Accidentally dressed as an empress

How was ice made from saltpeter in ancient times?

First of all, there are two types of saltpeter. One is saltpeter, potassium nitrate, which is the raw material for making gunpowder and fertilizer.

The other is Glauber's salt, sodium sulfate decahydrate, which is produced in salt lake salt springs. It is a medicinal material that has the effects of purging bowels, clearing heat and reducing swelling.

If you mix up the raw materials in the first step, it will be difficult to make ice successfully.

Because the heat absorbed by sodium sulfate decahydrate when it dissolves in water is different from the heat absorbed by potassium nitrate when it dissolves in water.

Sodium sulfate decahydrate can only cool water, but it is difficult to reach zero point and freeze the water into ice.

However, the heat absorption effect of potassium nitrate is better than that of sodium sulfate decahydrate, and the heat absorption is very obvious.

But the question is, how much potassium nitrate is needed to freeze water?

The saltpeter ice making process typically involves dissolving potassium nitrate in a larger container, which is then placed inside a smaller metal container with good thermal conductivity. However, two conditions must be met: first, a large amount of potassium nitrate must be poured in all at once and stirred vigorously to dissolve it quickly; second, the water temperature must be relatively low.

Modern data show that at room temperature, potassium nitrate aqueous solution begins to feel noticeably icy when the solid content is 5%. When it exceeds 20%, it cools rapidly and begins to freeze and solidify. After solidification, it will continue to cool to below 0 degrees Celsius.

However, ancient saltpeter contained impurities, and there was no effective way to purify potassium nitrate. Using a 1:4 ratio of saltpeter to water likely wouldn't lower the temperature.

Therefore, the solution is, first, to increase the ratio of saltpeter to water, using a ratio of 1 to 3, or even higher.

Second, lower the water temperature and use well water with lower temperature.

Third, increase the amount of saltpeter used to create economies of scale. A three-foot-thick ice doesn't form overnight. Can 100 grams of potassium nitrate freeze 400 milliliters of water? Experiments show that it can't.

But 1 kilogram of potassium nitrate should be more than enough to freeze 4 liters of water.

But in fact, it is difficult to find so much saltpeter.

When saltpeter ore is mined, saltpeter can be precipitated by low-temperature crystallization. In this process, ice is produced incidentally and serves as a byproduct in the production of saltpeter.

To make ice, you have to find saltpeter mines first. But saltpeter mines are not like cabbages, it is not that easy to find them.

According to the system recording, Ren Li purchased saltpeter from the saltpeter farmers.

Saltpeter farmers obtain saltpeter by sweeping the white frost formed on the earthen walls in front of and behind their houses.

In the clear and crisp autumn weather, saltpeter usually precipitates in the form of salt flowers, covering the ground and corners of walls. This is called ground frost.

Ground frost is widely distributed at the base of walls near pig pens, stables, toilets, the base of walls of old houses, cliff edges, and in caves.

Saltpeter miners sweep up the saltpeter-containing soil, place it in a container, and soak it in water. After filtering, the filtrate is boiled or dried to obtain saltpeter crystals.

The clever saltpeter people also mastered a way to make more saltpeter. They would find a ceramic jar, mix wood ash and saltpeter soil together, heat it, and let it cool naturally to precipitate the saltpeter.

The main principle is to use the potassium ions in wood ash to replace the sodium ions in nitrate soil to produce potassium nitrate.

The saltpeter produced by the traditional method of making saltpeter is still not enough for making ice, but it is enough to cool the water and achieve the effect of ice.

Although she failed to make ice, Ren Li did produce a lot of saltpeter solution. She organized people to filter the solution with linen gauze, then heated it to evaporate the water, allowing the saltpeter to precipitate, and extracted a lot of saltpeter.

Ren Li wasn't one to stick to her guns, so she simply sold saltpeter, which sold quite well. Saltpeter could be used to make fire sticks and fireworks.

Ren Li temporarily gave up making ice from saltpeter. She stayed at Wang Yuan's house and discovered that Wang Yuan stored ice in the ice cellar during the winter.

Inside the Wang family's ice cellar, ice blocks formed a single wall, leaving no gaps between them. A thick layer of insulating linen cloth covered the ice, and then a layer of bricks and stones sealed it off to isolate it from the outside heat.

After storing the ice in winter, the entrance to the cellar is sealed with yellow mud and bricks and stones. The ice can only be taken out during the hottest days of summer.

After opening the cellar, the ice in the cellar must be used up quickly, otherwise it will melt quickly.

Ren Li bought the ice from a cellar of the Wang family and transported it to Lingyun City, but encountered difficulties during the transportation process.

There was really no thermal insulation material in ancient times.

Ren Li wrapped large blocks of ice in hay and linen and transported them out of the city in a horse-drawn carriage.

She sprinkled water on the outermost layer of linen, hoping that the water would evaporate and take away the heat, but the ice still melted quickly. She set out at dawn and arrived in Yunyang City before noon.

Finally, Ren Li decided to sell it in Yunyang City, because it would be impossible to reach Lingyun City and the ice would melt completely.

In Yunyang City, Ren Li once again encountered the dilemma of the wealthy families not needing ice and the common people not being able to afford it. She made some inquiries and sold the ice cheaply to the wealthy Shen family, who did not have an ice cellar at home.

She didn't make any money this time, so she had to buy Yunyang City's specialties, linen and ramie cloth, on the recommendation of the Shen family, and brought them back to Lingguan City to sell.

Every household in Lingguan City planted mulberry trees and raised silkworms, making silk very easy to come by. Linen and ramie were looked down upon. With Ren Li's goods piled high, he took the silk from Lingguan City with him and traveled to other cities to sell it.

Her destination was Lingyun City, which was of course right under the emperor's feet, so the goods could be sold at a high price.

Yunxiu finished reading Ren Li's recent situation. Ren Li was relatively worry-free, so she could put her mind at ease for the time being.