July 13, 1837 the sidewheel steamer Union suffered a boiler explosion. The Union operated between Alexandria, Virginia and Prince George's County, Maryland. At around 3 P.M. the boiler exploded sending bolts, fragments of steel and other debris into the passengers. Three were killed, this included the wife of the engineer. The explosion was caused when material that was used to plug a leak in the boiler fouled the tubes. The material used...horse dung.