Sigma-Aldrich Corporation announced that the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act (HSR Act) in connection with the acquisition expired on Dec. 22, 2014, thereby completing the U.S. HSR Act antitrust notification and review requirement for the acquisition of the Company by Merck KGaA, Darmstadt, Germany.   U.S. antitrust clearance satisfies another condition to closing the transaction, which remains subject to certain other conditions, including regulatory appro...