A third baby has died in connection with China's spreading scandal over tainted milk formula and more than 6,200 infants have become sick, Health Minister Chen Zhu said Wednesday.  China's quality watchdog says that its inspectors have found melamine in milk powder made by more than 20 Chinese companies.  The widening scandal is an embarrassing failure for China's product safety system, which was overhauled to restore consumer confidence and preserve export markets after a string of recalls and warnings abroad over tainted toothpaste, faulty tires and other goods.  Chen told a news conference that of the 6,244 babies that have fallen ill, 158 were suffering from acute kidney failure.