NEW YORK — Tests on an artillery shell that blew up in Iraq on Saturday confirm that it did contain an estimated three or four liters of the deadly nerve agent sarin (search), Defense Department officials told Fox News Tuesday.

The artillery shell was being used as an improvised roadside bomb, the U.S. military said Monday. The 155-mm shell exploded before it could be rendered inoperable, and two U.S. soldiers were treated for minor exposure to the nerve agent.

Three liters is about three-quarters of a gallon; four liters is a little more than a gallon.

"A little drop on your skin will kill you" in the binary form, said Ret. Air Force Col. Randall Larsen, founder of Homeland Security Associates. "So for those in immediate proximity, three liters is a lot," but he added that from a military standpoint, a barrage of shells with that much sarin in them would more likely be used as a weapon than one single shell.

The soldiers displayed "classic" symptoms of sarin exposure, most notably dilated pupils and nausea, officials said. The symptoms ran their course fairly quickly, however, and as of Tuesday the two had returned to duty.

The munition found was a binary chemical shell, meaning it featured two chambers, each containing separate chemical compounds. Upon impact with the ground after the shell is fired, the barrier between the chambers is broken, the chemicals mix and sarin is created and dispersed.

Intelligence officials stressed that the compounds did not mix effectively on Saturday. Due to the detonation, burn-off and resulting spillage, it was not clear exactly how much harmful material was inside the shell.

A 155-mm shell can hold two to five liters of sarin; three to four liters is likely the right number, intelligence officials said.

Another shell filled with mustard gas (search), possibly also part of an improvised explosive device (IED) was discovered on May 2, Defense Dept. officials said.

The second shell was found by passing soldiers in a median on a thoroughfare west of Baghdad. It probably was simply left there by someone, officials said, and it was unclear whether it was meant to be used as a bomb.