Upon hearing this, Qiao Lizheng was immediately shocked.

Zhao Xian's words were hard for him to believe. The villagers all grew up drinking pond water, and he simply couldn't believe that the water was poisonous.

Seeing this, Zhao Xian continued, "The water in the pond is less toxic, but that doesn't mean it's not poisonous. This stream flows down the mountain and all of it flows into the pond below."

The village has many ponds that are interconnected, which means that all the water sources in the village, large and small, contain toxins.

I have a way to test the toxicity of nitrate solution.

Jolie could take the stream water flowing from the cave back to give to the newborn kittens and puppies. They should die from poisoning soon; you can tell by looking at their symptoms.

This method, though somewhat cruel, is very effective. To uncover the truth behind the deaths of the children in the village, this method is worth a try.

Qiao Lizheng remained silent for a long time before finally speaking:

"Since that's the case, I'll take some stream water back with me. Even if I believe the water is poisonous, the villagers won't believe me. I need to find a way to let the villagers know the truth."

If the village's water source becomes poisoned, Fudu Village will become uninhabitable, and everyone will have to leave and find a new place to live.

Because Qiao Li was eager to know the truth, he found an earthenware pot, filled it with stream water, and hurriedly went down the mountain.

After Qiao Lizheng left, Zhao Xian and the others prepared to enter the cave to see what was inside.

The cave was completely dark, so preparations had to be made before venturing inside.

The soldiers made several torches, and they also brought weapons to guard against wild animals in the cave.

Li Xue also wanted to go into the cave to take a look, but Zhao Xian disagreed, saying that the cave was extremely dark and damp, and that she would definitely be soaked when she came out.

That really worked. As soon as Li Xue heard it, she gave up her plan to go into the cave. It would definitely be uncomfortable for a girl to come out of a cave all wet.

With everything prepared, Zhao Xian and Li Guang led more than ten soldiers, lit torches, and entered the cave.

The entrance to the cave is not large, just enough for one person to pass through, but after walking a few dozen steps inside, the space begins to expand.

Since we had just entered, our eyes were not yet used to it and we couldn't see anything clearly. After we got used to the surrounding environment, we gradually saw the situation inside the cave under the light of a few torches.

At this moment, everyone smelled a faint sulfurous odor. It is perfectly normal to smell sulfur in a saltpeter mine, so it can now be confirmed that this is indeed a saltpeter mine.

The air inside the cave was very humid, giving a sense of oppression and a mysterious atmosphere.

The deeper you go into the cave, the more spacious it feels. Under the torchlight, you can clearly see that the cave walls are covered with dense mineral veins.

Some of these veins resemble winding rivers, some look like giant dragons, and some even resemble castles from fairy tales.

Mineral veins are masterpieces of nature's artistry; they may appear chaotic, but there are patterns to be found.

Zhao Xian didn't know much about geology, but he could still tell that it was a nitrate vein.

These mineral veins have retained their original form despite millions of years of rain erosion, making them a precious resource and a gift from nature.

In ancient times, saltpeter was mainly used to make gunpowder and fireworks, and it could also be used in medicine.

Moreover, saltpeter can improve soil and promote crop growth, making it an excellent fertilizer that can significantly increase crop yields.

Seeing the scene inside the cave, Zhao Xian and Li Guang were overjoyed. Judging from the trend of the vein, this was a huge nitrate deposit with immeasurable value.

Deep inside the cave, the space was enormous, and the ground was covered with fallen ore. Judging from the situation, it would be very convenient to mine the saltpeter here.

By this time, the torches they had brought in were almost all used up, and if they didn't get out soon, they wouldn't be able to see anything at all.

Zhao Xian ordered his soldiers to bring some ore out of the cave.

Li Xue waited outside for a long time and began to get anxious. She only felt relieved when everyone came out of the cave.

It was so dark inside the cave that it took a long time for everyone's eyes to adjust.

The cave was too humid, and their clothes got soaked. Fortunately, Li Xue lit several campfires outside, and the group went to the fires to warm themselves.

The saltpeter brought out was put together in a small pile. These ores were grayish-white crystals that sparkled in the sunlight.

"I know that pharmacies sell saltpeter as medicine at very high prices. Now that we've discovered a saltpeter mine here, it's hard not to get rich."

"What should we do with this nitrate ore? Should we mine it?" Li Xue asked.

Upon hearing this, Zhao Xian couldn't help but laugh.

"It is definitely not allowed to mine minerals privately. According to the regulations of the imperial court, all mineral resources belong to the state, and this nitrate mine shall naturally be mined by the imperial court."

We can purchase saltpeter and produce related products for sale.

"I know that saltpeter can be used in medicine and to produce gunpowder and fireworks. Besides that, what else can saltpeter be used for?" Li Xue asked.

"Food is the most important thing for the people. Every dynasty has paid attention to grain production. In order to produce more grain, in addition to reclaiming wasteland, we can also increase the yield of crops."

To increase crop yields, fertilizers must be used, and the practice of making fertilizers from saltpeter has existed since ancient times.

If we can use saltpeter to produce fertilizer for crops and increase yields, it would be equivalent to opening up a large amount of wasteland.

Therefore, when we return, we should bring back plenty of saltpeter to manufacture fertilizer. We can conduct trials first, and once the results are significant, we can promote the use of this fertilizer.

As they were chatting, Qiao Li rushed over. Upon seeing Zhao Xian, he quickly said:

"Lord Zhengyang is right, this water is poisonous. I just went back to the village and found a newborn puppy, and gave it some stream water that I brought from the mountain to drink."

Soon after, the puppy began to have difficulty breathing and started convulsing. It died shortly afterward.

When the puppy died, its eyes turned blue; it was in great pain.

The villagers now know what happened; they know the water is poisonous, and now they dare not even drink it.

"With so many people in the village, we can't go without water. Please, Marquis Zhengyang, help us find a solution."

Zhao Xian nodded. It was a good thing that the villagers knew the truth, so he wouldn't have to waste his breath explaining. With that in mind, he spoke up.

"Qiao Lizheng, there's no need to worry. I've noticed that there's a flowing river about two miles from Fudu Village. The water there is safe to drink."

Of course, the water in the pond is also a good thing. Although it is poisonous, it is an excellent fertilizer. Using such water to irrigate crops will greatly increase the yield.

This is a treasure for your village; you must make good use of this water and not waste it.