For the next few days, Xu Chen ate and lived on the island.

When they went to Xu Fan's class for the second time, Xu Chen and the others proposed to the teacher that they would not go to class for more than ten days. Xu Fan also knew that Xu Chen and they needed to make some preparations for the trip to Changshan Island, so he let them go.

In the spare time from practicing water warfare, Xu Chen mobilized the teenagers to clean up the guano that had accumulated on the island for many years, and built a few thatched huts on the shore. Xu Chen is going to use this small island as a secret base for himself in the future, and put some things that cannot be seen by everyone here, such as gunpowder and glass.

The main components of gunpowder are sulfur, charcoal, and fire, charcoal and sulfur are relatively easy to obtain in Yuzhang City, and as for fire, it depends on the dung in front of you.

The chemical name for fire elimination is potassium nitrate. Nitrate soil and plant ash are the raw materials used to make potassium nitrate. Usually in the soil near pigsties, toilets, etc., in the countryside, there is usually a lot of organic matter. After the decay of these organic matter, nitric acid can be formed through the chemical action of nitrifying bacteria. Nitric acid further reacts with potassium, calcium and magnesium in the soil to produce potassium nitrate and calcium and magnesium nitrate, which is soil nitrate. The amount of potassium nitrate in different soil nitrates varies, usually only a few percent.

In addition to toilets, pigs, and cattle pens, nitrate soil is generally found at the foot of old walls in courtyards, cliff edges, caves, and floors that are not easily washed by rainwater. The nitrate soil is damp, not easy to dry, slightly purple-red after being exposed to the sun, and a good nitrate soil will burst out on the burning charcoal.

As for the method of making soil nitrate, Xu Chen used the method used by the Eighth Route Army back then.

First of all, the nitrate soil and plant ash are ground and crushed separately, and then the raw materials are weighed according to the ratio of eight to one of the nitrate soil and plant ash, and mixed into a large specially built pool. Then put in hot water about 70 or 80 degrees, and after the water surface can be soaked in the raw materials, then stirring and filtration. The whole process lasts about one to two quarters of an hour, and finally the slag is removed and the water is retained, and the filtrate obtained is nitrate.

Then put the nitrate water into ten large urns, heat and evaporate, this process is commonly known as "boiling nitrate". Stir constantly while heating to prevent sticking and splashing. When two-thirds of the water has evaporated, the firewood is pumped out and the heating is stopped. Take a small amount of mucus drops on the paper, if you see the mucus condensing into a clump, it is to meet the requirements. At this time, it must be immediately hot, and then add water again to suction filtration.

Finally, after the filtrate is naturally cooled, the potassium nitrate crystals can be obtained by suction filtration again. However, this is only crude potassium nitrate crystals, in order to get a relatively pure nitrate, it is also necessary to reheat and filter once to remove the impurities. When the potassium nitrate crystals are cooled and recrystallized, the white crystals, which look very similar to salt to the naked eye, are pure fire nitrate that meets the requirements, and can be used as a raw material for gunpowder.

With this method, Xu Chen was able to turn the thick guano on the island into a weapon of war. It's just that it's impossible to make such a big move undetected, and how to hide it from people still needs to be well planned.

Through these days of training, the teenagers gradually began to get rid of their jerkiness, and the handling of the boat became much smoother. After a few days of training, there was a gap between the teenagers, and they began to adjust themselves, and leaders began to appear in the team to guide the team members' training.

This is also the effect that Xu Chen wants to achieve, the boys train by themselves, see the strengths of others and their weaknesses, and willingly accept the leadership of the captain. This is more convincing to the teenagers than Xu Chen's simple and rude appointment, they are all young and vigorous, and Xu Chen doesn't want to hurt the heart of even one of the teenagers for this little thing. Although the speed has slowed down significantly, if Xu Chen wants to go further, this time must be willing to spend.

In the past few days of training, a captain and a co-o'clock have appeared on each ship, which is also the practical application of the teenagers based on some of the knowledge taught by Xu Chen.

Because it was just a modified ship, Xu Chen didn't plan to use it for long, so he didn't name the ship, and it was uniformly numbered as No. 1, No. 2, and No. 3 in order.

At present, the captain and deputy of the No. 1 ship are Lu Hao and Shi Lei, the No. 2 ship is Wang Tieniu and Zhou Kang, and the No. 3 ship is Zheng Tai and a teenager named Shen Yuan.

The best training is not the boat of the second and third children, but Zheng Tai's boat, this Zheng Tai is really talented in water fighting. When Xu Chen told the teenagers about the ocean and other countries, the rest of the teenagers showed more shock and curiosity about those anecdotes, and after the shock on this Zheng Tai's face, he showed a strong desire and a fiery ambition in his eyes.

None of the teenagers doubted the words of their eldest brother, even if Xu Chen told them that the land where we live was round, the teenagers were only surprised for a moment and accepted it. On the one hand, it is their unconditional trust in this magical big brother, and on the other hand, because they have not received any orthodox education, the words of the saints in the round world are very unfamiliar to them, and the knowledge they receive comes from their eldest brother, so naturally they will remember what Xu Chen says.

This is also the reason why most of Xu Chen's cronies around him in the future are orphaned teenagers, although the cultivation cost is a little larger, and the cycle is a little longer, but the effect is quite significant, and it is also convenient to transfer alone.

After seeing Zheng Tai's ambition, Xu Chen took him to a small black room in the backyard.

When the lights in the room came on, Zheng Tai was shocked by a huge map hanging on the wall, the map on the wall was drawn one big island after another, using the eldest brother's lecture to understand that it was the mainland, our Datang is also on a continent, just on the right side of the largest continent in the upper left of the map, the word "Datang" written with a black pen is prominently displayed.

Zheng Tai was only an orphan before this, his young age limited his leg strength, and it was impossible for him to travel far away without any money, and he had only begged in Yuzhang City and a few nearby counties all his life. Ever since he heard his eldest brother talk about the outside world, he had developed a strong interest in the distant and vast world, and a hazy thought took root in his mind. He dreamed of one day being able to swim in the boundless sea that his eldest brother said, and to that strange country to see different customs.

When he looked up and saw the map on the wall, the yellow represents the continent, and the dark blue represents the ocean, sure enough, as your eldest brother said, the ocean is so vast, much larger than the continent, after seeing this map, Zheng Tai felt that his breathing had stopped, and the thoughts in the depths of his mind came out strongly again, and this time he felt that he was so close to his dream. He had decided that his destiny in this life would be on this boundless sea.

The map on the wall was drawn by Xu Chen according to his memory, and here Xu Chen really wants to thank the geography teacher in high school, the perverted teacher actually asked everyone to accurately draw the outline of each continent and the direction of the ocean currents, as well as the map of the administrative divisions of each province in China, Xu Chen spent several days to complete the homework, and this teacher actually gave seventy points.

Fortunately, in the Tang Dynasty during the Tianbao period, this is definitely the most accurate map in the world, there is no one!

With a map of the world, it is very simple to make a globe, go to the calligraphy and painting shop to consult the master, and people in ancient times also pasted pictures on round objects for entertainment. In particular, Yuzhang County is the hometown of ceramics, and then paint after burning ceramics, which is the practice of rich and noble families, in the workshop of small households, the pictures will be drawn in advance, and then printed one by one after the ceramics are burned. Spherical ceramics are naturally not uncommon.

Drawing the map in an arc, cutting it in half from the middle and putting it on the ball polished by the tree nodules, a simple globe was ready, and then marked with latitude and longitude, Xu Chen felt that what he had done was definitely better than the stalls sold in later generations. After Xu Chen made the glass in the future, he could start to make a sextant, with the Stallone version of the prison break, there is no reason why people can't make things with a few pens and a pair of glasses.

The sextant in memory has a fan-shaped shape, and its components include a small telescope, a translucent and semi-reflective fixed plane mirror, known as a horizon mirror, and an active reflector, known as an indicator mirror, linked to the indicator. The scale arc of a sextant is one-sixth of the circumference. When used, the observer holds a sextant and rotates the indicator mirror so that the celestial objects that appear at the same time in the field of view coincide with the sea horizon. The altitude angle of the object can be read according to the angle of the indicator mirror.

As soon as the sextant is built, who else is Xu Chen's opponent on the ocean, what kind of astrological trick in Arabia is simply rubbish compared to this.

When Zheng Tai recovered from his shocked state, Xu Chen handed him the globe and a book, which were some of the nautical knowledge and naval battles that Xu Chen had summarized these days, and as for the rest of the country's style and the like, Xu Chen would teach them together when he gave lectures to the teenagers, and today this is a small stove for Zheng Tai.

"From now on, you will have an hour every day to come to this room and read. But I can only memorize, I can only memorize, I can't take things out of this room. Remember!" Xu Chenyan advised.

No way, the things in this room are so amazing, even if it is my own brother, I have to tell it.

"Big brother, don't worry, I understand!" Zheng Tai is also a smart person, so he naturally understands what the eldest brother means.

After these days of study, Zheng Tai really did not disappoint Xu Chen, and soon mastered the essentials of water warfare. He numbered everyone, including himself, and divided a dozen young men into different groups, one for rowing, one for the helm, and others for raising and lowering sails, handling trebuchets, and throwing javelins.

Although these teenagers will need to learn these subjects in the future, they have to train specifically for the sake of efficiency.

Following Zheng Tai's example, the other two ships began to follow suit. Soon the teenagers completed their basic training and began their actual combat drills.

Xu Chen simply handed over the command to Zheng Tai, and he gave him specific command.

So, under the command of Zheng Tai, the three boats were divided into two groups, and Zheng Tai and they started the confrontation drill in a one-on-two, and for a while, the water surface was "full of smoke", and the three boats began to chase, collide, connect and other water battle actions on the water surface on the shore.

For the next few days, the boys practiced day and night on the shore as the New Day of August was approaching......