<http://www.ukaps.org/forum/viewtopic.php?f=11&t=20883>Potassium decays with a half-life of 1250 million years, meaning that half of the K atoms are gone after that span of time, so don't store your solution longer than 1250,000,000 years or you will have to use them at double strength.
Corrected....ceg4048 said:That's not the same as going off.
A lot of salts are "hygroscopic" <http://en.wikipedia.org/wiki/Hygroscopy> and form hydrates, but this really is just added water as Clive says. You can think of salt (NaCl) as an example, where in a dry climate you can naturally go from salt lake to salt pan to salt lake to salt pan etc. as the water content rises and falls.Actually they change into a less usable form, as some of the EI salts absorb atmospheric water and turn to one solid lump.