Improvements in Producing High Vacua.
Year: 1899

page_text: Date of Application, 22nd Nov., 1899-Accepted, 3rd Feb., 1900
Improvements in Producing High Vacua.
We, THE BRITISH THOMSON-HOUSTON COMPANY LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of our
said invention (which has been communicated to us from abroad by John W.
Howell, residing at Newark, in the County of Essex, State of New Jersey, United
States of America, Electrical Engineer), and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:
Our invention relates to the production of high vacua, and is particularly
adapted for service in connection with the exhaustion of incandescent electric
lamps. By the methods commonly employed in the manufacture of incandescent
lamps, gases, including air and hydro-carbon gases, are trapped or occluded in
the filament and its joints, and moisture is deposited on the walls of the bulb, the
last traces of which are exceedingly difficult to remove, and in the case of high
voltage lamps require for satisfactory life of the filament a long-continued exhaus-
tion by the pump. A good vacuum may be established by mechanical pumps,
the design of which is familiar to those skilled in the art, but at the expense of
considerable time for exhaustion. Methods have been designed for promoting
rapidity of exhaustion and the removal of the last traces of deleterious gases
so as to produce a satisfactory vacuum, by introducing within the bulb neutral
or inert gases, and then again continuing the exhaustion but difficulty is
experienced in providing an inert gas which is sufficiently free from impurities
to afford a satisfactory result. Other methods have been proposed for acting
chemically upon the residual gases occluded in the filament and its joints by
vaporizing solids or liquids capable of combining with them and removing the
products of the reaction.
Our process affords a means for establishing a high vacuum at a lower cost
than by any method heretofore proposed with which we are familiar.
We carry out our invention by producing a preliminary exhaustion by the aid
of a pump, for which we prefer to employ a good type of mechanical pump, and
then subjecting the lamp to external heat to drive off any moisture deposited
on the internal walls of the bulb, then continuing the exhaustion with the fila-
ment brought to incandescence. We then admit to the bulb a determinate
volume of phosphine or phosphoretted hydrogen gas at ordinary atmospheric
temperatures, which acts not only mechanically as a vehicle for assisting the
exhaustion of the residual gases by a washing out action, but establishes a
chemical reaction with such hydro-carbon vapors or air as may be present, and
thus effects their extraction from the bulb upon further action of the pump and
exhaustion of the phosphoretted hydrogen. The result on a lamp treated according
to our process is a very high vacuum and an increased output of fifty per cent., in
the product of an operator's work during a given period, and a resultant cheapening
of the cost of the lamp. This decrease in the expense is an incident principally
of the gaseous treatment by which a gang or group of lamps may be simultaneously

page_text: subjected to the action of the gas, and an attendant may therefore manage
several independent machines or exhausting devices.
No particular organization of apparatus is required to carry out our invention,
except provisions for pumping off the air or gases and for introducing the
phosphine. It will however greatly facilitate an increased output per operator to
follow the usual plan of connecting with each pump an exhaustion-tube having
a plurality of air-tight sockets or openings to receive the stems of a group of
lamps. The arrangement of such apparatus and the construction of the lamp is so
familiar to those skilled in lamp manufacture that we deem it unnecessary to
show the apparatus in detail.
The accompanying drawings shows a well-known form of lamp-bulb in which a
tubular stem 1 is left after the pillar carrying the filament has been sealed
into the neck of the lamp, and by which the exhausting processes are conducted,
after which the bulb 2 is sealed off near its junction with the stem and the lamp
is ready for the market. In practising our process the stem 1 is connected by an
elastic joint in the usual manner with a pump, for which we prefer to employ.
a mechanical pump, and a group of eight or more lamps are similarly connected
to the same pump.
A rough exhaustion is then made, and the usual tests for
defects in the lamp-structure or filament-joints made, by connecting with an
induction-coil or other source of high tension current. The filament is then
raised to a high temperature by passing a current through it, and allowed to
burn a short time to allow the pump to exhaust the occluded gases. A definite
graduated supply of phosphoretted hydrogen is then admitted to the group of
lamps by means of a controllable admission-cock connected with the exhaustion
pipe while the lamps are burning, and after a short interval, about two minutes,
the exhaustion is completed and the phosphoretted hydrogen and the products
of its reaction upon the residual gases will have been withdrawn. The phos-
phoretted hydrogen acts as a medium or vehicle to carry off the residual gases
by diffusing through-out the bulb and mixing with them, and also reacts
chemically upon such occluded gases as are capable of reacting with it.
We prefer to generate the phosphoretted hydrogen by heating phosphorous in
a solution of caustic potash, though other methods such as heating it with milk
of lime, or mixing phosphide of calcium with water, may be employed. In any
of these processes the phosphoretted hydrogen PH, is not chemically pure, but
carries with it more or less vapor of the liquid phosphide of hydrogen (P,H,)
which has a great affinity for certain gases, and especially oxygen at reduced
pressures. We believe the hydro-carbons present are decomposed by the action
of the phosphoretted hydrogen, which takes an additional atom or atoms of
hydrogen at the expense of the hydro-carbon gases in the bulb, and thereby
facilitates an almost complete exhaustion of the residual gases. The heating of
the lamp both internally and externally during the operation drives off any
film of moisture which may be deposited upon the inner wall of the globe or other
parts which is removed with the gas by the pump.
Having now particularly described and ascertained the nature of our said
invention (as communicated to us from abroad) and in what manner the same is
to be performed, we declare that what we claim is:-
-
1-The process of producing high vacua, consisting in exhausting air or other
gas from the enclosure, then admitting phospheretted hydrogen and again exhaust-
ing the enclosure.
2 The process of producing a high vacuum in an incandescent lamp, consist-
ing in first exhausting the air and other gases from the bulb, then admitting
phospheretted hydrogen, then again exhausting the bulb.
3 The process of producing a high vacuum in an incandescent lamp, consist-
ing in exhausting the air and other gases from the bulb, then admitting a com-
pound, gaseous at ordinary atmospheric temperatures and having an affinity for
the residual gases in the bulb, then exhausting the bulb,

page_text: 4 The process of producing a high vacuum in an incandescent lamp, consisting
in exhausting the air and other gases from the bulb, heating the lamp, admitting
a determinate quantity of phospheretted hydrogen, then exhausting and sealing
off the lamp.
011
1000
THE BRITISH THOMSON-HOUSTON CO. LTD.
ALFRED CLEMENTS,
Assistant Secretary,
GEORGE FRANKLIN,
W. MARTINDALE,
Directors,