Historical clue formulations

• Fertiliser ingredient — 2014-11-21
• Saltpetre — 2014-10-14
• KNO3, in Britain — 2013-03-24
• Saltpetre — 2004-10-15
• Saltpeter, to a Brit — 2003-12-07
• Saltpetre — 1999-07-06
• Saltpeter: Brit. — 1998-07-13
• British fertilizer — 1997-02-03
• Saltpeter, in Salisbury — 1996-04-09
• Potassium salt — 1994-05-24
• KN03 — 1994-04-21