An Improved Barometer.
Year: 1896

page_text: Date of Application, 31st Dec., 1896-Accepted, 31st Dec., 1897
An Improved Barometer.
I, NICOLAS GEORG GIRO, of Berlinchen i/d Neumark, in the Empire of Germany,
Engineer, 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:-
This invention relates to a barometer, in which by the use of two liquids of different
specific-weight great sensitiveness is obtained.
In the annexed drawing-
Fig. 1 shows a longitudinal section of such barometer.
Fig. 2 is a plan view and partial horizontal section and,
Figs. 3-10 are details of parts of the apparatus.
If two liquids of different density are placed in a glass tube, which is closed at the
upper and open at the under end and which has such length, that the experiment of
Torricelli, effected with these two liquids, produces the empty space of the height c
(fig. 9) whilst one of the two liquids F2 takes the position shown in the strongly
hatched lines, and the other liquid takes the position shown in faint lines, equilibrium
being obtained as represented in fig. 9; when now the air pressure increases, liquid
will pass through the open under end of the tube from the vessel to the interior of
the tube, until the pressure upon the cross section y (the geometrical position of
which we suppose to be constant) from the interior outwards becomes equal to that
from the exterior to the interior.
At a constant temperature the length h will remain the same but the length b
will increase by an amount which may be called A b, so that the vacuum space
becomes shorter by the amount (c- A b).
If the air pressure increases and the temperature remains constant, A 6 would
also depend upon the density a' of the lower liquid.
Ab represents thus the sensitiveness of the barometer.
For instance if A b is for mercury = 1 m/m, it would be for alcohol
17-15 m/m, or thereabouts.
13-596
0.793
In an experiment as above described, the liquid of the height h would always be the
Lighter one, requiring a very great tube height; to obtain a small tube height and a
great sensitiveness, one must arrange a very heavy liquid (mercury) on the top and
a very light one (alcohol) below. But this is not so easily possible, as the lower
surface of the mercury would be disturbed and the whole mercury column would
fall to the bottom.
This disturbance is prevented by a slide which gives to the lower mercury surface
a form pointed or narrowed towards the alcohol side so that even by shocks no such
disturbance would be produced as would cause the two liquids to change places-As
however at the same time also a close fit must be obtained an annular recess or
"waist" is made in the slide between the mercury and the alcohol to receive a
volume of heavy intermediary liquid which tapers off towards the alcohol side,

page_text: gold in the space between the slide and glass wall, until the weight of the slide and
the liquid in its "waist" is equal to the weight of an equal volume of mercury
displaced by the slide and liquid-The amount must be formed by weighing. Thin
gold plates form in the mercury gold-amalgam, which is denser and thicker than
mercury, and fulfils the purpose required.
In most countries of Europe the air pressure fluctuates in the usual mercury
barometer between the limits of 725 m/m and 770 m/in height. If now the liquid of the
height (fig. 9) ia mercury and h itself = 725 nun, the total average height of the
double liquid barometer =
725 m/m (45 m/m x 17, 15)
=1496-75 m/m.
To that is added the height of the case etc., so that 17m is approximately the
necessary height to be given to the instrument.
Until now we supposed only the specific weigh 8 to be variable. We now suppose,
that the air pressure itself and the densities and 8, are constant, but that the
temperature is variable. Supposing the glass tube to be divided from any zero point,
with change of temperature the glass tube will change in its length and the division
will be no longer correct. But this can be allowed for easily according to the known
laws of expansion in physics.
Supposing a division to be taken at the separating surface of the two liquids (the
under surface of the slide), the weight of the mercury above this surface would be
constant at any temperature, if the cross section of the glass tube at a change of
temperature did not change. But this is not so, for this cross section changes, and
the whole height of the mercury column therefore changes. If now the original
cross section of the glass tube Q, and the new cross section = Q(Q-Q) is the
increase of the cross section of the glass tube.
If now a means the decrease of the height of the mercury column for an increase
of temperature of to and h the original height of this column; then,

page_text: its surface an intermediary liquid (gold amalgam). The slide is shown in fig. 1- at S
and-details thereof are indicated in fig. 6. On the upper surface of the mereury
column is arranged a float, which keeps back and collects under the mercury surface
alcohol bubbles, which might eventually rise. The float is indicated in fig. 1 at P
and shown in fig. 4 on a larger scale.
On the glass tube is etched a millimeter division from a certain zero point. On
the under end of this glass tube is fixed a prolongation tube of metal (F fig. 1) which
may contain in the space F a closing cock and the under enlarged wall of which
ends in a screw. Above the closing cock this tube is so formed that it can be fixed
to the flange of the glass tube. The connection with the glass tube is however only
made, when the barometer has been filled, because between the under glass tube and
the upper prolongation tube end is arranged a conical mantle of metal, which is
shown in fig. 8 and which keeps back air bubbles which might rise.
The glass tube and the prolongation tube are then permanently connected together
and form one whole.
The barometer comprises a strongly built metal case K K K K with a tightly
closing cover Ks the interior of which is filled with a large quantity of alcohol and
upon which lie the other parts of the instrument. In the same is fixed a metal
partition G, which divides the interior of the case into two parts; this metal partition
has a screw socket, into which fits the screw of the before mentioned prolongation
tube F. It is traversed by two oylindrical borings perpendicular, to one another so
that the alcohol can flow from the interior of the case outwards only through these
borings. On the case is fixed a standard of angle iron D D, which assists in
supporting the part F and the tube EQ by means of clamps (fig. 2) which hold the
glass tube against this angle iron.
In order to determine a fixed plaue for the alcohol, the case cover is perforated at
one place and in a glass tube fixed tightly over the perforation by means of a flanged
collar is arranged an ivory point. J, over which is arranged a detachable cover.
each measuring the cover must be taken off.
The means for establishing the alcohol plane consists of two devices one for
approximate and one for exact establishment.
The approximate establishment is effected by means of a thin caoutchoue
diaphragm A B C in the form of a rectangular parallelopiped divided by a diagonal
plane and the edges of which are fixed air tightly by a rectangular metal
frame a c on the inside of the wall of the case. The caoutchoue diaphragm A B C
itself will be distended by pressure of air and drive the alcohol before it. The air
is pressed in by means of a small air pump K and passes to the side of the rubber
diaphragm remote from the rest of the chamber occupied by the alcohol. The air
pump consists of two similar parts K which are connected together by a strong
caoutchouc bulb. Each of these parts consists of a cast iron foot perforated in the
middle, on the upper part of which is arranged a caoutchouc valve as shown in fig. 5
on a larger scale over which lies a cast iron ring; these three parts are fixed
together permanently by rivetting or screwing. The caoutchouc of the valve must
be very soft, so that the pump may be very sensitive. When one presses on the
bulb, the enclosed air presses on both valves closing the upper one from the inside
outwards and opening the under one from the outside to the interior, thus eutering
the tube w which leads to the under part of the iron case, between the case and
rubber diaphragm. On releasing the bulb the inverse operation takes place, that is
to say the under valve closes and the upper one is opened. The hole in the
caoutchouc valve can be enlargod cylindrically or conically towards the base.
In order to let out the air again there is arranged at O on the 'case an orifice
closable by means of a caoutchouc plate and by a screw; by lifting the screw the
compressed air can escape. The exact establishment of the alcohol plane upon the
ivory point is effected by means of the device R; the latter consists of a strong
caoutchouc bag, which is fixed by means of a metal ring on the case wall; into the
same extends a micrometer screw with a rounded end. By screwing up the screw
the elastic bag enters the alcohol and displaces an equivalent volume of the sume.

page_text: To the instrument is fitted also a box level N for placing the instrument
horizontally. It is framed into a casing, to turn round its vertical axle. The whole
instrument rests on three foot screws, by means of which it can be adjusted to a
horizon plane.
The slide consists of a hollow body of steel or glass, as shown in fig. 6 which fits
into the glass tube in such manner, that a free space of 3-4 tenths of a millimeter
remains between it and the glass wall. The space between the exterior slide wall and
the interior glass wall R in fig. 6 is filled previously with mercury, in which as
already mentioned, some gold is dissolved. This amalgam is a very thick liquid and
possesses a great cohesion, so that, when the slide moves up and down no disjunction
of small portions of the-amalgam is to be feared,
The bottom of the slide possesses the form to be seen from fig. 6; in the same is
inserted a thin, porous, round plate (cloth, fine steel sieve, or preferably a polished
porous earth). This porous bottom to the slide has the following purpose:
It may happen that a thin alcoholic layer, especially with a quickly falling
barometer may remain still on the glass wall instead of being pressed down by the
amalgam so that the slide together with its amalgam covering slides over this layer.
When the barometer has sunk so deeply that this adhering liquid is completely
free in the mercury; it will form a bubble on receiving a shock or jolt etc., which will
rise upwards, as soon as it has obtained the necessary size. Arrived a little under
the upper surface of the mercury it will push against the under surface of the float
thereon, under which it will also remain. Therefore in time a body of alcohol will be
collected under the float and must be removed. This is effected by overturning the
whole instrument in such a manner that the case lies on the top, whilst the
overturned glass tube lies below. This quantity of alcohol rises then into the interior
of the slides and passes out again through the porous wall.
The float P consists of an ebony drum, which possesses on its side a millimeter
division from any zero-point; on the under end plane of this drum is fixed a flanged
plate hy means of a screw passing through the drum into the steel block arranged
above the drum. The flange of the plate should have a height of 3 min, but the steel
block a height of 25 mm; and the wood-drum a height of 5 mm. The steel block is
to be pointed conically at its upper end surface. When an alcohol bubble rises along
the glass wall, it pushes against the edge of the flange and enters into the space.
within the flange, on the upper surface of which (the under surface of the float) it
spreads itself out. The whole float thus rises and from the amount of this rising one
can find with sufficient approximation the height of the alcohol layer which has
passed the slide 8.
As aforesaid the drum is provided with a vertical scale of millimeter divisions and
all that is necessary is to take a note of the reading on this scale when the barometer
has been freshly overturned.
Suppose it be for instance 17 mm.; that is then to be taken as the zero-
division; if it reads after some time no longer 17 mm., but for instance 2.1 min., we
have to add to the barometrical reading at the under surface of the slide, also the
difference 2.1 - 17 min. = 0.4 mm. alcohol height of to.
With this invention, not as part of the instrument itself, but among the necessary
apparatus in the work shop, there is required an apparatus for determining the weight
of the slide 8 that is to say for counter balancing the difference in weight of a length
of tube which contains the slide and is filled up with mercury with respect to an equal
tube length filled only with mercury. In the drawing the apparatus is shown by
fig. 10. It consists of a piece of glass tube E2, 15 to 20 mm. long, the upper end of
which is set with putty in a wooden table T; the under end of the tube is polished.
This wood table T is perforated in the middle and in the upper end of the hole is set
with putty a glass tube of a diameter of 1 mm. and which tube has at a certain height
a trace as zero point (settling line). Two or three screws hold this wood table to a
second detachable wood table U lying against the finely polished end of the glass
tube. This second wood table must also be polished on its upper surface and close
tightly against the tube end when screwed up.

page_text: The equalizing of the weights is made in the following manner.
The tube E is filled up to the zero line (marked 0-0 in Fig. 10) of the small
tube with mercury and the whole apparatus is then weighed; the second wood table U
is now unscrewed after having reversed the apparatus, and the slide S is dropped into
about of its length into the glasa tube; simultaneously one lets the mercury flow
out from the underlying small tube. Then the space between the exterior slide wall
and the interior glass wall is filled with mercury and the slide is moved deeper into
the tube. Into this space is now slid some gold in thin plates, the wood table is
again screwed on and the whole is again weighed. The missing weight is replaced
by thin gold plates,
The experiment must be made as exactly as possible; therefore the whole filled
apparatus should not weigh more than 50 grammes, if one wants to bring the
difference of the two fillings exactly down to a few milligrams.
In order to fill the double liquid barometer, the glass tube E Q is at first placed
vertically, but with the point downwards. Now the float having a thread hanging
to it is slid into the still empty glass tube so that the thread comes out through the
under point. Then the finger is held against this point, whereby also the thread is
pressed against this point and the point itself is closed.
The whole tube is then filled with mereury, the thread preventing the float rising
in the mercury. Now the slide is moved carefully from the weighing apparatus
directly into the glass tube. Simultaneously one must remove the finger from over
the glass point but still always keeping hold of the thread. One moves now the slide
further into the tube, until it has arrived about 710 mm. over the outflowing point of
the mercury. Then the under end, that is the outflow of the glass point is stopped
up and the glass point itself is closed by fusing together, the float is thus freed since
the thread burns away. Now the metal piece with the device for stopping the air
bubbles is fixed on the glass tube and so much of the glass tube as is not filled with
mercury is filled with alcohol, up to the stop cock, which is then closed. But one
continues pouring in alcohol until it fills the metal tube F up to the edge; and now
a soft caoutchouc washer is put on the border of the metal piece, (the closure must
press easily against its wall) the glass tube and the metal piece are quickly reversed
(whereby the mercury comes to stand over the alcohol) and the whole is screwed upon
the part G.
Now the stop cock is opened a little by means of a metal pin. By means of
the overpressure from the interior outwards, the caoutchouc closure falls into the
beneath lying groove and frees the connection of the interior of the tube with the
interior of the case. The column of the two liquids in the glass tube falls down up
to a certain height, at which it remains standing; thus the barometer is ready
for use.
Now it is to be ascertained where the normal centre of the barometer is to be taken.
This is effected by bringing the barometer to a place, the absolute elevation over the
sea of which is known, and thus also the barometrical height. The instrument is now
observed for some time and out of the mean of its readings is ascertained the
normal barometrical state on the instrument. But this needs only to be made for one
instrument; the other instruments are then adjusted by comparison with this
first barometer; therefore it is necessary to mark the place, where the division of
the glass tube must begin. For this purpose before filling the instrument with
mercury the case with the thereover fixed glass tube is filled with alcohol and adjusted
to the ivory point and the height of the alcohol is marked on the glass tube. This state
is the zero line of the scale.
It may be mentioned, that the principle of making a sensitive baroneter by
placing mercury over glycerine creosote or water by means of a cylindrical slide has
already been used by J. Joly. But in Joly's barometer the slide does not contain
or limit any intermediary liquid (gold sinalgam) and therefore the tightening is not
sufficient. The consequence hereof is that an independent barometer is not produced
but only a comparing barometer, wherein also the vapour tension must be
considered, which arises in the vacuum in consequence of the rising glycerine

page_text: bubbles. The change of temperature is difficult to be taken into.consideration, an
the slide movement changes with the temperature (in consequence of the various
expansion coefficients) both of the slide material and of the glycerine and
mercury.
In the slide construction however, as explained hereinbefore the density becomeR
very great by interposing an intermediary liquid.and by using a float any formation
of vapour in the vacuum space is avoided. The rising variation of the slide however,
in consequence of a change of temperature is of. no importance, as the expansion
coefficient of steel and gold amalgam as well as of mercury lie very near to one
another and the slide possesses only a small steel mass. In order to prevent the
remaining of a small part of the light liquid bubble on the glass tube E, on its
passing from the glass tube wall into the interior of the space limited by the metal
flange under the float, one can advantageously cut-the glass tube E Q into two parts
at a suitable place and putty the corresponding ends into glass or metal plates in
such a manner as to obtain a tube of the length of the previous glass tube EQ by
placing these two plates over one another.
Between these two metal plates is then inserted a conical metal washer V with:a
short conical flange.
The two parts of the glass tube with this intermediary apparatus are rivetted or
screwed together permanently.
The purpose of inserting this apparatus is that the light liquid bubbles, which rise
in the glass tube wall of the under part of the tube can only escape through the open
middle of this conical mantle towards the float and (with a vertical glass tube) they
do not again come in contact with the tube wall over the mantle (that is to say in
the upper part of the tube).
The length of the two parts of the tube must be so. measured that the upper part
of the slide S comes into contact with the conical covering of the device V only at an
exceptionally high barometrical state. Such barometrical states happen. however
only very seldom and their duration is then very short.
By employing different lengths for the two parts of the tube one can when
necessary make barometers, which indicate only middle and very high, or very low,
barometrical states, but which-conversely do not operate at very low or very high
barometrical states.
When filling the barometer the float P hanging on a thread is first introduced into
the upper part of the tube and only then the two tube parts are rivetted together
with the washer lying between them. The remainder of the filling is effected as
before indicated in the description.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed I declare that what I claim
is:-
(1) A barometer with two liquids, in which the piston, which effects the separation
of the mercury from the lighter liquid contained under the same in the barometrical
tube is provided with a reduced waist which is filled with gold amalgam or the like
for the purpose of obtaining a good tightening between the piston and the tube
wall.
(2) A form of construction of the barometer as under claim (1) in which a float is
so charged by a metal cylinder, that it rises from the liquid, in which it floats, only
so far as the height of the lighter liquid which has assembled at its under plane and
is held by means of a metal flanged plate for collecting that liquid.
(3) A form of construction of the barometer as under claim 1 in which two
rubber valves arranged in hollow metal feet (each valve being formed as a hollow
rubber cylinder the wall of which is very thin from one cylinder end and increasing
very quickly in thickness, enlarges itself at its other end to a plate) are brought in
connection with a bulb in such a manner, that they form an air pump in the mannor
described.
(4) The insertion of a truncated inverted conical metal flange or washer for the

page_text: purpose set forth in the glass tube EQ by putting the corresponding ends of the
divided glass tube into metal feet fitted upon one another, such metal flange or
washer being so placed that it does not interfere with the movement of the slide S
or only unessentially so when the slide rises or falls in consequence of variations of
barometrical pressure.
HERBERT HADDAN & Co.,
Agents to Applicant, 18, Buckingham Street, Strand, London.