A number of substances have been used as positive contrast agents: silver, bismuth, caesium, thorium, tin, zirconium, tantalum, tungsten and lanthanide compounds have been used as contrast agents.
许多物质已被用来作为阳性造影剂：银，铋，铯，钍，锡，锆，钽，钨和稀土化合物已被使用造影剂。
2
The test results show that it is technically feasible to separate silver from crude bismuth by vacuum distillation instead of traditional Parke's process of desilverization(zinc desilverization).
试验结果表明，采用真空蒸馏法脱除粗铋中银代替传统的加锌除银法，在技术上是可行的。
3
Processes for extracting metals from the slurry and recovery rates of them, such as gold, silver, copper, antimony and bismuth, and measures of controlling arsenic pollution are discussed.