Improvements in Mercurial Pumps for Exhausting Gaseous Fluids.
Year: 1885

page_text: Improvements in Mercurial Pumps for Exhausting Gaseous
Fluids.
I WILLIAM FREDERICK DONKIN of Malvern Lodge, Upper Tulse Hill in the
County of Surrey Lecturer in Chemistry at St George's Hospital do hereby
declare the nature of my invention for "IMPROVEMENTS IN MERCURIAL PUMPS
FOR EXHAUSTING GASEOUS FLUIDS" to be as follows:-
My Invention relates to improvements in Mercurial pumps for exhausting
gaseous fluids, whereby their operation is expedited, and the apparatus is rendered
self-contained and compact.
In carrying out my Invention I employ a number of "fall tubes" enclosed in an
outer casing of glass or other suitable material, of a cylindrical or other convenient
section, into which the mercury is delivered, in such a manner as to enter the fall
tubes near the upper ends thereof, the upper extremity of the outer casing being
attached to the vessel from which the gas is to be exhausted. The inlets of the
mercury into the fall tubes may consist of minute orifices, so arranged as to cause
the mercury to fall in regular drops down the fall tubes. This action may be
expedited by providing that the mercury shall after passing through the minute
orifice accumulate in an interior space so as to fall in successive drops. The fall
tubes at their lower ends deliver into a second enclosing chamber from which the
gas is to be exhausted by an ordinary air pump or equivalent means, and from
which also the mercury delivered by the fall tubes is allowed to escape into any
convenient receptacle through a tube opening above the lower ends of the fall tubes
aud which may also itself act as a fall tube between the second enclosing chamber
and the final receptacle in such a way as to carry off the gas delivered by the
fall tubes.

page_text: Improvements in Mercurial Pumps for Exhausting Gaseous
Fluids.
I WILLIAM FREDERICK DONKIN of Malvern Lodge, Upper Tulse Hill in the
County of Surrey, Lecturer in Chemistry at St George's Hospital 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 improvements in Mercurial pumps for exhausting
gaseous fluids, that is to say pumps of the type of what is known as the
Sprengel pump," whereby their operation is expedited and the apparatus is
rendered self contained, more compact and less fragile than heretofore.
33
also in
In Sprengel pumps of the ordinary construction the gaseous fluids are exhausted
by the fall of mercury down narrow vertical tubes known as "fall tubes." Now my
Invention consists partly in the admission of the mercury into a fall-tube open at
both ends through a restricted lateral orifice in the same and so constructing and
arranging the fall-tube that the mercury is caused to accumulate in an interior
chamber and overflow in successive regular drops down the "fall-tube;
the employment of a casing or chamber connected both with a mercury supply and
with the vessel to be exhausted, in combination with one or more fall-tubes
enclosed for a portion of their length in such casing or chamber in such a manner
as to be surrounded by the mercury introduced into the said casing or chamber
and which is admitted into the fall tubes through a restricted lateral orifice in each
tube; further, in the combination of such a system with a second chamber into
which the tubes deliver the mercury and which is itself maintained vacuous by the
outflow from it of the same mercury through a tube acting itself as a Sprengel
pump all substantially as hereinafter fully described.
And in order that the said Invention may be perfectly understood I shall now
proceed to describe the best methods with which I am at present acquainted of
carrying the same into effect and for that purpose shall refer to the several figures
on the accompanying sheet of drawings the same letters of reference indicating
corresponding parts in all the figures.
Figure 1 of the accompanying drawings represents a vertical section of a
Mercurial pump constructed according to my Invention.
Figure 2 is a transverse section of the same.
Figures 3, 4 and 5 are sectional details illustrating three respective modifications
of "fall-tubes."
Figure 6 is a vertical section illustrating a modification of the pump and
Figure 7 is a sectional plan of the same.
A, A represent a series of "fall-tubes" of equal length (seven being shewn in the
example illustrated in Figures 1 and 2, although any required number may be
used) composed of glass or any other suitable material and either of a cylindrical
section as shewn or of any other convenient section. The upper open extremities a
of these tubes, I enclose in an outer casing or vessel B fitting over them as a cap

page_text: at b, into which casing or vessel mercury is to be admitted so as to enter the
fall-tubes simultaneously in the manner hereinafter explained. This outer casing
is connected at its upper extremity C with the vessel to be exhausted (not shewn
in the drawings) and the lower extremity is closed with a stopper or plug c
through which the fall-tubes pass airtight. Provision is made for allowing
mercury to pass into the casing B either by a lateral tube D near the bottom
thereof (as indicated in figure 1) or through an aperture in the stopper c as shewn
in Figure 6.
An important feature of the Invention is the form of the upper ends of the
fall-tubes inside the casing B. It is necessary for the most perfect action of a
Sprengel pump" that the mercury shall fall down the narrow tube in successive
and regular drops, which form a series of air tight pistons and carry down the air
or gaseous fluid between them-In the ordinary form with a single tube this is
easily effected by limiting the flow of mercury by a stop cock or other equivalent
means, the mercury then breaking into successive drops as it passes over the bend
at the top.
In order to imitate this action with a number of fall-tubes simultaneously and
uniformly, they being provided with a single supply of mercury only, this supply
may be left free and open, and the flow may be limited at the point of entry into
each tube-This may be effected in the manner shown in Figure 3. The upper
open end a of each fall-tube for a certain length from the top (which may be say
about 6 inches) is made of tube of greater internal width or diameter than the
remainder, and at or near the junction of the wide and narrow portions a short
piece of very small tube d is attached, or (if of glass) it may be drawn out from
the body of the tube in a tapering form and turned downwards, as shown in
Figure 3. The open lower end of this small tube is contracted to a very small
aperture at e. If several fall-tubes thus constructed be fitted within the casing as
hereinbefore described and set in a vertical position, and mercury be admitted into
the casing so as partially to fill it but not to rise above the open tops a of the
fall-tubes A, when the mercury rises above the small side-tubes & high enough to
overcome the capillary resistance offered by their minute orifices e, it will pass
through them into the wider internal space f and will overflow down the narrow
fall-ubes in successive regular drops as required. The particular form of tube
described may be looked on as a rudimentary "Sprengel" tube, but it is not the
only available form-Any form may be used in which mercury shall enter a
vertical tube open at the top and bottom through a lateral aperture in the same
contracted at any point so as to limit its flow the mercury then being caused to
accumulate in a wider internal chamber so as to overflow down the fall-tube in
successive detached drops-Figures 4 and 5 represent other forms adapted to the
same end. In figure 4 a minute aperture is made in the side of the tube at e;
d represents a partition across the tube inside, and fis the chamber on one side of
this partition in which the mercury accumulates before overflowing into the fall
tube In figure 5, e is the minute orifice, and d is a prolongation of the narrow
fall-tube up into the wider part above, the chamber f being thus of annular form-
This form of fall-tube is that illustrated in the general view Figure 1.
In all cases
the inner chamber is essential for the formation of regular successive drops; this
chamber may, however, be dispensed with, but in this case the mercury enters the
fall-tube in a fine jet or spray through the small orifice, and the action of the pump
is less efficient.
Although in my drawings I have represented the fall-tubes as made in one piece,
yet it is evident that the upper or wide portion and the lower or narrow portion
which in fact constitutes the fall-tube proper, may be made separately and attached
together in any suitable manner. It is also, obviously, not essential that the upper
portions a of the fall-tubes should be of increased width throughout, as they inay
be made narrow for the greater part of their length and expanded or widened at
their lower end so as to fit over the lower or narrow portion of the fall-tube,
although with the view of ensuring a free unobstructed passage for the air or

page_text: gaseous fluid, I prefer to make the upper portions a wide throughout as shewn in
my drawings.
The lower ends of the fall-tubes may deliver the mercury into an open vessel
and the ends may be turned up so as to deliver the air or gas which is carried down
by it into an inverted vessel in the well known manner-In this case, the total
length of the fall-tubes from the minute lateral orifice to the bottom must be
considerably more than the barometric height.
If it is not required to collect the air or gas delivered, but only to exhaust the
vessel or vessels attached to the casing, the action of the pump may be expedited by
using it in conjunction with an auxiliary air-pump. For this purpose, the lower
ends of the fall-tubes are left straight, and are enclosed in a second outer casing or
chamber B¹, as shewn in the lower portion of Figure 1, of a similar kind to the
upper casing or chamber B and by similar means so that the latter may be air
tight, a stopper c¹ being shown in the figure through which the fall-tubes pass-
The upper and lower casings may either partially enclose the fall-tubes as shewn in
the drawing, or they may entirely enclose the same; they may have separate
stoppers as shewn or may fit on to one and the same stopper; or they may consist
of one continuous casing or tube with an internal diaphragmn through which the
fall-tubes pass air-tight and by which they are supported. It is, however, most
convenient for the upper and lower casings and their stoppers to be separate and
distinct as in the example illustrated-The upper part of the lower chamber B¹
may be connected with the auxiliary air-pump as shewn for example at g and the
mercury which is delivered into it through the fall-tubes may be allowed to flow
out of it through a tube E, attached to its lower end, whose vertical height must be
not less than that of the barometric column, into a final receptacle open to the air,
not shewn in the drawing. If this exit-tube E is sufficiently narrow to act as a
Sprengel fall-tube, and is attached to the lower chamber in a suitable manner, and
is longer vertically than the barometric column, it will act as a secondary pump,
serving to keep the lower chamber exhausted, so that the auxiliary air pump may
be dispensed with soon after the flow of the mercury through the apparatus has
been established For this purpose, the exit-tube E may be joined to the lower
casing at the side, as shown in figure 1, or it may pass up into it through a per-
forated stopper c² (figure 6) in either case, the exit being at a higher level than the
lower ends of the fall-tubes, so that the latter may be always below the surface of
the mercury while in action-The fall-tubes may be of any desired length,
independently of the height of the barometric column; but their effective length
will depend on the maintenance of a more or less perfect vacuum in the lower
chamber.
In practice, a convenient number of fall-tubes is seven, arranged in a hexagonal
form with one in the centre and surrounded by cylindrical casings, as shown in
figure 2; in this case, the entry and exit-tube for the mercury, and the tube for
attaching the auxiliary pump, must be sealed on laterally as shown in figure 1.
If, however, one of the six outer fall-tubes is dispensed with; the holes through
the stoppers thus left open may be utilized for the tubes to admit mercury into the
upper casing and to extract air from the lower one, and the lower exit-tube may
pass up through a stopper into the lower chamber without interfering with the
ends of the remaining six fall-tubes, all as shewn in figures 6 and 7. The stoppers
may be of any material not acted on by mercury and not giving off gas or vapour
and capable of being fitted air-tight into the casings.
The tube D for the admission of the mercury into the upper casing should be of
sufficiently large section not to materially obstruct the How of the mercury-If an
auxiliary air-pump is to be used, this tube D should be connected with a reservoir
(not shewn in the drawings) containing mercury, the level of which may be kept
constant and at the barometric height below the level of the mercury in the upper
casing, or it may be adjustable so as to vary the rate of flow of the mercury, or 80
as to start the action of the pump if no auxiliary pump is used. In order to fully
utilise the auxiliary pump, a by-pass may be provided from the bottom of the

page_text: lower chamber into the exit-tube E, as shewn at h in figures 1 and 6. This
by-pass is provided with either a glass stop-cock i as shown in Figure 1, or with an
india rubber tube h¹ and clamp i as shewn in Figure 6 or any other suitable device
for effecting the opening and closure of the by-pass may be used. By opening the
by-pass at the beginning of an exhaustion the mercury which seals the ends of
the fall-tubes is run out, leaving free communication through them between the
auxiliary pump and the vessel to be exhausted, until the fall tubes are in action,
when the by-pass may be closed.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed, I would observe, that
I lay no claim to the combination in a mercurial pump for exhausting gaseous
fluids, of two or more "fall-tubes" except when they are constructed arranged and
combined together substantially in the manner hereinbefore described, but I declare
that what I claim is
1st In a mercurial pump for exhausting gaseous fluids by the fall of mercury
down narrow tubes, the admission of the mercury into a tube open at both ends
through a restricted lateral orifice in the same, the tube being so constructed and
arranged that the mercury is caused to accumulate in an interior chamber and
overflow in successive regular drops down the narrow tube, substantially as herein-
before described.
2nd The employment of a casing or chamber connected both with a mercury
supply and with the vessel to be exhausted, in combination with one or more
"fall-tubes," enclosed for a portion of their length in such casing or chamber, in
such a manner as to be surrounded by the mercury introduced into the said casing
or chamber, and which is admitted into the "fall-tubes" through a restricted lateral
orifice in each tube, substantially as hereinbefore described.
3rd The combination of a system such as set forth in the second claiming clause,
with a second chamber into which the "fall-tubes" deliver the mercury and which
is itself maintained vacuous by the outflow from it of the same mercury through a
tube connected with it acting as a "Sprengel pump,” substantially as herein before
described..