The days when I fished in Daming

Chapter 41

Ancient people made ice in two ways.

The first is the ice cellar in the Xixia Palace in Tianlongbabu.In winter, workers go to the frozen river and lake to collect ice, which must be at least half a meter thick.Hide these large ice cubes in deep underground cellars.There is generally groundwater near the cellar, so the temperature is very low, close to zero.Then the cellar is strictly sealed, and the water is removed regularly, and the rest of the time cannot be entered.In this way, in summer, half of the ice cubes usually melt at most, and the remaining half is enough for the royal family.

The second is chemical ice making.

You are not mistaken, it is chemical ice making, but it was not called chemical ice making at that time.

I have to mention an item called "saltpeter", the main component of which is potassium nitrate. The biggest feature of this thing is that when it meets water, it will absorb a lot of heat, causing the surrounding temperature to drop.

The ancients in China were very smart, otherwise how could they have made the "Four Great Inventions"?

At the end of the Tang Dynasty, people mined saltpeter during the production of gunpowder, and found that saltpeter dissolved in water would absorb a lot of heat, cooling the water to freeze. Since then, there has been a method of making ice in summer.Later, traders gradually added sugar to the ice to attract customers.In the Song Dynasty, there were more and more kinds of cold food in the market. Merchants also added fruit or juice, and even added fruit pulp and milk to the ice. This was very similar to modern ice cream. In other words, it was the originator of contemporary ice cream and even Haagen-Dazs.

In the thirteenth century, Marco Polo brought this ice cream manufacturing method back to Italy, and then to France.A personal chef of Queen Catherine developed a semi-solid ice cream mixed with cream, milk, and spices on this basis and engraved with patterns.
The specific operation is as follows: first find a large basin and pour water into it, then find a small basin and put some water in it.Put the small pot into the large pot.

Please pay attention to one important point, the water surface in the small basin is preferably lower than the water surface in the large basin.Then, slowly pour an appropriate amount of saltpeter into the large basin.When saltpeter meets water, it reacts quickly and absorbs heat.After a while, the water in the small basin gradually turned to ice.

This method was once very popular in the Song Dynasty. After making ice by this method, a cold drink was made.

This shows that the people of the Song Dynasty were very good at enjoying themselves. Although the war was so-so, in terms of enjoying life, few dynasties could compare with the Song Dynasty.

In the poem of Yang Wanli in the Song Dynasty, it is written: Zhuowu is the day of June in the imperial city, and the people in the city sweat like rain.The sound of selling ice comes across the water, and the passers-by don't take it seriously.

However, this method of making ice with saltpeter also has two major disadvantages. One is that the amount of saltpeter used is not cheap, about a ratio of one to one, that is, one kilogram of saltpeter can make one kilogram of ice. Although it can be used repeatedly, it is not easy to popularize.The second is that the quality of the ice produced is average, and it can be used for drinks, but it is not easy to make large ice cubes, so the royal family and nobles can't afford it at all.

Glauber's salt, the name of traditional Chinese medicine.Glauber's salt is a sulfate mineral called Glauber's salt, which is processed and refined crystals.It mainly contains aqueous sodium sulfate (Na2SO4·10H2O).It is distributed in most parts of the country.It has the effects of purging and laxative, moistening dryness and softening hardness, clearing fire and reducing swelling.It is often used in the treatment of stagnation of excess heat, fullness and pain in the abdomen, dry stool, swelling and pain of intestinal abscess, external treatment of mastitis, swelling and pain of hemorrhoids.

This product is prismatic, rectangular or irregular massive and granular.Colorless transparent or off-white translucent.It is brittle and fragile, and the fracture surface is glass-like luster.Slight gas, salty taste.

It can be harvested throughout the year, but it is better in autumn and winter, because it is easy to crystallize due to low temperature.Take naturally produced impure Glauber's salt, commonly known as earth's salt, add water to dissolve it, let it stand to precipitate impurities, filter, heat and concentrate the filtrate, and crystallize after cooling, take it out and dry it in the sun, commonly known as "skin salt".

It is mostly produced in seaside alkaline soil areas, near mineral springs, salt fields and in humid caves.It is distributed in most parts of the country.

In ancient times, there were not many places to find potassium nitrate ore. People mostly obtained it from the soil of old house walls, toilets, pigsty, etc.The soil with more nitrogen elements, due to the action of microorganisms such as bacteria, oxidizes nitrogen-containing organic compounds into nitric acid, and the cations in the soil generally include calcium, magnesium, sodium, potassium, etc., thus forming nitrate.Soils that contain more nitrates are called nitrates.The ancients soaked such nitrate with plant ash water (rich in potassium carbonate), let the potassium carbonate react with calcium nitrate, magnesium nitrate and sodium nitrate to obtain a solution rich in potassium nitrate, and obtained saltpeter (potassium nitrate crystal) after the water evaporated.Because such nitrate is obtained from the soil, it is also called soil nitrate.

Since the sources of nitrate are not abundant, large-scale preparation of nitrate is difficult.Since thenardite can also be obtained from alkaline soil, also known as soil nitrate, and both kinds of nitrate can be used to tan fur, so it is easy for some ancients to confuse the thenardite with sodium sulfate as the main component and the fire nitrate with potassium nitrate as the main component.

Saltpeter, ask Liulichang to buy more, it is not easy for ordinary people, the system is very convenient, after repeated use, it is enough for my own pharmacy to use in summer, it is impossible to make money from this ice making.

But with nitrate, you can try to get some nitric acid to synthesize nitroglycerin. It is not only the raw material for the further development of gunpowder, but also a good medicine for curing diseases.

It is used as a vasodilator in medicine. It is made into 0.3% nitroglycerin tablets and administered sublingually. The effect is rapid and short-lived, and it can treat angina pectoris caused by coronary artery stenosis.

Nitroglycerin tablets should not be swallowed, but placed under the tongue.This is because the swallowed nitroglycerin must pass through the liver during the absorption process, and most of the nitroglycerin is inactivated in the liver, which greatly reduces the efficacy of the drug.There are many blood vessels under the tongue of each of us, which is called the sublingual venous plexus in medicine. Nitroglycerin is very easy to dissolve. When it is contained under the tongue, the dissolved medicine can directly enter the blood, so it not only works quickly, but also the efficacy will not be reduced.The taste of nitroglycerin is slightly sweet and irritating, so qualified nitroglycerin should not only dissolve quickly, but also have a burning sensation under the tongue, which is also a sign that the drug is effective.

Nitroglycerin is mainly used for first aid clinically, and has good therapeutic and defensive effects on coronary heart disease, angina pectoris, hypotension, and congestive heart failure. Nitroglycerin is clinically used as an oral drug and also as an injection.

(End of this chapter)