The blackening agent for tin contains ammonium hydrogen fluoride and is stable without peculiar smell ; it is totally suitable for automatic production with no need of ventilation .

由此 锡发黑剂配制的 锡发黑液含有 氟化氢铵，稳定，没有异味，不用抽风装置，完全可以自动化生产。

Thus the tin was released from the plating bath using 2.5 g ammonium fluoride as the releasing agent in a acetic-pyridine buffer solution of a pH value 5.5 and then inversely titrated using zinc nitrate standard solution in the presence of xylenol orange as an indicator .

在pH值为5.5的醋酸吡啶缓冲溶液中，用 2.5gNH4F解蔽，4滴XO、1mLCPB指示终点，锌盐返滴定镀液中的 锡。