Outside of private school.

Knock knock.

knocked on the door of Du's private school, and Zhang Hao's voice also sounded.

"Sir? Student Zhang Hao came to pay a visit. ”

Behind the door, there was silence.

Zhang Hao touched his head and buckled the door knocker again, "Student Zhang Hao came to see Mr., I don't know if Mr. is there." ”

There was still no response from behind the door.

Zhang Hao wanted to slam the door again.

But as soon as he raised his hand, he heard footsteps behind the door, "It's coming, it's coming, it's like a ghost." ”

After a while, Du Shen opened the door with two dark circles under his eyes.

Seeing Du Shen's tired appearance, Zhang Hao was puzzled: "Looking at Mr.'s appearance, could it be that he couldn't sleep all night?" ”

Du Shen yawned and waved his hand, "yes, I was thinking about how to spend it last night...... No, thinking about how to educate you to become a pillar of the Ming Dynasty, so that you can barely sleep after tossing and turning. ”

Hearing this, Zhang Hao was moved, "Mr. Lao is bothered." ”

Du Shen sweated profusely, and almost said that he leaked his mouth, but fortunately, this stupid and simple apprentice was so easy to fool.

After welcoming Zhang Hao into the house, Zhang Hao walked around like a curious baby, where to look, and finally came to a conclusion that his master life is really simple... Sure enough, it's different from those bewitching sluts invited by my father, and it's a bright and sunny festival...

Du Shen didn't know that he was in the heart of his stupid apprentice, and his image was so tall that he was on a par with Gao Fengliangjie, and after washing his face hastily, he took Zhang Hao to the private school.

arranged for Zhang Hao to sit down, looking at this silly and simple apprentice, but he had a headache.

What to teach, that's the question.

Those who teach Confucianism will definitely not want to be stupid and simple, and if they teach history, it will definitely be even worse, after all, there are some things that cannot be said.

However, Du Shen has always been an ideal and ambitious teacher, and he deeply implements the concept of teaching students according to their aptitude.

What does the apprentice want to learn, just ask no, in case he wants to write some poetry and songs, this thing is so easy, you can fool around when you are a copyist.

Thinking of this, Du Shen smiled, "Apprentice, what do you want to learn?" ”

Zhang Hao smiled and arched his hand: "Students want to learn mathematics, physics and chemistry. ”

Yesterday he remembered clearly, Mr. said that he had learned mathematics, physics and chemistry all over the world, and he was not afraid to go all over the world.

Tut!

I can't imagine that I am still an iron-headed baby, why is it not easy to learn, I want to learn mathematics, physics and chemistry that makes people bald.

This thing makes people bald!

Seeing that his teacher was silent, Zhang Hao shrank his head: "Mr. thinks the students are too stupid, so he is unwilling to teach the students?" ”

Du Shen pursed his lips, you still know that you are stupid: "Apprentice, I want to teach you mathematics, physics and chemistry as a teacher, but now there is a problem, these three private schools are left by your master, you can also see how broken they are, it is not difficult to teach you mathematics, physics and chemistry, but today I can't teach you, our private school is missing something......"

Zhang Hao was curious: "What's missing?" ”

Du Shen smiled lightly: "Chalk, blackboard." ”

Zhang Hao looked confused, chalk? Blackboard?

What is this thing?

What else can I use for teaching?

It's not that he's uneducated, it's that he really doesn't know what these two things are, God is pitiful, he hasn't even used a brush a few times in his life, as for the board? His father had seen a lot of bamboo planks beating him.

Du Shen smiled: "Don't panic, these two things are actually very easy to get, so I'll take you to get a set for the teacher." ”

With that, he took Zhang Hao's shoulders and walked out of the door of the private school.

……

Dujia Village, blacksmith Du Zhuang's house.

The master and apprentice staggered and walked over.

When Blacksmith Du saw it, he couldn't help but be curious, and Weng Li said angrily: "Shenzhi, why did you bring a boy brother to my dirty place?" I'm not afraid of the iron star being hot. ”

Du Shen patted his apprentice's shoulder, and said with a smile: "This is the apprentice I received in Beijing yesterday, it's not a son-in-law, it's just that the family has some spare money." ”

Blacksmith Du suddenly remembered yesterday's situation, and wanted to praise Du Shen a few words, but he was a little embarrassed, so he could only say to Zhang Hao stupidly: "Not bad, it looks like his body is quite good, he is a reading material." ”

Zhang Hao is happy, he likes others to praise him for being a reading material.

Du Shen said again: "To make a short story, I actually came to make something for you." ”

Blacksmith Du patted his chest and said: "What do you want to do, just say, the best blacksmith in the ten miles and eight towns around here is me, and I will definitely do a good job for you." ”

Du Shen arched his hand and said: "What I want to make, in fact, it is also very simple, about five feet long, three feet wide, one side is wrapped in iron sheets, the other side is filled with wooden boards, and the surface is painted with black paint, I call this thing a blackboard." ”

Blacksmith Du is the most hanged blacksmith in the neighborhood, and after a little thought, he knows what to do, and it won't take long.

After all, the blackboard is not a very difficult thing, if it wasn't for Du Shen's lazy hands, he would have done it himself.

made an agreement with Blacksmith Du that he would come to get the blackboard at this time tomorrow, and Du Shen would leave again with his stupid and humble children.

Teaching three-piece set, chalk, blackboard, blackboard eraser, now the blackboard has fallen, the blackboard eraser can be replaced with a rag, but chalk is a little troublesome, except for Du Shen himself, no one else can do it.

The method of chalk is actually very simple, you only need to burn the stone containing calcium sulfate and coal together to obtain relatively pure quicklime, that is, CO2, and then soak it in water, and the precipitated can be used to make chalk.

The stone containing calcium sulfate is generally called limestone, and the scientific name is limestone.

Of course, there are many limestone mines in the vicinity of the capital, but Dujia Village, where Du Shen is located, happens to cleverly avoid those locations, so it is basically impossible to mine limestone.

Moreover, he doesn't have the ability to mine now, think about it.

However, stones containing calcium sulfate do not necessarily have to be limestone, and pebbles in the river can also be used, but there are more impurities, which are not as good as the chalk made of limestone burning paper.

But in Du Shen's words, this thing is similar to a woman and her hands, one is comfortable to use, the other is usable, the former is not to ask for more, then the latter can make do.

To make a long story short, after Du Shen left Dujia Village with Zhang Hao, he went straight to the river, which is the only river in Dujia Village, which is crystal clear, and you can vaguely see fish and aquatic plants swimming in the water, and the source of the well in the village is also the groundwater infiltrated by this river.

While Du Shen told Zhang Hao how to make chalk, he asked Zhang Hao to find some pebbles.

At this time, the sun had quietly climbed into the air, and it was a little hot.

However, there is not much such weather left, it is already the autumn equinox, and it will not be long before winter begins, and then it will be another difficult season.

Du Shen thought about the time when the time came, he should have some grain and rice noodles at home, and thought about whether to make a vegetable greenhouse so that he could eat some fresh vegetables in winter, and then he thought about the greenhouse, and how cold the winter in the north was, and thought about getting a kang or an alternative heating stove in his heart.

But Zhang Hao didn't know that his master was preparing to come out with a rare thing, and he was excitedly picking up pebbles from the river.

As he picked up more and more, he couldn't fit in his pockets, so he simply unbuttoned his robe and wrapped up the pebbles.

That's when ......

A group of people dressed in rushan and tied with square scarves walked towards the river, and looking at them, it seemed that they were running for Du Shen's master and apprentice.