I've read that the HT-2 test, a silver for sulfur test, has
a two month life span. My HT-2 came from P. Formulary
and they may have been the source of information.
Silver nitrate and acetic acid make up the HT-2 test. I
don't know why it should go bad; if it does. I've asked the
same question of this group and gotten no response.
Apparently the reactions involved are more complex
then would first seem to be the case. One thing I think
for certain; the sulfide of silver is produced if there be any
sulfur present. From reading of the test, the acid is present
to free sulfur from any remaining thiosulfate. But nitrate
is a very strong oxidizer and so why sulfur rather than
a sulfate being freed? For that matter why a sulfide
of silver and not a sulfate.
At any rate I'm not going to buy any more HT-2 or compound it
until I find out why it should go bad. I think the HT-1a test,
properly done, will do just as well. Dan