... THE EXPLOSION OF A SPANISH STEAMER Madbid, August 20, — Particulars have bee t received here of the losa of the Spanish merohan Eipress, at Barcelona, by tbe explosion of a quantity of powder and cartridge wbich sbe was loading, intended for the Royal army besieging the citadel of Sco de Urgel. The catastrophe occurred at five o'clock ou the evening of the 17th inst.. in the port of Barcelona. ...