| Answer | Crossword Clue |
|---|---|
| SINKTOTHEBOTTOM | Prove not to be buoyant |
| BURN | Prove not to be fireproof |
| rule | to prove to be unrelated or not for consideration; eliminate; exclude |
| SINK | Prove not buoyant |
| unchallenged | Not called on to prove one's identity or allegiance |
| SINKTOTHEBOTTOM | Fail to be buoyant |
| ballonets | The compartment in a balloon or airship into which air or another gas can be forced in order to maintain the craft's shape as buoyant gas is released |
