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Temperature Scale Conversion
Fahrenheit scale
Fahrenheit scale was introduced in 1724 by Daniel Gabriel Fahrenheit
(1686-1736). Fahrenheit was the German physicist and instrument maker
who is famous for first inventing alcohol (1709) and mercury (1724)
thermometers. In order to calibrate invented instruments for temperature
measurement Fahrenheit created his own scale. Very interesting that as
a calibration base for his scale Fahrenheit took three following points
– winter outside temperature, water freezing point and healthy man body
temperature. Fahrenheit simulated winter outside temperature in laboratory
conditions by preparing frigorific mixture of ice, water and ammonium
chloride[+].
This mixture allows to get stable temperature of 0oF (-17.8oC).
[1] Frigorific mixture is a mixture of two or more chemicals that achieve
an equilibrium temperature. The temperature is also relatively independent
of the quantities of mixtures as long as significant amounts of each original
chemical are present in its pure form. A most famous frigorific mixture is
a mixture of water and ice - equilibrium temperature of this mixture is 32oF or 0oC.
Why Fahrenheit took those three “strange” points as base for his scale?
The answer is obvious. At that time devices for weather and medical
observations had a better market. For that reason Fahrenheit created
instrument for temperature measurements in practically applied range.
At the beginning, Fahrenheit took as a basis for his thermometers scale
proposed in 1701 by Ole Romer (1644-1710). Romer scale is based on two
important points. Brine freezing point and water boiling point
(0 and 60 degrees according to Romer scale)[+].
[2] Ole Christensen Romer was a Danish astronomer who in 1676
made the first quantitative measurements of the speed of light.
[3] Why Romer took 60 degrees difference between two important points of his temperature scale? First of all Ole Christensen Romer was a prominent astronomer –as we know in astronomy sexagesimal system is very important and astronomers have been using it about four thousands years science Babylonians took sexagesimal system from their every day life to astronomical observations. 60 seconds in minute (time and angel) , 60 min in one hour and 60 minutes in one degree (angle). [4] Brine is water solution saturated or nearly saturated with Sodium Chloride (NaCl). At the concentration of 23.3% freezing point of the solution is -21°C or -5.8°F.
In order to avoid negative temperature Fahrenheit took as zero point the
temperature of frigorific mixture (-17.8oC) and measured temperature of
water freezing point and healthy man body temperatures applying Ole
Romer scale. Measured by that way temperature of freezing water was
equivalent to 7.5o and temperature of human body was equivalent to 22.5o.
Fraction numbers like negative temperature didn't fit Fahrenheit demands
[+]
and he multiplied the scale by 4. Eventually, Fahrenheit set water
freezing point as 32o (7.5x4) and human body temperature as 96 (he altered
this point from 90=22.5x4 to 96).
[5] Meteorological measurements were the main field of Fahrenheit interests on the one
hand and specific demands of market on the other. Taking it to account we understand
that Fahrenheit proposed very intelligent and convenient scale without negative
temperature and fractions. Providing further scientific researches Fahrenheit produced
thermometers for liquid boil points measurement up to 600°F (675°F is mercury
boiling point). But devices for measurements in range higher than 130°F hadn't
market and consequently wasted (~130°F is temperature of human body suffering from fever).
Those who are used to Celsius scale and decimal system have reasonable
question – why on earth Fahrenheit set hight point exactly 96o? There were
a number of reasons. Let's say we take thermometer and mark lowest
point-which is 0o, second known point – 32o and highest point - alcohol
expands up to this point when it is held in the mouth or under the armpit
of a healthy man until liquid has completely acquired body heat. The
distance between 0o and 32o marks is equal to half of distance between
32o and highest point, at the same time it is one third of distance between
0o and highest point – in this case 96 is most convenient mark for highest
temperature point. On the other hand, at that time Europe used Imperial
measurement system
[+]
- 8, 12, 16 are some kind of “magic” numbers and
96 can be divided by these numbers without fractions.
[6] Measurement system of middle age Europe slightly differed between countries but
generally take its roots from measurement system of Roman Empire. Despite the difference
in units, general proportions was kept – like one inch is 1/12 of foot, one ounce is 16
dram and 1/16 of pound, one pint is 1/8 of gallon and so on. The expression “Imperial units”
actually is derived from Roman Imperial Measurement System spread around Europe in ancient
ages by Romans and brought later to Australia, India and American continent by Europeans.
Later, this contradiction point was revised by other scientists to 98.6oF. They simply divide the scale between 32oF and 212oF (freezing and boiling points of water) by 180 parts – it allowed to determine more precisely the point marked by Fahrenheit as 96o.
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