[reverse flash]

I am doing some research into test reagents like mandelin, marquis I see that some contain some crystals.
Any idea of the purpose or what it might be. They do not seem to be dissolving / reacting with H2SO4, which makes about 95 % of the test reagent.

see picture below

http://i48.tinypic.com/pw13o.jpg

[Arkcon]

There are many possibilities, and you may be able to find them in a reference related to these test reagents.  However, we can work to try to figure the question out.  Can you tell us quickly what the reagents are?  I couldn't but the answer was a quick Wikipedia search away.  Do you know what re3action these reagents are meant to undergo? 

[reverse flash]

For example mandelin test reagent is used to detect many drugs, is presence of aspirin for example it turns green, heroin light brown etc.
There is a lot of info how to make them in wikipidia but I cannot find anything about those mysterious crystals. I suspect it is some kind of preservative or catalyst.

here is sample color chart for them

http://www.neurosoup.com/drug-test-kit-chart/

[Arkcon]

Or they're excess reagent in solution.  These test reagents are use essentially pure sulfuric acid as a solvent.  Even tiny amounts of reagents may not dissolve completely.

[reverse flash]

Mandelin reagent is 95 % sulfuric acid and only a little ammonium metavanadate, you can add more ammonium metavanadate and no cystals.

This is some kind of salt added extra later