Kevin McCue wrote:

Easy to check for alcohol in fuel. Put a small quantity of water in a
jar. add some "suspect" fuel. Cap and shake. Let settle. If water has
disappeared alcohol is likely.

The water will not disappear. Put the water in and mark the level. Then add
the fuel and shake. Let the water settle back out. If the water level is now
higher, there's alcohol in the gas.

George Patterson
Brute force has an elegance all its own.