When mental patients are not sick, sulfuric acid is not difficult to get, just like normal people. Daily necessities and chemical stores can be bought. The crime of mental patients is a headache for all countries in the world, and it cannot be effectively prevented. In countries with relatively sound legal system, mental patients will be sentenced to one and a half hospitals and half prisons if they commit violent crimes. On the one hand, they will be controlled, on the other hand, they will be treated. Of course, the cost will be paid by the government. In China, mental patients are innocent of committing crimes. Even if they are sent to a mental hospital, their families have to bear high expenses, and mental patients cannot be effectively controlled.