Sulfur hexafluoride (SF₆) is a colorless, odorless and fireproof greenhouse gas. Since it is about 5 times heavier than air, it collapses into the glass box and acts as if it were liquid.

Sulfur hexafluoride (SF₆) is a colorless, odorless and fireproof greenhouse gas. Since it is about 5 times heavier than air, it collapses into the glass box and acts as if it were liquid.