After seeing the villagers off, the group went into the tent and sat down to discuss the next steps with Qiao Lizheng.

What Qiao Lizheng couldn't understand was that this time, Marquis Zhengyang had mobilized a large force to investigate the deaths of children in the village, not to conduct an in-depth investigation in the village, but to lead these thousand soldiers up the mountain to search for some kind of mineral.

Zhao Xian also asked that someone familiar with the mountains be found to guide the soldiers.

Qiao Lizheng didn't dare to ask any more questions. Since Marquis Zhengyang had made such an arrangement, he must have his reasons.

Before long, twenty able-bodied young men were brought from the village. They were all locals and very familiar with the situation at Fudu Mountain.

Zhao Xian divided the thousand soldiers he brought into twenty small teams, each led by a young and strong man, and set off for Fudu Mountain to search for saltpeter mines.

Because Fudu Mountain is too large, Qiao Li is dividing the entire Fudu Mountain into twenty areas according to Zhao Xian's request, and assigning a small team to each area to search for saltpeter mines.

Zhao Xian set up a camp on the mountain and arranged for people to test the mined ore. They put the ore samples into earthenware jars containing scorpions and observed the scorpions' reactions.

To keep the scorpions active, Zhao Xian ordered his men to heat the area around the tents to raise the temperature inside, but only on the condition that no smoke enters the tents.

The samples brought by the soldiers were all rocks carved out from below the surface of the mountain. They knocked off a piece of rock and put it in an earthenware jar to observe whether the scorpions reacted.

They tested many stones and found that the scorpions did not react, indicating that these were just ordinary stones.

Finding saltpeter is not so simple; one must be focused and search diligently. And so a day passed, and they found nothing.

The search for saltpeter continued until the afternoon of the third day, when a soldier brought a stone that was somewhat whitish and contained some gray crystals.

No one paid much attention. They chipped a small sample off the rock, put it in the earthenware jar, and observed the scorpion's reaction.

At first, the scorpions didn't react, but after a while, they became restless and started crawling around in the pot, trying to get out.

"It moved! The scorpion is trying to escape. This rock must be saltpeter," Li Xue said excitedly.

Zhao Xian took the stone out of the earthenware pot, and the scorpions finally quieted down.

"Where did you get this stone?" Zhao Xian asked.

"Reporting to Marquis Zhengyang, it was collected from a cave. The cave is very deep and damp inside," a soldier replied.

"Okay, continue to collect more stones from the cave to expand the quarrying area."

"Yes, ma'am."

After the soldier finished speaking, he quickly left.

"Brother Zhao, is this really saltpeter?" Li Xue asked.

"It's not certain yet; we need to continue verifying. Hopefully, this is the saltpeter we're looking for."

After Zhao Xian finished speaking, he continued with the next experiment. Li Guang and Li Xue stared at him, wondering what he would do next.

In fact, Zhao Xian could easily have solved the problem using test strips, but with so many people watching him, he still had to use the ancient method to test.

Zhao Xian broke the stone into small pieces, put them into the bottle, put a pre-prepared pig bladder over the bottle opening, and then heated the bottle.

If the stone is saltpeter, it will release oxygen when heated to over 300 degrees Celsius. At that time, people did not know what oxygen was, but they already knew how to use this method to discover saltpeter deposits.

Under everyone's watchful eyes, the pig's bladder began to swell, growing larger and larger until it collected a considerable amount of gas.

Seeing that he had collected enough gas, Zhao Xian removed the pig's bladder, tied it tightly, and prevented the gas inside from escaping.

Then, Zhao Xian went outside and fetched a few pieces of burning firewood, which he put into an earthenware pot. The flames of the firewood quickly went out, leaving only thick smoke and sparks, as if it were about to go out.

Seeing everyone staring at him with curiosity, Zhao Xian spoke:

"If the gas from the pig's bladder can reignite these firewood pieces, it proves that the stone is saltpeter."

Finding the saltpeter led to the discovery of the cause of death for the children in Fudu Village.

Zhao Xian's words raised everyone's expectations. They hoped the experiment would be successful, since they had already been on the mountain for three days.

The pig's bladder contained collected gas. Zhao Xian opened the outlet of the bladder, and the gas inside sprayed into the smoking firewood in the earthenware pot.

A miraculous scene unfolded: as the gas spewed out of the pig's bladder, the firewood in the earthenware pot suddenly burst into flames, stunning everyone present.

The crowd cheered; they had finally found the saltpeter.

Next, the group headed to the cave where they had found the saltpeter mine. The cave was very well hidden, with only weeds and rocks at the entrance, suggesting that few people had ever been there.

At this moment, the soldiers were clearing weeds and rubble from the cave entrance when they discovered a clear spring gushing out of the cave and slowly flowing down the mountain.

At this moment, Qiao Lizheng also arrived. He looked at the cave and said:

"The villagers are familiar with this cave. Because it is located in a remote place, it is gloomy all day long, and wild boars and wolves roam around. The villagers rarely go near it, let alone dare to enter the cave."

Surprisingly, this cave turned out to be a saltpeter mine. Could the deaths of children in the village be related to this saltpeter mine?

Zhao Xian looked at Qiao Lizheng with a serious expression and said:

"Joe is checking what's flowing out of the hole."

Qiao Lizheng took a closer look and thought, "What's so special about this? It's just spring water."

"Is the Marquis of Zhengyang referring to the stream flowing from the cave?"

Zhao Xian nodded and said, "Qiao Lizheng, take another look at where this stream flows to."

Qiao Li was walking along the stream, with Zhao Xian and the others following behind. After walking for a while, they could see the scene below the mountain.

Below the mountain is Fudu Village. The mountain is not very high. The stream flows along the hillside towards the village and eventually merges into the ponds next to the village.

Qiao Lizheng seemed to be deep in thought. He stared at the stream for a long time, as if he had understood something.

"Lord Zhengyang is saying that this stream flowing into the village is the culprit that caused the deaths of the village children."

"You can think of it this way: we've confirmed that there's a saltpeter mine in this cave, and the spring water flowing out is saltpeter water. Saltpeter water is poisonous, and Joe should know that."

This toxic water flows down the hillside into the ponds below. Over the years, the toxicity accumulates in the ponds, eventually causing harm to the human body.

Currently, the villagers' drinking water comes from a pond near the village. The toxicity of the saltpeter in the water is not enough to poison adults, but it is a different story for infants and young children.

Qiao Lizheng also said that when the children in the village fell ill, they had difficulty breathing and their skin turned purple. These symptoms are those of saltpeter poisoning.

As time goes on, the toxicity of the pond will increase. When the toxicity reaches a certain level, everyone in your village will be in danger, and then it will be too late.