1) Buy a 10 ml graduated cylinder
2) Mark an extra 11 ml line above the 10 ml level
3) Add 10 ml of the gas you want to test
4) Add 1 ml of water up to the new 11 ml line
5) Put your thumb over the top and shake the sh*t out of it
6) Set it somewhere and let it settle
7) If you now see 1.5 ml of separated liquid at the bottom...you have approx 5% gasahol.
note...some of the separated liquid will stick to the sides of the cylinder...and I'm not totally sure the 1 ml of water is enough to draw out all of the ethanol....or whether it also draws out other elements of the gas.
Graduated cylinder - Wikipedia, the free encyclopedia