| Historical
Perspective
We
learned for this exercise that another scientist from the 1600'reds was
responsible for  developing our understanding of how gases behave.
Evangelista Torricelli (1608 - 1648) is credited with developing our
understanding of barometric pressure, what causes wind and the invention of
the Barometer. In fact he is honored by having a unit of pressure
named for him, the Torr. He is also credited at measuring the perfect
vacuum often referred to as the "Torricelli Vacuum." That principle is
what were using to make our automatic "water replenisher."
Torricelli, a professor of mathematics in the Florentine Academy, tested
many liquids defining how high a column would remain in a closed end glass tube
when it was inverted in a dish of that liquid. He produced the first
sustained vacuum in his laboratory .
The reason for his experiments was that pumps could only lift water about 30
feet and it was not understood why. These pumps were being used for
irrigation to drain water from mines so it was very important to understand
why this limitation existed. Galileo was commissioned to investigate the problem.
He got other scientists involved in solving this mystery. Torricelli
took a sealed glass tube filled with Mercury and inverted in a dish of
Mercury. He measured the column height (distance BC in sketch right) as 76 cm.
He was credited at understanding that the void above the Mercury column (distance AC) was a perfect vacuum. He realized the height of the liquid
column was the maximum atmospheric pressure pushing on the surface of the
Mercury in the dish could hold-up.
Since
Torricelli
measured a Mercury column being sustained at 76 cm in the tube; he is quoted
at predicting that water would go up 10 m (32.8 feet) on
the basis of the ratio of the liquid densities. (The density
of Mercury is 13.534 gr/cm3 versus water at 1, therefore 76 cm of
Hg actually calculates to 10.29 m of water! That translates to 33.75 feet
not 32.8. feet! 34 feet is the accepted approximate value. Since
scientists of the day were very careful and I suspect weight measurement was
very accurate using a balance he no doubt knew densities accurately enough
to get the number correctly and we're probably just translating the 10 m
from the length measures they used in Italy at the time, the "Florentine
Yard." The Florentine yard is based on the Roman foot. It has been determined that the "Offcial foot is that of Cossutin" and when measuring the length of his foot in a statue it is 0.967 British inches. Therefore the actual 33.75 times 0.967 = 32.6 feet. Therefore that speculation is quite proably correct!
I can only guess what Torricelli and Bernoulli would
think today as they saw most of the world using the very logical base10 metric
(or SI) system of measurement while one of the most "advanced" technical
societies, the USA, is still employing the "foot'' with 12 Inches to the foot
and the yard with 3 feet to the yard and having to use fractions in a
ruler!
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