The Livgro Incandescent Lamp

Certainly one of the most interesting periods in the development of the incandescent lamp was during 1893 and 1894. Although the basic Edison patent was about to expire in the latter part of 1894, the General Electric Company was still taking apparent infringers to court, and inventors were still trying to develop lamp designs that did not infringe. One lamp that received some press coverage was made by a company that existed in Harrison, New Jersey, directly opposite the Edison Works. The lamp was designed by a physician from New York, Dr. W. E. Forest. Announcements of the lamp appeared in: Electricity, Vol VI, No 25, Jul 4, 1894, pg 315; Electrical World, Vol XXIV, No 8, Aug 25, 1894; The Electrical Engineer, Vol XVIII, N 322, Jul 4, 1894, pg 4.

The Livgro Incandescent Lamp Co. was organized with capital stock of one million dollars. The lamp could be considered a metal stopper lamp. Quoting directly from The Electrical Engineer article:

"The lamp is shown in perspective in the engraving Fig 1, and Fig 2 shows the method of construction adopted. As will be seen, the mount is a plain glass tube, A, 1 inch in length, and 1/4 inch in diameter, open at both ends. A coiled steel wire, B, 8 inches long, is placed within the tube as one of the current conductors. The bottom of the mount is set into a brass thimble, C, filled with a soft molten metal. On cooling, this metal seals the tube and fuses to the wire and thimble. The latter thus becomes the central terminal in the completed lamp.

Another coiled wire D is placed outside of the mount and passes through a pin hole in the mica disc E, projecting for a short distance beyond. The mount, with disc wires and filament attached, is then set in the neck of the lamp bulb, the whole is warmed to a proper temperature, the lamp inverted, and a soft molten metal F is poured into the bulb neck upon the disc, hermetically closing the neck.

This metal is cheap, melts at a very low temperature, and has a coeffient of expansion practically the same as that of glass. A copper conducting wire G hangs in the neck of the bulb to which the sealing metal fuses itself. This wire is attached to the screw cap for the other lamp terminal as usual.

The screw-cap, without the porcelain separator and central button, is then slipped over the bulb neck, and a fusible, elastic cement H is poured in, that fills the remaining space in the neck of the bulb, and, at the same time, fastens the screw-cap on, thus rendering plaster unnecessary. The lamp is then ready for the exhausting pump. It will be seen that this lamp has no platinum wires, no glass fusing, no plaster, no leading-in-wires, properly speaking (both conducting wires terminate within the lamp). The incandescent filament is separated from the base by eight inches of steel wire, so that heat cannot be transmitted to the seal; at the same time these wires are held by the mount so that they cannot vibrate and loosen the filament.

The inventor has devised a method of manufacturing these lamps by which hand labor will be but little used, and two or three girls can turn out several thousand per day."

The lamp was to be on the market within 30 days of Jul 4, 1894.