Improvements in the Production of Vacuum, and Means for that Purpose.
Year: 1893

page_text: Date of Application, 9th Jan., 1893
Complete Specification Left, 9th Oct., 1893-Accepted, 11th Nov., 1893
PROVISIONAL SPECIFICATION.
Improvements in the Production of Vacuum, and Means for that
Purpose.
I, JAMES DEWAR, of No. 1 Scroop Terrace, Cambridge, in the County of
Cambridge, Professor of Chemistry, do hereby declare the nature of this invention
to be as follows:-
My invention has more particularly for its object to attain a high degree of
vacuum in closed vessels by simple and expeditious means, not involving the use of
a mercurial air pump, which has heretofore been the most effectual means employed
for this object.
For this purpose, I fill the vessel to be exhausted with a condensible vapour in
such manner as to entirely exclude the atmospheric air. I then subject a portion
of the vessel which can be hermetically sealed off from the main body, to a lower
degree of temperature than the main vessel, by which means the vapour contained
in the main vessel will descend into the subsidiary vessel and become condensed
therein, thus producing a more highly vacuous space in the main vessel, the lower
the temperature is to which the subsidiary vessel has been subjected.
Having thus obtained the degree of vacuum required, I then separate the
subsidiary vessel by hermetically sealing it off.
The vapours which may be used with advantage for this purpose are very
numerous, but I prefer to use substances of high molecular weight in the form of
vapour, being either elementary or compound bodies, such as, in the case of
elementary bodies, mercury, iodine, sulphur or selenium, and, in the case of com-
pound bodies, volatile inorganic or organic substances. In carrying out the said
process I prefer to proceed as follows:
For example, if the vessel to be exhausted be of glass, such as the globe of an
electric incandescent lamp, I connect therewith by a small tubular passage a small
subsidiary vessel or separate little enlargement of the main bulb. I introduce into
the bulb a small quantity of mercury or other substance such as before mentioned,
and I then connect the bulb with an ordinary air pump, the exhausting action of
which is maintained. By this means the pressure of the air in the bulb is reduced
to, say, inch pressure of mercury, or less, according to the efficiency of the
pump. The vessel is now inserted into a chamber which can be heated to such a
temperature as to rapidly distill the mercury, the vapours of which are received
and condensed in a separate vessel beyond the hot chamber. After a short time
the mercury vapour will have displaced the whole of the air from the main and
subsidiary bulbs.
While the air pump is still working I now seal off the combined bulbs from the
air pump and condensing vessel, at the same time cooling the heating chamber,
whereby such sealing is easily accomplished. I then remove the combined bulbs
from the heating chamber, when, on cooling, a portion of the vapour of mercury
which filled them condenses in a liquid form; this is transferred to the subsidiary
bulb, and any particles adhering to the glass of the main bulb is removed by
heating this so as to volatilise the mercury and cause the vapour to condense in
the subsidiary bulb, which is kept at a lower temperature.
On now sealing off the subsidiary bulb, the main bulb is left in a highly
exhausted condition, the degree of perfection of the vacuum depending solely
upon the reduction of temperature to which the subsidiary bulb is subjected,
•
'

page_text: provided the boiling out has been so conducted as to leave substantially nothing in
the bulb but the vapour of mercury.
Dated this oth
1000
ABEL & IMRAY,
Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in the Production of Vacuum, and Means for that
Purpose.
I, JAMES DEWAR, of No. 1 Scroop Terrace, Cambridge, in the County of
Cambridge, Professor of Chemistry, do hereby declare the nature of this inven-
tion and in what manner the same is to be performed to be particularly described
and ascertained in and by the following statement :-
+
My invention has more particularly for its object to attain a high degree of
vacuum in closed vessels by simple and expeditious means, not involving the use of
a mercurial air pump, which has heretofore been the most effectual means employed
for this object.
For this purpose, I fill the vessel to be exhausted with a condensible vapour in
such manner as to entirely exclude the atmospheric air. I then subject a portion
of the vessel which can be hermetically sealed off from the main body, to a lower
degree of temperature than the main vessel, so that vapour passes from the main
vessel into the subsidiary vessel and becomes condensed to a liquid or solid form
therein, thus producing in the main vessel a vacuum the higher the lower the
temperature to which the subsidiary vessel is subjected.
Having thus obtained the degree of vacuum required, I hermetically seal off the
subsidiary vessel.
The vapours, which may be used with advantage for the above purpose are very
numerous, but I prefer to use substances which have high molecular weight
when in the form of vapour, these being elementary bodies, such as mercury,
iodine, sulphur or selenium, or compound bodies such as volatile inorganic or
organic substances, by preference such as boil at high temperatures without under-
going chemical decomposition producing more volatile dissociated products.
In carrying out the said process I prefer to proceed as follows.
If for example, the vessel to be exhausted be of glass, such as the globe of an
electric incandescent lamp, I connect therewith by a small tubular passage a sub-
sidiary vessel or separate small enlargement. I introduce into the bulb a small
quantity of mercury or other substance such as before mentioned, and I may then
connect the bulb with an ordinary air pump by which the pressure of the air in
the bulb is very much reduced.
While the action of the pump is maintained the bulb is heated, preferably by
introducing it into a chamber which can be heated to such a temperature as to
rapidly vaporise the mercury, the vapours of which are received and condensed in
the subsidiary vessel outside the hot chamber.
The mercury vapour in a short time displaces the whole of the air from the main
and subsidiary bulbs.
While the air pump is still working, I seal it off from the subsidiary vessel and
bulb and I then cool the heating chamber or remove the bulb from it.
When the bulb is cold, a portion of the vapour of mercury condenses in a
liquid form; this is transferred to the subsidiary bulb along with any mercury that
had not been vaporised, and any particles adhering to the glass of the main bulb
may be removed by heating this so as to volatilise the mercury and cause the
vapour to condense in the subsidiary bulb, which is kept at a lower temperature
and in such a position that the mercury cannot flow back from it into the bulb.
.
On now sealing off the subsidiary bulb the main bulb is left in a highly exhausted.

page_text: condition, provided the boiling out has been so conducted as to leave substantially
nothing in the bulb but vapour of mercury.
Although I have mentioned mercury as the substance employed in the process
above described, other substances, such as I have above referred to may be employed,
but I prefer mercury as being most convenient and accessible.
Bulbs for incandescent electric lamps with the filaments in place may be
exhausted in the manner described, and the heat for the purpose may be partly
obtained by passing an electric current through the filament, this also serving to
remove the occluded gases.
When the vessel to be rendered vacuous is of material other than glass, as for
instance iron or steel, the process is carried on in the manner described, the sealing
off requiring a higher temperature, which may be obtained by using an
oxy-hydrogen blow pipe.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
The herein described process for production of vacuun: by vaporising mercury
or other suitable substance in a main vessel or bulb having a subsidiary vessel
communicating with it through which the vapour passes sealing the outlet from
both vessels, condensing vapour and collecting the condensed material in the
subsidiary vessel, and then sealing it off from the main vessel or bulb.
Deted this 0th dow of Datahom 1002
ABEL & IMRAY,
Agents for the Applicant.