All of these chemicals are useful and stump removers can be an easy to obtain source for them. The stump remover SHOULD be labeled. But if it isn't you can perform these tests.
First mix an equal portion of sugar and stump remover and add sulfuric acid. This might cause the mixture to catch fire (add more acid if it doesn't go at first). If it does, it's most likely potassium or sodium chlorate (usually potassium).
If it doesn't light with sulfuric acid, then try torching it. If it starts to burn on it's own, then it's potassium nitrate.
To be absolutely certain, you can run the nitrate test we already showed in a previous video: http://www.youtube.com/watch?v=f5M3rUqaEYs
If it's sodium metabisulfite, it won't burn with sugar under any circumstances. To confirm it's metabisulfite, in a separate container of 10mL of water add 1gram of the stump remover and 0.5 grams of iodine from one of our previous videos: http://www.youtube.com/watch?v=2F_kPXbi2D8
If it is sodium metabisulfite it will fizz and dissolve as seen in the video.
Once you've identified the stump remover you can start doing experiments!
Chlorate - Make fire without matches: http://www.youtube.com/watch?v=vgh76gPSg3M
Chlorate - fire storm in a test tube: http://www.youtube.com/watch?v=vJbllSaj_L4
Nitrates - Make nitric acid: http://www.youtube.com/watch?v=2yE7v4wkuZU
Metabisulfite - Make Sulfuric Acid: http://www.youtube.com/watch?v=okvvD3-DF9U