11.   At least one preliminary test that revealed the presence of anthrax in a Senate mail room.

12.   At least two, the Tennessee Valley Authority and Georgia Power, are under consideration as sites for preliminary tests of tritium-breeding devices.

13.   Because it was a preliminary test, researchers wanted to find out if it was safe.

14.   A hazardous-materials team from Chelsea said preliminary tests for anthrax were negative, said Robert Cannon, a Boston-area Postal Service spokesman.

15.   A law enforcement official said Tuesday evening that preliminary tests for anthrax were negative.

16.   A letter addressed to Daschle contained a suspicious-looking powder that preliminary tests showed contained anthrax, police said on Monday.

17.   A preliminary test did not rule out the possibility the substance was anthrax but more sophisticated tests were needed to confirm the identity, FBI officials said.

18.   A preliminary test indicated the presence of anthrax in the Leahy letter, and the sample now is being tested in an Army lab at Fort Detrick, Md.

19.   A spokesman for the FBI in Louisville said preliminary tests showed the substance in the letter received there was probably not anthrax.

20.   But because the preliminary test is so imprecise, a complete sequencing must be done when it fails to find a possible area of mutation.