The fluoric acid, disengaged in the gaseous state, combines with the water that diluted the sulphuric acid, and forms liquid fluoric acid, by which the glass is corroded.

The fluoric acid, disengaged in the gaseous state, combines with the water that diluted the sulphuric acid, and forms liquid fluoric acid, by which the glass is corroded.

It contains fluoric acid, which may be the means of this change.