How much do you reuse your Schiff's, and that test is invaluable.

Also, Culling taught me to make up the periodic acid fresh, daily!
It is not stable forever.  We also use a coplin jar of Schiffs for a 
week, then dipsose of it properly, and we never put working Schiffs
back into the stock bottle (have seen that done!)  If the Schiffs is
turning pink before use, it may also be bad, and do not freeze it.

Culling also taught us to just wash with running tap instead of sulfurous
acid rinses, works just fine.

Gayle Callis