Simplify the following text for a Grade 13 native English-speaking person.
Original: Mercury ( II ) chloride ( also known as mercuric chloride or corrosive sublimate ) was once used to treat syphilis ( along with other mercury compounds ) , although it is so toxic that sometimes the symptoms of its toxicity were confused with those of the syphilis it was believed to treat .
Simplified: Together with other mercury compounds , Mercury ( II ) chloride ( also known as mercuric chloride or corrosive sublimate ) was used to treat syphilis .