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Define Volatile

October 13, 2014 | A version of this story appeared in Volume 92, Issue 41

Thanks for Glenn Hess’s article “U.S. Seeks Tighter Rail Safety Rules” (C&EN, Aug. 18, page 22). However, the word “volatile” is misused when he writes that “ethanol is less volatile than crude oil.”

“The Associated Press Stylebook and Libel Manual” gives the following guidance: “volatile Something that evaporates rapidly. It may or may not be explosive.”

A Newscripts item from back in the 1970s reported that emergency personnel evacuated an area after the spill of “highly volatile” liquid nitrogen. The public believes the word means explosive, and media, too, often misuse the term.

In what sense is ethanol less volatile than crude oil? Most of us would measure volatility by weight loss in an oven for an hour at say 120 °C. By this test, ethanol is more volatile than crude oil.

Experts say the headspace in a tank of a volatile like gasoline is not explosive because vapor pressure pushes the composition above the upper explosive limit. Less volatile materials, such as diesel fuel, can be within the explosive range. In that sense, ethanol might be less volatile, but that implies that Hess meant explosive rather than volatile. Or is the statement based on flash point?

Interestingly, the word volatile is used correctly on page 23 of the same issue in describing hexanoic acid.

Paul E. Eckler
Wildwood, Mo.


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