Pump Primer 1 $100 - 8 Hours - Technical Learning College

Burgomeister of Magdeburg
The remarkable Otto von Guericke (1602-1686), Burgomeister of Magdeburg, Saxony, took up
the cause, making the first vacuum pump, which he used in
vivid demonstrations of the pressure of the atmosphere to the
Imperial Diet at Regensburg in 1654. Famously, he evacuated
a sphere consisting of two well-fitting hemispheres about a foot
in diameter, and showed that 16 horses, 8 on each side, could
not pull them apart. An original vacuum pump and hemispheres
from 1663 are shown at the right (photo edited from the
Deutsches Museum; see on right). He also showed that air had
weight, and how much force it did require to separate
evacuated hemispheres. Then, in England, Robert Hooke
(1635-1703) made a vacuum pump for Robert Boyle (1627-
1691). Christian Huygens (1629-1695) became interested in a
visit to London in 1661 and had a vacuum pump built for him.
By this time, Torricelli's doctrine had triumphed over the Church's support for horror vacui. This
was one of the first victories for rational physics over the illusions of experience, and is well
worth consideration.
Pascal demonstrated that the siphon worked by atmospheric pressure, not by horror vacui. The
two beakers of mercury are connected by a three-way tube as shown, with the upper branch
open to the atmosphere. As the large container is filled with water, pressure on the free surfaces
of the mercury in the beakers pushes mercury into the tubes. When the state shown is reached,
the beakers are connected by a mercury column, and the siphon starts, emptying the upper
beaker and filling the lower. The mercury has been open to the atmosphere all this time, so if
there were any horror vacui, it could have flowed in at will to soothe itself.
Torr
The mm of mercury is sometimes called a torr after Torricelli, and Pascal also has been
honored by a unit of pressure, a newton per square meter or 10 dyne/cm2. A cubic centimeter
of air weighs 1.293 mg under standard conditions, and a cubic meter 1.293 kg, so air is by no
means even approximately weightless, though it seems so. The weight of a sphere of air as
small as 10 cm in diameter is 0.68 g, easily measurable with a chemical balance. The pressure
of the atmosphere is also considerable, like being 34 ft under water, but we do not notice it. A
bar is 106 dyne/cm2, very close to a standard atmosphere, which is 1.01325 bar. In
meteorology, the millibar, mb, is used. 1 mb = 1.333 mmHg = 100 Pa = 1000 dyne/cm2.
A kilogram-force per square centimeter is 981,000 dyne/cm2, also close to one atmosphere. In
Europe, it has been considered approximately 1 atm, as in tire pressures and other engineering
applications. As we have seen, in English units the atmosphere is about 14.7 psi, and this figure
can be used to find other approximate equivalents. For example, 1 psi = 51.7 mmHg. In Britain,
tons per square inch has been used for large pressures. The ton in this case is 2240 lb, not the
American short ton. 1 tsi = 2240 psi, 1 tsf = 15.5 psi (about an atmosphere!).The fluid in
question here is air, which is by no means incompressible. As we rise in the atmosphere and
the pressure decreases, the air also expands.
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