[kevinnn]

   I was just wondering, I had a sample of KNO3 that I heated to get rid of some of the water within the sample.  My question is, is there anything I could do to know if it is starting to decompose, and not giving off water vapor?  Also was this a good compound to do this with, because there was what appeared to be a lot of steam.  Thanks to all feed back. 

[batsonb]

As I recall, potassium nitrate has a fairly low melting point for an ionic crystal.  It would be a poor choice to determine water content.  It has very little water, usually.  It melts and thus would be completely anhydrous at that point. Stop heating at that point.

[bidiboom]

   I was just wondering, I had a sample of KNO3 that I heated to get rid of some of the water within the sample.  My question is, is there anything I could do to know if it is starting to decompose, and not giving off water vapor?  Also was this a good compound to do this with, because there was what appeared to be a lot of steam.  Thanks to all feed back. 

To my knowledge, all of the ionic compounds of NO₃ are soluble.. by heating aq. sol. of it, you lose all of the water and there you are left back again with KNO3, only with a structural change.. if you can heat it to a pretty high level, then you can make it happen a chem.reaction (See "Properties" part):
http://encyclopedia.thefreedictionary.com/Potassium+nitrate    

[MsRhode312]

by heating any matter it changes the phase of matter.