Simplify the following text for a Grade 7 native English-speaking person.
Original: Heating of mercury , or compounds of mercury that may decompose when heated , is always carried out with adequate ventilation in order to avoid exposure to mercury vapor . The most toxic forms of mercury are its organic compounds , such as dimethylmercury and methylmercury .
Simplified: Mercury ( I ) chloride is one of the most common mercury ( I ) compounds .