How was gunpowder used to extablish proof of alcohol?

Here's why:

* Proof of alcohol refers to the percentage of alcohol by volume in a beverage. This is typically determined using hydrometers or other analytical methods.

* Gunpowder is a explosive mixture containing sulfur, charcoal, and potassium nitrate. It is not related to alcohol in any way.

It's possible you might be thinking of a different method for testing alcohol content, or there might be a misunderstanding.

Could you clarify your question? Perhaps you were thinking of a different method for testing alcohol content, or are you referencing a historical anecdote you've heard?