Rockford fire officials responded to a hazardous material spill Wednesday afternoon.
A passerby noticed a mysterious liquid pouring from a train car at a lot near Winnebago and Cedar Streets.
Fire officials say the substance is argon, a liquid gas used for refrigeration. The cause of the spill is not known, but the aging rail car holding the gas could be a factor.
The substance is dangerous but fire officials believe the situation is under control. The spill is contained and in an open area.
The railcar is owned by air liquid, based in Burlington, Wisconsin. Company officials have been notified.