"Ok, so an (Amazon Associate paid link to a) graduate cylinder, and what I assume is fuel. But no details on what test you're doing, how you're doing it, or how to interpret the results. Let me rush right out to click your link, buy the cylinder, and pour some gas into it. Not that I'd know what the hell anything meant, but hey, you'd make a dime, right?"

--- Anonymous

While this comment is a remarkably trollish response to a blog post meant to show you tidbits of our personal life, I had been meaning to give our readers more details on how simple it is to perform a test for ethanol content of gasoline.  All you need is something that easily measures volume --- a 100 mL or larger graduated cylinder takes nearly all the math out of your hands, but you could just as easily use a ruler in a straight-sided glass cup or jar.

The idea is that when you mix water with gas, any ethanol in the gas comes out of solution and joins the water instead.  So all you have to do is know how much water you initially added to the gas, subtract that out of the clear layer at the bottom of your graduated cylinder at the end of the experiment, and the rest of the clear substance is ethanol.

When starting your ethanol test, the first step is to take your gas sample carefully.  As a far-more-constructive commenter mentioned, you should run at least a gallon of gas into your car before taking a sample from any pump that uses a shared hose.  Then pump a sample into a container and bring the gas home to experiment.

In the meantime, you should take a minute to prep your graduated cylinder (assuming you're like us and only bought a 100 mL one instead of a cylinder with a larger capacity).  Later in the experiment, you'll need to know where the 110 mL line is, which is easy to guestimate by measuring the distance between the 90 and 100 mL lines, then measuring that same distance above the 100 mL line.  To keep things simple, use a piece of tape to wrap around the graduated cylinder at the 110 mL line, marking its location.

Now you're ready to add the gas.  I found it much easier to pour some gas into a small container rather than trying to fill the graduated cylinder from the gas can.  You want to add gas up to the 100 mL line, and don't forget your chemistry lessons --- read from the bottom of the meniscus!

Top the gas off with 10 mL of water, meaning that the total liquid level should match the taped 110 mL line.  Then mix the contents.

(Mixing was the hardest part for me because our graduated cylinder didn't come with a stopper, and I ended up slopping a bit of liquid out while plugging the top with my palm.  I think a better solution would have been to use a sandwich baggie pulled over the top of the graduated cylinder, or to invest in some parafilm.  Either way, thorough mixing is imperative.)

After mixing, the clear ethanol and water will settle to the bottom, while the colored gas will sit above it.  You can easily measure how much water and ethanol is present, then subtract 10 mL from that to find the percent ethanol in the water.  Probably because of my sloppy mixing, our clear layer came to 17 mL, producing a reading of 7% ethanol instead of the 10% listed on the pump at the gas station.  (If you didn't use the exact amounts of gas and water I listed above, you'll have to do a bit more math: ((Clear layer - Water)/(Gas))x100%.)

As Mark has mentioned previously, ethanol in gas can wreak havoc on many of the small engines found on our farm, so it's useful to know for sure that the ethanol-free gas we've hunted down really doesn't have any ethanol in it.  We'll be testing gas stations soon and hoping to find one near us that is really ethanol-free.