# Heat sealed glass jar with water- will it break?

1. Nov 26, 2015

### megawatt

If you fill a glass jar with water, or any other liquid, then seal the jar tightly , then heat the jar, will the jar break as the liquid inside tries to boil? Is it a dangerous experiment to try?

2. Nov 26, 2015

### Dr. Courtney

Depending on how much heat, it can be dangerous, as the pressures can become very large and burst the jar.

3. Nov 29, 2015

### megawatt

What about the boiling point of the liquid inside the jar? Suppose the jar is full of water, and you heat it to 101 degrees C. Will the pressure be so great at that point? What about when you are canning food. Don't you cover the jars and place them in boiling water for several minutes to sterilize the contents? So I figure at this point the pressure must not be high enough to burst the jars?
How high can you safely heat the jars while canning?

4. Nov 29, 2015

### CWatters

You don't do the lids up tight when making jam or they can explode. A tin can isn't so rigid.

Increasing pressure increases the boiling point,

5. Nov 30, 2015

### jbriggs444

During canning, water evaporates into the head space in the jars. As the temperature of the jars approaches boiling, the partial pressure of water vapor in the head space approaches one atmosphere. Together with the preexisting air, this could lead to a total pressure as high as of two atmospheres in the head space. Because the lids are not sealed tightly, some gas mixture escapes. Part of this mixture will be water vapor. Part will be air. The result is that the partial pressure of air in the head space is reduced.

When heat is removed, the water vapor condenses. The total pressure in the head space decreases and the lid is pulled inward, making the seal tight. If the heat was enough to sterilize the contents and if the vacuum seal forms then the canned food will not be subject to bacterial decay. One insures the former by boiling the jars long enough. One insures the latter by "pinging" the jars to make sure that the lids are on tight.

When I have done home canning, we always used a water bath. This means that the temperature of the jars never exceeds boiling.