John,
You will know my relationship with Charlie Culling and I did have the 
very great pleasure of meeting him - at a Biological Stains 
Commission meeting.  He was wonderfully friendly and a great 
companion at dinner.  It is of him that it was said "He never knew an 
enemy" - to meet him was to like him.  Did you know he stood as a 
Parliamentary MP once? (for USA citizens, that's Member of 
Parliament, not Military Police!)

However, unscientific, improper and illogical though it is, I can 
confirm the stability of 1% periodic acid at room temperature.  Even 
further, if kept in a glass topped Coplin jar, on the bench, provided 
you do not have equatorial temperatures, it can be used and re-used.  
This applies to 1, 2, 3 or four slides at a time.

It is important, not just for these debatable pracitices, that slides 
be washed in distilled water, before periodic acid treatment.

It is also important to be aware of the reason the PAS is being done. 
 For strict histochemical uses, I would always use fresh periodic 
acid.  If confirming mucin secreting cells in a pleomorphic adenoma, 
for example, I do not believe the storage of the periodic acid is 
anywhere near so critical (ALWAYS use appropriate controls you are 
familiar with).

Our periodic acid sits in the Coplin jar, on the "staining bench" for 
weeks (as many as 4-6)  and regularly accomodates new slides and 
treats them as if it were virginal.  There is an awful lot of 
tolerance in the PAS providing you are not using it for direct 
comparative purposes, or seeking the tiniest deposits for typing some 
particulary difficult tumour.  (if BC is reading, he will probably 
let us know of fine pigment deposits to which this also applies.)

Goes against everything I have been taught - by Charles amongst 
others - except that it works for most purposes!

There is some 10-15 years experience in these sentiments and the same 
time of participation in a Welsh National External Quality Assurance 
Scheme for Technical Histology (more latterly, a UK wide one) with 
ALWAYS good scores for our PAS on whatever material is thrown at us.

Jeepers, that's a bit of a monologue!  guess it's what comes from 
being quiet so long (Easter and all that)
Russ Allison, Wales