The influence of chromium on the bismuth-system superconductors (Bi-SC) was found as a by-product in a crystal synthesis experiment using a high-temperature-pressure-vessel (HTPV). The main product in the HTPV was found to be a 2201 phase of the Bi-SC, while the product in air from the same raw materials was a 2212 phase. This difference is attributed to an impurity from the HTPV. It was found from other experiments that chromium stabilizes the 2201 phase of the Bi-SC and chromium decreases the 2212 phase.