1. Bittern bittern is also called bittern and bittern alkali. It is the mother liquor left in the salt pond after salt is made from seawater or salt lake water. The main components are magnesium chloride, calcium sulfate, calcium chloride and sodium chloride, which are bitter and toxic. After evaporation and cooling, magnesium chloride crystals are precipitated, which are called halogen blocks.

Nitrite, a kind of inorganic compounds. Mainly refers to sodium nitrite, which is white to light yellow powder or granular, slightly salty and easily soluble in water. The appearance and taste are similar to salt, and it is widely used in industry and construction, and it is also allowed to be used as a chromogenic agent in meat products in limited quantities. The probability of food poisoning caused by nitrite is high. Eating 0.3 ~ 0.5g of nitrite can cause poisoning and even death.