Filter petroleum ether and isopropyl alcohol are used to clean residual fuel between testing to make certain there is no cross contamination. A gallon of fuel is only measured as a true gallon when it is at 60 degrees Fahrenheit, so the Langley Air Force Base fuels laboratory must be kept at this temperature to make certain that all tests are accurate. (U.S. Air Force photo by Senior Airman Brittany Paerschke-O’Brien/Released)