. Journal of radiology . rm inGermany; and since tubes may befound on the American market, whichare patterned after the principles firstintroduced by Hareaus, it is importantthat a complete understanding of thistype of burner be had. 111 It consists of a quartz tube connectedat the ends to the two mercury-filledreservoirs. One of these reservoirsserves as the anode and the other as the 378 into quartz in a manner similar tothat common in exhausted glassvessels. A metallic conductorwith a coefficient of expansionnear that of quartz is found in acertain alloy of nickel and steel,but as the melti
. Journal of radiology . rm inGermany; and since tubes may befound on the American market, whichare patterned after the principles firstintroduced by Hareaus, it is importantthat a complete understanding of thistype of burner be had. 111 It consists of a quartz tube connectedat the ends to the two mercury-filledreservoirs. One of these reservoirsserves as the anode and the other as the 378 into quartz in a manner similar tothat common in exhausted glassvessels. A metallic conductorwith a coefficient of expansionnear that of quartz is found in acertain alloy of nickel and steel,but as the melting point of thisalloy is too low, and sealing it intoquartz is impossible, recourse istaken here to a ground joint be-tween a conical nickel steel plugand quartz. As one ground jointis not perfectly vacuum tight, twosuch ground joints in series areused and a seal of liquid mercuryis placed on the top of the upperground joint. On the whole, theseground joints if properly made aresatisfactory so long as they are not FICj-l. rigr. l. exposed to any considerable tem-perature rise. This limitation hasthe disadvantage of reducing thenumber of possible designs of thelamp. As compared to the arc tube, themercury reservoirs in the Heraeus typeof burner are a very large size. Thisis necessary, as can be surmised bystudy of the volt-ampere current ofquartz mercury arc lamp, shown bythe curves on Fig. 1. These curves show that when a cer-tain current is reached the voltage risesvery steeply. For the reasons of lightefficiency, the quartz lamps operate onthat part of the volt-ampere curve whichis straightest; in other words, the quartzlamp under conditions of operation is aconstant current device, so that no mat-ter what voltage is impressed, or howmuch resistance is in series, currentabove a certain maximum value cannot be forced through the tube. It isknown that the constant current valuedepends primarily on the size of themercury reservoirs by reason of the rateat which heat can be dissi
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