Are these chemicals ok to use? Is the weight difference going to be enough to matter.
Depends on the chemicals and the exact state they're in. But I've 'inherited' chemicals from my dad which must be at least 35 years old (and probably closer to 45) that were partly stored not so well. Bottles of what must have been sulfite or metabisulfite had absorbed so much moister through their defective corks that they effectively turned into clumps in a water bath. However, there was also:
* A small bottle of hydroquinone - still works like new. Not clumped.
* A bottle of potassium ferricyanide. Clumped pretty badly, but broken up with a small stick, it works like new.
* Some copper sulfate. Same story; clumped, but in perfect condition.
* Potassium bichromate. Obviously also in like-new condition.
Your silver nitrate is likely still perfectly fine.
In general, observe the following:
* Developing agents (hydroquinone, metol etc.) are good unless badly oxidized.
* Most salts are pretty stable unless (badly) deliquesced. E.g. copper sulfate, bichromates etc. as mentioned above last well. Potassium bromide tends to absorb moisture and clump together, and eventually may deliquesce.
* Activators like sodium/potassium carbonate generally last fine (same as 'salts' above).
* Thiosulfates may deteriorate, particularly ammonium thiosulfate. A heavy sulfur odor is bad news; a mild sulfur odor is normal.
* Compounded developers (i.e. powders that are ready to mix with water) may or may not still work. Depends greatly on how they are stored. Check if they are still dry and light/tan colored.
* Fixer and developer concentrates (liquids) turn bad after X years, with X being small for developers (they tend to last maybe a few years max), and somewhat larger for fixer (unopened bottles of fixer concentrate may be fine for a decade). Fixer concentrates: check for sulfuring out; sulfur tends to precipitate out an attach itself to the walls of the container. Developer concentrates oxidize; check color.
* Acids like acetic acid, sulfuric acid (any concentration) or citric acid, tartaric acid (in powder form) generally last indefinitely. Solutions of citric acid will grow bacterial slime.
* Solutions of sulfite or (meta)bisulfite generally deteriorate rapidly. Discard if they're over a few months old (the smell upon opening the bottle will tell a story...)
