Hi. Recently, we conducted an experiment where we were supposed to determine the optimal 'water:ammonium nitrate crystal' ratio to keep the water at a minimum temperature for a maximum length of time. What we did was take different samples of ammonium nitrate (1g, 2g, 3g...6g) and dissolve what we could into 5mL of water. We then recorded how long each solution remained under 1 degree celcius. Before the experiment, it would have been obvious to me that the best results would have been given by the 6g sample (enough for a saturated solution). However, our best result was given by 4g, but i cant understand why. Was it just experimental error? Or will excess ammonium nitrate cause less heat to be absorbed? All help greatly appreciated, Thanks, Dan.