Generally speaking, the poison test often seen in TV series is to use silver to prevent poison, that is, silver (silver needle or silver hairpin) will turn from silver to black when it encounters poison, so as to judge whether food is poisonous or not. However, from the perspective of modern biochemistry, some highly toxic substances that most people are familiar with are arsenic, cyanide, pesticides, snake venom and so on. Most of them do not react directly with silver. Naturally, there is no silver.

But arsenic can: the poison mentioned by the ancients mainly refers to highly toxic arsenic, namely arsenic trioxide. Interestingly, no matter from the chemical reaction theory or from the specific chemical experiments, silver with fairly stable metal properties will not react with arsenic under general conditions, that is, there is no phenomenon that silver will turn black when it meets highly toxic arsenic, as the ancients said. In fact, arsenic is oxidized by arsenic, which is extracted from various arsenic-containing minerals, among which arsenopyrite is the main ore (containing about 46% arsenic). However, it often coexists with many other sulfides and sulfides, and may be accompanied by natural sulfur, which may discolor silver. Because the ancient people's technology of making arsenic is very poor, the arsenic used by the ancients may be accompanied by a small amount of sulfide and sulfur. When it meets silver, it will naturally change the color of silver.