IMPROVEMENTS IN APPARATUS FOR EXHAUSTING AIR FROM GLASS OR OTHER VESSELS
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by Edmund Edwards at the Office of
the Commissioners of Patents on the 25th March 1882. A communication
from abroad by Paul Clere and Alphonse Hémot, both of 18 Rue de la
Banque, Paris, in the Republic of France.
$
EDMUND EDWARDS of the firm of Edwards and Co-Patent Agents and
Engineers, of 40, Southampton Buildings, Chancery Lane, in the County of
Middlesex. IMPROVEMENTS IN APPARATUS FOR EXHAUSTING AIR FROM GLASS
OR OTHER VESSELS" [A communication from abroad by Paul Clere and Alphonse
Hémot, both of 18 Rue de la Banque, Paris, in the Republic of France.]
This invention has for its objects improvements in apparatus used for exhausting
air from globes or vessels of glass or other material by means of a column of
mercury, by which improvements a more perfect vacuum can be obtained more
quickly and cheaply, and its degree more accurately measured, than in such
apparatus as heretofore constructed and used.
By the improved apparatus hereinafter described a more perfect vacuum can be
obtained on account of the absence of two-way or three-way cocks as ordinarily
used, through which the mercury passes, and the consequent freedom from the
grease used with such cocks, which collects in the tubes retaining globules of air
and giving off appreciable vapour. The mercury operates in two capacious reservoirs
closed to the atmosphere and becoming more and more exhausted as the operation
proceeds, and in which the mercury becomes readily freed from the air which it
contains.
The extent of the vacuum formed is more accurately indicated by the use,
instead of the ordinary barometer tube in which air may remain, of the system
adopted in Macleod's sensitive manometer or gauge in which in order to measure
the degree of rarefaction of the air a known volume of the latter is compressed
against another known volume the pressure of which read on a barometer tube
indicates the pressure of the air in the apparatus with the greatest sensitiveness
and absolute exactness.
This system is directly applied in the present invention, the pressure gauge being
simplified and so arranged that it is impossible for air to pass back into the
apparatus.
The operation of exhausting the air is quicker and cheaper than is ordinarily the
case, the operation which frees the mercury from air not being performed drop by

page_text: drop but upon the entire volume of mercury which at each stroke passes into the
capacious exhausted reservoirs, whilst the mechanism consists of one apparatus
only instead of three, and can be worked by any unskilled operator.
The accompanying drawing is in illustration of the invention, figure 1 being an
elevation of the apparatus and figure 2 a section of the valve for the discharge of
the air.
A is a glass tube having a glass bulb or reservoir B at its upper part, whilst its
lower end communicates by the flexible tube D with the glass reservoir C, which
is provided at its upper end with a valve E.
A chain F works over the wheel H and is provided with a counterbalance
weight working behind the frame of the apparatus so that the reservoir C may be
made to rise and fall. The wheel H may be made to revolve in either direction
by the wheel and handle S, the wheels T, T, and the endless chain U. Or instead
of the arrangement described and shewn the reservoir C may be raised and
lowered by any other convenient means.
The tube A communicates with a barometer tube J having a bulb K at its upper
part and communicating with two or more tubes a b, one constituting what is
well known as a Geisslers tube, whilst 'the other contains caustic potash. The
barometer tube L then terminates at its lower end in an opening at M which is
connected with the glass or other vessel which is to be exhausted, a cock being
provided at N.
The reservoir B ends at its upper part with the gauge tube O graduated in equal
parts and terminating at the valve P for allowing the escape of the air. For this
valve may be substituted if desired a bent barometer tube dipping into a reservoir
of mercury or closed by other convenient device by which the escape of the air is
permitted. The reservoir C is also fitted with a valve or cock by which it can be
entirely emptied.
In figure 2 are shewn the valve m and its seat r, arranged so that the valve may
be opened or closed by the screwed spindle p operated by a handle or knob as
shewn.
The action of the apparatus is as follows:-The moveable reservoir C being
lowered, the mercury which fills the fixed reservoir B and the tube J flows into it,
the reservoir B filling with air which passes through the tubes L and J from the
glass or other vessel which is to be exhausted.
The moveable reservoir C is then raised, the mercury rising back into the
reservoir B and the tubes J and O and compressing the air before it.
When the level of the mercury has passed the point Z the air shut in the
reservoir B may be compressed into a space measured by the gradations upon the
gauge tube O which are fractions already known of the entire volume included
between the level of the point Z and the seat of the valve. The mercury continues
to rise in the pipe J, and the bulb K is intended to guard against its escape into
the tubes a, b. A moveable graduated scale, enables the difference of the level of
the mercury in the tubes J and O to be read, and this difference ascertains the
pressure of the compressed air and consequently also of the rarefied air in the
vessel which is being exhausted. For this purpose the following formula is used:-
b x d
x=
in which bis the pressure of the air in the guage tube read by the moveable scale;
d the number of divisions in the tube O; and v the known proportion of the volume
indicated by cach division of the guage tube to the total volume.
By this system the measurement of the degree of rarefaction of the air may be
effected to the millionth of a millimêtre of pressure.
When the reservoir C has been raised to the top of its stroke the valve P is
opened and the compressed air escapes through the opening m, the mercury rising
in the tube O, and the valve being reclosed upon its seat the moment globules of
mercury begin to appear in the space q, figure 2.
The operations described being repeated a certain number of times, a vacuum

page_text: may be obtained in the glass or other vessel which is to be exhausted, much more
perfect than by means of apparatus as heretofore ordinarily used.
In working the improved apparatus described and shewn certain conditions are
necessary.
For instance the vertical distance between the valve P and the bulb K should be
at least 80 centimêtres. The valve E allows communication to be made between
the reservoir C and the external air, and the entire apparatus is fixed against a
wooden frame resting upon a wooden foundation.
.
The apparatus described may be used for the purpose of exhausting glass vessels
for electric lamps or other vessels.