I have bought a stump remover for KNO3 and it has the numbers 13-0-44, which i have heard is pretty good. I was just wondering, how pure is it? and also if i could remove those impurities. I have tried making BP with it and it didn't do much. lots of excess sulfur and charcoal was left over, so im thinking that its not so pure. Also, if a product has the same numbers as another one, are they exactly the same purity?