Fu Rui watched as the two men approached with a load of salt each, directing them to fall aside. According to Du Zhongxiao's instructions, he poured the soil salt into a large pot and turned it into salt water. After pouring more than a dozen loads of salt water, the salt water was saturated, and then the salt water was scooped into the empty pot next to it.

Du Zhongxiao saw that it was almost full, and ordered Tao Seventeen to take someone to light the coal under the pot.

One or twenty salt supervisors, Kuzi, Douzi and others stood listlessly on the side, watching Du Zhongxiao directing people to be busy, with expressionless faces and blank expressions. In the last year or two, the salt prison has been sluggish, and their lives have been difficult, and they have lost interest in everything.

This process was extremely long, and Du Zhongxiao saw that the fire was burning, so he went out of the shed and went to the official hall to talk to Feng Yuan and the others. Whether it is refined salt or boiled nitrate, it is now a technical secret and cannot be seen by outsiders. This industry has become big, there are many uses, salt is still a trivial matter, all kinds of by-products nitrate and alkali, will be of great use in the future, once it is introduced to the Khitan, there will be hidden dangers.

The north of the state and the Khitan field are in Yanmen Village, because the Khitan prohibits the city of horses, sheep is the largest export material of the Khitan. In addition to the tens of thousands of live sheep every year, there are also large quantities of sheepskins, as well as a small amount of other animal skins.

Feng Yuan was very familiar with the area of Yanmen Village, and told Du Zhongxiao about the geography and people there, as well as some interesting things about his own business.

Seeing that it was almost noon, Du Zhongxiao ordered someone to serve two wines, and he returned to the place where the salt was boiled.

Let the person who boiled the salt try the boiling brine, and found that there were already salt crystals at the bottom, Du Zhongxiao instructed someone to scoop out the boiling brine and pour it onto the cloth erected with a wooden frame next to it, so that the filtered brine was poured into the pot below.

To refine salt, the process is nothing more than evaporation, filtration, and crystallization. However, although the cloth is simple, the specific operation has a lot of exquisiteness, and the more fine the salt obtained, the more sophisticated. If there is no filtering and crystallization behind, and the water is boiled dry directly in the pot, what you get is the soil salt in the salt field, which is of poor quality, contains too many impurities, and is inedible. For example, the salt water filtered into the pot can still be remade again, and it will be done three or five times before you get the fine salt of the snowflakes.

However, today Du Zhongxiaozhi is not refined salt, but nitrate in soil salt, so this step is omitted.

After all the boiling salt water was filtered, Du Zhongxiao ordered someone to take the cloth for filtration. I saw a thick layer on it, white as mud, and there were a lot of them.

When Fu Rui saw it, he hurriedly said: "This cloth is blocked, it is unusable, hurry up and replace it with a new cloth!" ”

Du Zhongxiao said with a smile: "The governor thinks badly, what we want is the white mud on the cloth." You come with me, but you wash the white mud with water several times, and then steam it out, like snowflakes, which is the nitrate we want. ”

Fu Rui was curious, walked up and looked at it, and said, "Is this nitrate?" I don't know what nitrate is? ”

Du Zhongxiao said: "This is manganese." Where salt is made from brine clay, when the first salt is made, alkali and nitrate are harvested, but most of the nitrate at that time is fire nitrate. The soil salt turns into salt water, boils it again, and what comes out is miscanthus salt. This is the difference in physical properties of miscanthus nitrate and fire nitrate, and the production is different. ”

In the past, when he was in Yongcheng, in order to make fire nitrate, Du Zhongxiao studied the chemical properties of saline-alkali soil, and he was no stranger to it. In the process of making salt from saline soil, the first step is alkali sodium carbonate and a part of potassium nitrate. By refining them, it is possible to separate the two, and the technology of this era is very mature. Finally, the salt is refined, and what comes out is sodium miscanthus sulfate. The composition of saline-alkali soil is different in different places, and the proportion of these three by-products is also different. Here in Bingzhou, the most by-products are miscanthus nitrate and fire nitrate, and the alkali is less than that in Bozhou.

In fact, the production of soil salt in this area of Hedong has not been cut off in history, and with the development of gunpowder technology, the importance of fire and nitrate has become higher and higher. So much so that during the Anti-Japanese War in history, salt became a by-product of fire and nitrate, and the output was very huge at that time. Du Zhongxiao didn't know this history, but he had realized that the value of soil salt on Hedong Road was not in the salt itself, but in its by-products. In particular, Hedong Road also produces sulfur, and the conditions for producing gunpowder are much better than those in Bozhou, and even at this time, the Song Dynasty's ban on the Khitan list has fire and sulfur.

Fu Rui felt curious, and took a few manpower to go out to refine the collected manganese. At this time, the composition is relatively simple, and after several filtration and crystallization, a suitable product is obtained. It's just white with a slight yellowish tinge, which is far from snowflakes.

Du Zhongxiao saw it, wrapped it in a cloth bag, and took it to the official hall.

opened the cloth bag and let Feng Yuan and the others see the manganese inside, Du Zhongxiao said, "How?" This is made from soil salt, and it is best used for tanning skin. This thing is forbidden along the border, and it is not common on the Khitan side. Of course, the most important thing is that there is a lack of craftsmen there, and the leather is cooked, so it still depends on us Han people. No matter how many skins you sell, I can recruit craftsmen here and finish the tanning. ”

Feng Yuan took the cloth wrapped in his hand, passed it to the other two, and twisted a little bit to taste it in his mouth, and nodded again and again: "Sure enough, it's manganese." ”

Du Zhongxiao smiled silently, miscanthus and many similar compounds are slightly astringent and salty, where can I taste it?

Seeing that Du Zhongxiao had made a lot of money without much effort, Feng Yuan was determined in his heart, and said in his mouth: "Since the officials can make nitrate here, they can recruit skilled craftsmen to start this business." In fact, in the area of Hedong, not only in the city, but also in the countryside, there are good leather-making craftsmen, and craftsmen are not scarce. The difficult thing is that someone builds a property and makes this business bigger. ”

Du Zhongxiao said: "This matter is not difficult. As long as there are many people who know this craft, even if they are assigned to the errands, I will find enough people. What is lacking is that you will sell enough furs, and when they are ripe, they will be sold in other places. ”

Feng Yuan said with a smile: "The cooked leather can not only be sold to the Central Plains, but also to the Northland. The officials didn't know that those Khitan nomads, in order to prevent the cold, wore leather jackets made of raw hides, which were hard and uncomfortable, and easy to damage. With cooked skin, who will wear raw hides? ”

Making leather with nitrate tanning is actually not a great craft, but in this era, the number of people who can master it is still limited. In particular, there was no habit of wearing fur in the Central Plains, and the development of technology was slow. However, in the area outside the Saiwai, there are few craftsmen and do not have the conditions for industrialization.

Seeing the real thing, Feng Yuan no longer doubted it, and said to Du Zhongxiao: "Since it is not difficult to make nitrate, then all the furs on my ship will be tannified locally. After we have finished eating, we will go to the skilled craftsmen with the officials to see if it is good to do it. ”

Du Zhongxiao has no objections. Hedong is vast and sparsely populated, not to mention that there are many sheep raisers, even the hunters in the mountains are also a lot, and there is no shortage of people who can tann leather. The hides are tanned for only a few days, so they are not too troublesome.

Just when Du Zhongxiao and Feng Yuan were talking enthusiastically, Fu Rui came in with a bag of salt and said to Du Zhongxiao: "Look at the judgment, the salt we have refined is as white as snow, no worse than the salt solution in the south." It is not difficult to sell in the city in this condition. If all the salt in the field is refined, it may be sold. In the past, it was difficult to sell local salt, but the quality was too poor and the price was high. ”

Du Zhongxiao looked at the refined fine salt and nodded. In fact, there is a reason for the existence of soil salt here in Hedong, although it is made from scraping and drenching in the soil, there are not many impurities after refining. At a time when the cost of salt transportation is the lion's share, prices are competitive.