warming powdered chemicals to drive out moisture

[GoodOldNorm]

Been sorting through my stock of powdered chemicals and found most of them have gone lumpy or solid. I intend to bag them up in double freezer bags. Would it harm the chemicals to slowly dry them out in an oven on a low heat? Would sealing the chemicals in a bag with silica gel be a better method or would it be easier when weighing to allow a bit extra weight for the moisture content and grind the chemicals with a pestle and mortar? Most of the chemicals are sodium salts metol, hydroquinone etc.

[MikeHeller]

I wouldn't apply too much heat especially to chemicals with organic chemicals (developers) in them as this would accelerate any deterioration that may in any case have already happened, or change hydrated chemicals to the anhydrous form changing how they behave and are used when making up the photographic brew. I think I would chuck them.
Mike

[Svend]

Norm, I had this same question a few months ago re. some potassium bromide which I received from the seller in a hard lumpy state. Turns out this was quite OK and the stuff is stable and perfectly usable. In your situation you may want to decide what to chuck and what to keep on a case-by-case basis. Some chems may be stable and fine, and you can simply do as you suggest and just break up the lumps. Others may have deteriorated from the moisture and oxygen -- metol, for example, will likely be a goner if it's turned brown (normal colour being light tan). And, as Mike says, some chems are hydrated and may turn to an unwanted anhydrous form if you dry them. Conversely, I'm pretty sure that if you dried out what was originally photo grade sodium carbonate, you would return it to it's original form by driving off the moisture -- some people do this to hardware store carbonate to get a cheap form of anhydrous photo grade stuff.

There are some members here who have a lot of knowledge of photo chemistry and can advise you better, but I hope this helps a bit.

Best,
Svend

[Martin Aislabie]

Long and low is probably your best bet to dry them - try 12 hrs at 50 ~ 75C.

Break the stuff up as much as possible to help let the moisture out.

Martin