SECOND US POISON SCARE A second suspected case of the deadly poison ricin is being investigated in the United States. An envelope containing a suspicious powder, addressed to the Republican National Committee and found in a Connecticut post office, is being tested. The letter was discovered hours after a powder which initially tested positive for ricin was found in a US Senate mailroom. Officials in Connecticut said field tests of the powder were inconclusive but all mail associated with the envelope was isolated until laboratory tests were completed. "We are performing a battery of tests for biological and chemical agents,...