In the summer of the 21st century, getting a glass of iced water is not a difficult task.
Basically, you can buy icy cold drinks at any convenience store on the street.
However, in the ancient Great Song era, wanting to drink a bowl of iced sour plum soup in the summer was not so easy.
One wonders whether this old man's family has an ice cellar, or if they use sal ammoniac to make ice?
The heat-absorbing capability of sal ammoniac was discovered in the Late Tang period; when dissolved in water, it absorbs a large amount of heat, lowering the water temperature and even freezing it.
Since then, sal ammoniac ice-making gradually became a method for producing ice in ancient Huaxia.
Now, hundreds of years later, the technology of making ice from sal ammoniac has become extremely advanced and has been popularized among the common people.
However, sometimes sal ammoniac is not easy to find, so some ordinary households use glauberite—from Old Eight Restaurant—scraped off like that.
