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586 HANDBOOK OF PROJECTION FOR
resultant pound might damage them. Examine the tube for vacuum by noting the sound the mercury makes when allowed to roll gently about in the large chamber. If it makes a clear, metallic, click, the vacuum is good, but if the sound be dull and the mercury sluggish in moving, the vacuum is either partially or wholly destroyed. If the vacuum is poor, the life of the tube may be short, or it may not start at all.
To insure careful handling and safe delivery, Mercury Arc Rectifier tubes are always shipped by express in the special box as they come from the factory.
6. Place the tube in the holder by inserting the small part of the tube just above the anode arms in the upper clip, then gently lower it until it rests firmly on the lower support. Connect the tube and beaded leads according to diagram, Fig. 191.
7. Adjustment of current (number of amperes) at the arc is obtained by connecting lead marked "X" to studs 6, 5, 4, 3, 2 or 1 of the regulating reactance. Stud 1 gives the maximum and stud 6 the minimum number of amperes.
In starting up the first time it is best to start with lead "X" on stud 6 and move toward the maximum position by steps until the desired current is obtained, as indicated by ammeter. For this adjustment it is advisable to connect an ammeter in series with the arc of the projector.
8. With the above instructions carried out, all that is necessary to start is to close switch in the 'AC" line, and bring carbons of lamp together. The automatic shaking device should then rock the tube until the tube starts. As soon as tube starts separate carbons.
9. The best and whitest light can be obtained when % in. cored carbon is used above and y2 in. solid carbon below, being careful not to get solid carbons too hard.
WESTINGHOUSE MERCURY ARC RECTIFIER.— In
Plate 1 we get a view of the front of the Westinghouse Mercury Arc Rectifier designed for use on projection circuits. It is built in 30, 40 and 50 ampere sizes, the general design, characteristics and appearance being the same for all.
Each outfit consists of a cast iron main frame on which is mounted an auto-transformer, L-L, Plate 3; reactance coil, Q, Plate 3; a tilting mechanism, B, D, K, P, Plate 2; a relay, I, Plate 3; a five-point dial switch, Plate 1, and E, F, G, H, I, Plate 2; adapting links, Plate 1; a tube and tube holder, 24,