Historical clue formulations

• I- — 2023-05-28
• I-, in chemistry — 2019-03-06
• Silver ___ (cloud seed) — 2004-09-28
• NaI, e.g. — 2000-06-07
• NaI, e.g., chemically — 1998-07-13
• Chemical salt — 1998-04-16
• Silver _____ (cloud seed) — 1994-07-22