not print the solution to the crossword puzzle until the next day. Theabove is from the abstract of our presentationmade at a recent ACS National Meeting. The iesponse by teachers was favorable. More detailed discussion with the author of a much-used general chemistry text resulted in the promise that the next edition would contain some problems without anv answers eiven. However. discussion with the reoresentative of a company that pubiished an excellent n e k organic text ended in a rather abrupt dismissal with the comment that since they consider college sophomores completely mature, the problem does not exist. I t has been only a few years since one saw statements about the adverse effects of using fraternitv files; a t that time, some textbooks contained a large number of problems (frequently with answers for half) so that at least some fresh onescouldbe assigned for homework each year for the entire
910
Journal of Chemical Education
period of use of the text, with new problems a s one of the major selling points of the new edition. We have "come a long way, baby," to the present point where i t seems that the only possible additional item in the "complete package" accompanying some texts would be the inclusion of a live urofessoi (if. indeed. with so manv "helns". one is needed a t all). M'r realize tha; waching mAhods'va&, hut that is no reason for all oroblems to be orovided with readilv available solutions. he most recent nkw text we have received came with a brochure stating that, if the text were adopted, each student would receive free manual with step-hy:step solutions to all problems in the text. Our examination would have been more thorough had the manual contained only half of the solutions. This naoer is not a condemnation of teachers whose metbods reqkre large numbers of solved problems; i t is a plea for aid for those (and thev are manv) who feel as we do. Life does not provide dasi~yobtained complete solutions to all problems; neither should textbooks.
a
Presented in part at the 188th National Meeting of the American Chemical Society, Philadelphia, PA, Aug. 1984: Abstract CHED 57.
