Improved Manufacture of Electrical Vacuum Tubes.
Year: 1897

page_text: PROVISIONAL SPECIFICATION.
Improved Manufacture of Electrical Vacuum Tubes.
I, FREDERICK HARRISON GLEW, of 156, Clapham Road, London, S.W., Chemist
& Radiographer, do hereby declare the nature of this invention to be as follows:-
My invention relates to the introduction of various substances into vacuum tubes,
which substances are capable of being decomposed by heat, sufficiently to give off
gas to the desired degree to yield any required pressure for any particular effect
of electrical discharge, especially for the production of Rontgen rays.
Electrical vacuum tubes as at present constructed, especially those for use in
generating Rontgen rays, soon loose their efficiency in use, in consequence of a
variation of the pressure of the residual gas, for in use the vacuum is constantly
getting higher until at last the tube refuses to act properly.
My invention provides a means of liberating a fresh supply of gas, or gases, into
I find a con-
the tube, so that the internal pressure can be controlled to any extent.
venient way of putting my invention into practice is as follows
I enclose within the exhausted tube some substance capable of giving off gaseous
products when decomposed by heating, such as resins, shellac, gums, sugars, sealing
wax & other organic substances, or in some cases certain suitable inorganic
substances for instance chlorate of potash, nitrate of potash, or nitrate of ammonia
or other suitable salts, either in fragments or preferrably as coating adhering to any
convenient inert body.
I prefer to spread, the substances which are to be decomposed by heat, on wires
by painting or dipping the wires into the fused substance or substances or by
dipping or painting thereon solutions of the substances which are to be decomposed.
I prefer to use thin soft iron wire for this purpose.
Having coated the wire with the substance to be used, I then cut the wire into
short convenient lengths & insert one or more of these into the tube which is then
pumped in the ordinary manner & sealed off in the regular way-now when it is
desired to increase the pressure of gas in the tube, one or more pieces of the coaited
wire is selected & brought into a convenient part of the tube by acting upon the
iron wire by means of a magnet, held outside the tube, and when in position, that
part of the tube is gently heated by a flame until decomposition begins and which
can be thus regulated by heating until the desired internal pressure of gas is
obtained. Of course the substance to be acted upon by heat may be simply shaken
into position, but in practice it is more convenient to be able to well select &
arrange in position by the aid of a magnet or magnets.
AT 1th 1007

page_text: FREDERICK HARRISON GLEW, 156, Clapham Road, London, Chemist and Radio-
grapher, do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement:-
My invention relates to the introduction of various organic or inorganic sub-
stances into vacuum tubes, which substances are capable of being permanently
decomposed by heat, to give off gas, sufficiently to obtain any required pressure, to
obtain any particular electrical effect, particularily the production of Rontgen's
rays.
Electrical vacuum, tubes as at present constructed, especially those used for
generating Rontgen rays, soon loose their efficiency in use in consequence of a
variation of the pressure or amount of the available residual gas, for in use, the
vacuum gets constantly higher, until at last the tube refuses to act properly.
My invention provides a means of liberating a fresh supply of gas, or gases,
within the tube, so that the internal pressure of gas can be controlled to any desired
extent, and remain permanently so.
I find a convenient arrangement is to enclose within the exhausted vacuum tube,
some substance capable of liberating permanent gaseous products, when decomposed
by heat, such as resin, shellac, sealing wax, gums, sugar, or other organic sub-
stances capable of permanent decomposition-and in some cases I use inorganic
substances, such as, chlorate of potash, nitrate of ammonia, or other suitable sub-
stances, capable of evolving any gas or vapour, when decomposed by heat, which
gas will thereafter remain permanently disengaged.
I am aware that caustic potash, (hydrated) and some other substances have long
been used for the purpose of regulating vacuum tubes, but these are not suitable for
very high vacua, in practice, because the gaseous products of decomposition are
reabsorbed again when the heat is removed, so the result is not a permanent
liberation of gas.
I place these above mentioned resinous or other active substances within the tube
before it is exhausted, either in the form of small fragments, about one hundreth
of a grain each, more or less, or preferably as a coating on wires.
I prefer to use the decomposable matter in the form of a coating on iron wire,
in this case I take soft iron wire, about No. 28 guage, in pieces about half an inch
long, I then coat these with the decomposable matter, previously made fluid by heat,
or by any suitable solvent, the wire is then covered, wholly or partly, by dipping,
or by painting the substances thereon, so that about one hundredth of a grain,
more or less, of the active substance is left adhering to the wire.
When cold and dry, one or more pieces of the coated wires are placed within the
tube, which is to be exhausted by pumping in the ordinary way, the tube is then
closed by sealing off in the ordinary way, when the desired vacuum has been
obtained by pumping.
When it is desired to increase the pressure of the gas within the tube, one of the
pieces of active matter or a piece of the coated wires, is selected and brought into
any convenient part of the tube, by shaking, or by means of a magnet used outside
the tube, this piece of active substance having been drawn away from the rest,
can be acted upon locally by a source of heat applied outside the vacuum tube,
hear that part, without heating the other pieces of active substance. In use, the
heat is gently applied until the decomposition of the resinous or other active
substance begins, and the heating is continued until the necessary amount of

page_text: evolved gas is obtained, which is at once evident if the vacuum tube is connected to
an induction coil during the process, these operations can be repeated from time to
time as required.
I may place the active substances either in the main chamber of the vacuum
tube, or in any convenient side tube communicating with the main chamber.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:-
1st. The use, in electrical vacuum tubes, of shellac, resin, sealing wax, and
similar resinous, or other organic substances capable of being permanently decom-
posed by heat, substantially as described.
The use in electrical vacuum tubes, of chlorate of potash, nitrate of ammonia,
or other inorganic substances, capable of being permanently decomposed by heat,
substantially as described.
Dated this Fourth day of August, One thousand eight hundred and ninety
FREDERICK HARRISON GLEW.