By chhun sun chhun.sun@gazette.com -A broken joint bar in the tracks is the cause of a seven-car train derailment last week that spilled a white chemical within yards of homes and near the Martin Drake Power Plant in downtown Colorado Springs, authorities said according to Gazette news partner KKTV. The joint bar connects sections of the rail together. Railway crews spent the past week cleaning up ammonium sulfate, an innocuous substance used in fertilizer that spilled from seven BNSF Railway cars. A spokesperson with the Federal Railroad Administration, which was not involved in the investigation but had officials at the site of the crash, said BNSF officials determined the cause but the railway company's spokesperson did not return messages Tuesday