<p>The fourth application of Calcium Carbonate is explained later in the manga/anime and it's a bit of a spoiler.
But it's used in :</p>

<blockquote class="spoiler">
  <p> The making of Gunpowder. It's explained in Chapter 7 The gunpowder adventure and the third episode of the anime Weapon of science.</p>
</blockquote>

CC BY-SA 4.0
2019-08-13T15:55:09.193Z
And yet, that doesn't make sense.  You make gunpowder from potassium nitrate.  They extract potassium carbonate (I think) from seaweed not shells.  And ideally you would actually make KOH from ash and then use that to neutrallize nitric acid to make KNO3. CaCO3 should have be relevant to gunpowder unless I'm missing something.
kaine
CC BY-SA 4.0
2019-08-13T16:00:46.627Z
(also it would be easier to just use guano from the cave)
kaine
CC BY-SA 4.0
2019-08-13T09:10:08.730Z
2019-08-13T09:10:08.730Z
HolyHugo
<p>From what the first three stated and from a little research, I think it may be the combination of the three which is HUMAN CIVILIZATION. Because,
from what i have read in on <a href="https://www.ima-na.org/page/what_is_calcium_carb" rel="nofollow noreferrer">this page</a> and from analysis, it is a very essential compound for the start of a human civilization.</p>

<p>And according to that link, “chalk” is composed of calcium carbonate and used in writing 10,000 years ago. Well, writing IS a form of communication and thus increases the chances of survival and thus “realize it is major spoilers” and thus, evolution of stone age to modern age. That is what i had in mind. </p>

CC BY-SA 4.0
2019-08-13T08:38:26.183Z
2019-08-13T17:47:53.770Z
2019-08-13T17:47:53.770Z
Loli_No Brainer
<p>In the second episode of the anime, Senku Ishigame said the Calcium Carbonate they were gathering had four applications. Fertilizer for growing crops, raw material for building houses and soap. </p>

<p>What's the fourth application of Calcium Carbonate according to Senku ishigame?</p>

CC BY-SA 4.0
2019-08-13T16:12:05.377Z
(Side thing but CaCO3 is not fertilizer at all.  It neutralizes acidic soil without making it basic. If you inspect a maple tree, (for an easily observable example), the leaves will make the soil around it very acidic making it hard for things to grow there.  That happens with farming over time.  Adding CaCO3 rectifies this.)
kaine
<dr.stone>
What's the fourth application of Calcium Carbonate according to Senku ishigame?
# What's the fourth application of Calcium Carbonate according to Senku ishigame?
Posted by: username_0 on 2019-07-19
In the second episode of the anime, Senku Ishigame said the Calcium Carbonate they were gathering had four applications. Fertilizer for growing crops, raw material for building houses and soap.

What's the fourth application of Calcium Carbonate according to Senku ishigame?
**Tags:** dr.stone
> **Comments:**
> **username_1**: (Side thing but CaCO3 is not fertilizer at all.  It neutralizes acidic soil without making it basic. If you inspect a maple tree, (for an easily observable example), the leaves will make the soil around it very acidic making it hard for things to grow there.  That happens with farming over time.  Adding CaCO3 rectifies this.)  
---
## 2 answers
### Answer by username_2 on 2019-08-13. Score: 2 | Accepted answer
The fourth application of Calcium Carbonate is explained later in the manga/anime and it's a bit of a spoiler.
But it's used in :

> The making of Gunpowder. It's explained in Chapter 7 The gunpowder adventure and the third episode of the anime Weapon of science.
> **Comments:**
> **username_1** (2019-08-13): And yet, that doesn't make sense.  You make gunpowder from potassium nitrate.  They extract potassium carbonate (I think) from seaweed not shells.  And ideally you would actually make KOH from ash and then use that to neutrallize nitric acid to make KNO3. CaCO3 should have be relevant to gunpowder unless I'm missing something.  
> **username_1** (2019-08-13): (also it would be easier to just use guano from the cave)  
---
### Answer by username_3 on 2019-08-13. Score: 0
From what the first three stated and from a little research, I think it may be the combination of the three which is HUMAN CIVILIZATION. Because,
from what i have read in on [this page](https://www.ima-na.org/page/what_is_calcium_carb) and from analysis, it is a very essential compound for the start of a human civilization.

And according to that link, “chalk” is composed of calcium carbonate and used in writing 10,000 years ago. Well, writing IS a form of communication and thus increases the chances of survival and thus “realize it is major spoilers” and thus, evolution of stone age to modern age. That is what i had in mind.
---
