Two hours later.

Du Shen and the others had already dug out a place half a meter deep, the size of a house, and then he ordered to stop, took out a crude drawing, and let the rest of the farmers start to make the foundation of the academy around, while he took Zhang Hao and the others to rest.

The construction of the workshop was not done overnight, but the academy was even more important to Du Shen.

However, that doesn't mean he doesn't have a chalk workshop.

After taking a sip of tea, Du Shen sat up from the ground, patted his buttocks, and began to walk around the size of the house.

It's not hard to set up a chalk workshop.

Chalk is made of gypsum, which is made of calcium sulfate, and the melting point of calcium sulfate is 700-800°.

If you want to extract calcium sulfate from stone, the only requirement is that the temperature of the furnace should be high, otherwise whether it is a higher content of limestone or less pebbles, it will not be able to be fired sufficiently, and a purer calcium sulfate can be obtained from it.

The first batch of pebbles fired at Du Blacksmith was precisely because of this problem, so Zhang Hao found stones in it at that time.

This is the result of not being high enough, or being unstable.

Therefore, in Du Shen's vision, the stove in the chalk workshop had to be a hearth.

First of all, dig down half a meter, build the wall and roof of insulation with stones or green bricks, set up a stove inside, and then build a ventilation channel around it to ensure that the coal burns more fully, so as to ensure that the furnace, no, it should be said that the temperature of the hearth can be balanced to meet the requirements of refining calcium sulfate.

Thinking of this, Du Shen carried a shovel and drew a rough horizontal line on the ground as he walked.

Zhang Hao and the others were tired with their backs against the earthen wall, panting.

After wielding the hoe and shovel for a long time, their bodies were already wet with sweat, and it was extremely uncomfortable to stick to their clothes, and their palms were blistered.

But everyone didn't complain.

Although several people have never suffered hardship, the beatings have grown from snacks to big ones, and compared to their father's fists and kicks, this is not a problem.

But seeing the strange behavior of their own master, their sluggish spirit was lifted again.

Zhang Hao asked puzzledly, "What is Shizun doing?" ”

Du Shen wiped the sweat from his forehead and explained: "The master is marking the location of the hearth and the vent, and when the time comes, let people build according to the specifications, and the best hearth in Daming can be made." ”

Zhang Hao was most interested in this knowledge, and he asked, "Please solve the doubts!" ”

Zhao Xiu and the others also pricked up their ears.

Du Shen didn't hide his selfishness, and patiently explained the principle to them.

"Do you know why candles burn?"

Xu Pengju blinked his eyes and said, "Because there is a fire fold." ”

Du Shen shook his head and said, "Definitely." ”

Zhao Jin thought for a while and said, "It's because the candle has a wick, and the candle can burn with a wick." ”

Du Shen nodded, but shook his head again, "Yes or no, what you said is just the appearance, but you don't know the deep meaning." ”

As he spoke, he looked at his stupid apprentice expectantly.

Zhang Hao was nervous and thought carefully.

Isn't it because of the wick and the candle itself that a candle burns?

This is a truth that three-year-old children know, why does the master say it is wrong?

Could it be that there is any mystery in this?

Thinking of this, Zhang Hao thought for a while, arched his hand to his master, and said: "The disciple thinks that the reason why the candle can burn should be a chemical reaction, just like calcium sulfate turning into gypsum, but the disciple doesn't know what it is." ”

Du Shen's eyes are full of approval, yes, silly and the longest, and the most attentive one, his impetuousness has been much more restrained, it is rare that he is still good at thinking, I am afraid that he will be the best under the door in the future.

"You are right, the burning of candles is actually a chemical reaction, in fact, in general, everything that burns in this world is in this way."

Du Shen stretched out his hand to compare it to a flame and continued: "What we breathe on weekdays is actually a substance called air, and the air contains many substances, one of which we rely on for survival is called oxygen, people will suffocate to death without oxygen, and the burning of candles is inseparable from oxygen. ”

"If a candle is compared to a substance, then combustion is a chemical reaction between a substance and oxygen, and the flame and smoke it produces are both new substances produced after a chemical reaction."

Zhang Hao suddenly realized: "In other words, the opportunity for the candle to produce a chemical reaction is actually the moment when it is lit." ”

Du Shen bowed his head and patted Zhang Hao's shoulder with a smile.

"Exactly."

Zhao Xiu and Xu Pengju saw that their master valued the senior brother so much, and they all showed envious eyes.

Senior brother only followed the master for a few days before me, and I didn't expect to learn so many things.

It seems that we have to work harder, otherwise, we will definitely be left farther away by the senior brother, and we can only look at his back.

……

North of the Ming border, Shanhaiguan.

Unlike the warm climate in the country, the temperature here is already very cold, and with a heavy rain a few days ago, the temperature is only three or four degrees.

The cold wind whistled the thick fur sweaters of the Tatars.

Dayan Khan's eldest son, Tuluborot, took the reins of his horse from his crotch and looked into the distance with a gloomy gaze.

He has been stationed here for many days, and the dry food brought by the army can't last long, and now that the people in Daming have finished the autumn harvest, it is time to go south.

Moreover, the one he hated, whose name was only one word different from his name, Tulusborot, had also led his army to the border twenty miles away, and could be ahead at any moment.

South......

What a tempting thought.

Tuluborot licked his broad, wind-dried lips, took a sip of the liquor his men had plundered from the Han Chinese, and let out a long roar.

"Behold, Tartar warriors...... The south is the Ming Dynasty, they are rich and weak, they eat fine rice and noodles, drink intoxicating spirits, their women are white and beautiful, and their combat power is vulnerable. ”

Looking greedily at the Ming territory in the distance, Tuluborot raised his horsewhip and ordered: "Kill it!" Plunder their women, rob them of their food, Tartar warriors, stab your scimitars into the chests of these Han Chinese, who claim to be the lords of the East. ”

"Wow!"

"Hohoo!"

Behind him, black-pressed Tartar horsemen surrounded him, wearing leather armor, carrying bows and arrows, round shields in their hands, and scimitars in their right hands, with terrifying expressions that made people shudder.

Since the Tumubao Change, the Ming Dynasty is no longer strong in the minds of the Tatars, but is synonymous with weakness.

They are like a bunch of robbers, never satisfied.