00:00Imagine eating ice cream in a 40-degree desert 2,000 years before electricity was even a
00:05concept.
00:05It sounds like a magic trick, but ancient Persian engineers were actually masters of
00:09thermodynamics, long before we even had a name for it.
00:12So the first big question is where did they even get the ice from in the first place?
00:15The answer is that they used a unique classic climate to their advantage.
00:19During the winter when temperatures fall at night, they would flood shallow pools with
00:22fresh water.
00:23Because the desert sky is so clear and dry, heat from the water would radiate directly
00:27out into space through a process called radiation, causing the water to freeze even if the temperature
00:31was slightly above freezing.
00:33By morning, they had sheets of ice ready to be harvested and rushed into storage before
00:37the sun could get too high.
00:38But once you have the ice, how do you keep it from melting in a giant pile?
00:41The answer is a structure called a jack shell, which literally translates to an ice pit.
00:45These were giant dome-shaped buildings with massive underground storage pits that could
00:49hold up to 5,000 tons of ice.
00:50You might ask why does the jack shell look like a giant cone?
00:53The answer is that the dome-shaped was a clever way to manage heat, as the air inside warmed
00:57up.
00:57It would naturally rise to the top and escape through a vent at the peak, while the goodest
01:01air stayed trapped at the bottom with the ice.
01:03This leads us to our next question, what could they possibly build these out of what they
01:07wouldn't just bake in the sun?
01:08These engineers used a super-motor called Saroj, which was a mix of sand, clay, lime,
01:12and ash, combined with some surprising ingredients like goat hair and egg whites.
01:16These created walls that were up to 6 feet thick and were almost completely heat-proof and waterproof.
01:20Some historians even say the domes were covered in thick layers of star-thatch to act like
01:24a giant fuzzy blanket, keeping the desert heat away from the treasure inside.
01:27Was the insulation enough on its own?
01:29Not quite, so how did they actually keep the interior cold during a heat wave?
01:33They used windcatchers, which were tall towers that caused the desert breeze and funneled
01:37it down into underground channels.
01:38Often these tunnels were connected to canthas, which were underground canals of cold mountain
01:42water.
01:43As the hot air passed over the water, it went through a process called evaporative cooling.
01:47This is the same reason you feel cold when you step out of a shower.
01:50As water evaporates, it requires energy, which it takes away from its surroundings as heat.
01:54This dropped the temperature inside the ejection to fridge levels, keeping the ice frozen even
01:57when it was 40 degrees Celsius outside.
02:00Did any other civilization have their own version of a fridge?
02:03Ancient Egyptians used a much smaller version of this same cooling trick called the port-import
02:07system.
02:07They would put a small clay pot inside a larger one, fill the gap between them with wet sand,
02:12and cover it with a damp cloth.
02:13As the water in the sand evaporated through the porous clay, it stirred the heat out of
02:16the inner port, keeping food fresh and water-cooled in the middle of the desert.
02:19So why does all of this ancient tech matter today?
02:22It shows that humans have always been incredibly good at solving problems using the environment
02:26around them.
02:27These ancient refrigerators were sustainable, energy-efficient, and worked for thousands of
02:31years, without ever needing a power pit or a refrigerant.
02:33Next time you grab an ice cube, just think about the desert in genius, overdoing the exact
02:37same thing with nothing but mudwind and egg whites.
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