. Electrical world. ect of the ballast wire is to make thelesultant curve almost vertical in its working part; thus a veryconsiderable change in voltage will necessarily give rise to but asmall change in current. As constructed, the ballast is kept within remarkably small com-pass, the dimensions of a tube for a three-glower lamp, for exam-ple, being 11-16 in. in diameter and 2 3-16 in. long. The diameterof the wire varies from .001 in. in the smallest ballast to .004 the largest. The length of the wire before being given ahelical twist, is from 4 in. to 12 in. and the resistance from 25
. Electrical world. ect of the ballast wire is to make thelesultant curve almost vertical in its working part; thus a veryconsiderable change in voltage will necessarily give rise to but asmall change in current. As constructed, the ballast is kept within remarkably small com-pass, the dimensions of a tube for a three-glower lamp, for exam-ple, being 11-16 in. in diameter and 2 3-16 in. long. The diameterof the wire varies from .001 in. in the smallest ballast to .004 the largest. The length of the wire before being given ahelical twist, is from 4 in. to 12 in. and the resistance from 25 to8c ohms. The drop in the ballast is about 10 per cent, of the totaldrop between the lamp terminals. The wire is supported on a nickelstandard having a cross arm to support the wire, which is threadedthrough porcelain insulators fused on the standard with glass. Thebulb is finally exhausted and then refilled to about atmospheric pres-sure with hydrogen obtained electrolytically from an alkali solution. CDISON SiSr. FIG. 8.—OXE-GLOWER NERXST L.\MP. The heating resistances are of platinum wire coiled about porce-lain, then covered with a porcelain paste having the same coefficientof expanison as the wire, and baked. Owing to the necessity ofhaving the porcelain uniform in quality and properties, the rawmaterials are worked into the finished product at the factory—not 984 ELECTRICAL WORLD axd ENGINEER. Vol. XLIII, No. 21. only for the heating resistances but also for the mountings in thelamp frame. In the case of the smallest lamp, after baking the cov-ering cement, the rod carrying the resistance is heated to a red glowand wound on a mandrel to a spiral form, the heat being applied asthe winding proceeds. Naturally this is a delicate operation, butthe arrangement for the purpose has been so carefully worked outthat the operation is carried on by boys. .\ problem of no small magnitude was involved in realizing acut-out absolutely reliable in its action yet miniature in size,
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectelectri, bookyear1883
