I have been conducting an experiment for a school project, (removing metals from water)I added 50 grams of sulphate of potash to 2 litres of water, then allowed it to dissolve for a 24hrs.
On two occasions, during the 24hrs, I measured out a litre and weighed it, the potash caused it to weigh 1.018kg.
I then transferred 1.4L of heavy water to a new container and added 100ml of liquid poly-aluminium chloride (which weighs almost exactly the same as water). So, assuming no floccing, the theoretical weight of 1L of this new mixture was
$$1/15*1 + 14/15*1.018 = 1.0168$$
kilograms. After stirring the new mixture, I immediately measured one litre, and it weighed 1.008kg (meaning that the alum had worked instantly).
After allowing the alum to react for a day, I measured again. However, I was surprised to find that it weighed 1.021kg. I cannot understand why it has gotten heavier. (There is powder/crystals that has/have clearly sunk to the bottom).