Why did silver needles have to be used in drug testing in ancient times?

Because silver objects such as silver needles will turn black immediately after encountering something, mainly due to the interaction between silver and sulfide.

The method of testing poison with silver needle or silver hairpin has been around 1000 years, so it is an old method and an old legend. According to the analysis of modern medical theory, although this method is not completely scientific, it can be asserted that it has great limitations. ? ?

Sulfide can form dark silver sulfide on the surface of silverware, making silver needles look black. This has nothing to do with the role of "toxin". Therefore, as long as you encounter a substance containing a lot of sulfur, whether it is toxic or not, the silver needle will turn black after insertion.

On the contrary, some highly toxic substances, such as arsenic, potassium cyanide and sodium cyanide, etc. They don't turn black when tested with silver needles because they don't contain sulfur.

The poison mentioned by the ancients mainly refers to the highly toxic arsenic, namely arsenic trioxide. The backward production technology in ancient times led to a small amount of sulfur and sulfide in arsenic. The sulfur contained in it can react chemically with silver, so that a layer of black "silver sulfide" is formed on the surface of the silver needle.

In modern times, the technology of producing arsenic is much more advanced than in ancient times, and it is refined very pure, and there is no sulfur or sulfide. Silver metal is chemically stable and will not react with arsenic under normal circumstances. It can be seen that the ancients used silverware to test drugs because of historical and scientific limitations.

Some things are not poisonous, but they contain a lot of sulfur, such as egg yolk, which will turn black when silver needles are inserted. On the contrary, some are highly toxic substances, but they do not contain sulfur, such as toadstools, nitrite, pesticides, rat poison, cyanide and so on. When silver needles touch them, there will be no black reaction.

Therefore, the silver needle can not identify poisons, nor can it be used as a tool to detect poisons. Although silver can't detect poison, it can be disinfected. As long as every liter of water contains one milligram of 50 million silver ions, most bacteria in the water can be killed.

Its principle is that silver can form positively charged ions in water, adsorb bacteria in water and gradually enter bacteria, so that its catalyst-anchoring system is deactivated, and bacteria lose their metabolic ability and die. Therefore, it is good to use silver to make dishes and chopsticks in daily life.

To sum up, it is precisely because of the reaction between silver needles and highly toxic drugs that ancient people used silver needles to try drugs.