I really love this re-crystallization method for its simplicity, but not 100% satisfied with color.
View attachment 17951
This is the best result I was able to get with this method at point 107C. It is not bad, but still not perfectly white transparent.
This time I checked the weight of water I drained.. It was 2 gr per 50 gr of salt. Rest of water evaporated naturally.
I applied Raoult to this data and got the result below. I shall consider atmospheric pressure as well. As for the sea level water boiling point is 100C, but for 700m altitude it is 98C.
So the shift for sea level is 7C, for 700m - 9C while heated till 107C.
mw = 0.52 * ms * 1000 / (dT * 229.7)
mw (sea level) = 0.52 * 50 * 1000 / (7 * 229.7) = 16.2 gr.
What if I try to add some side solvent, with more high than water boiling point and less than water solubility? The target is to add more sovlen to slow crystallization down and decrease nucleation. Hopefully, more liquid can trap more impurities with bigger size and purity crystals in result?
Glycerol for example dissolves the salt half much as water and has boiling point at 290C.
If I stop crystallization with the same volume of water, then there will be 5 * 1.26 / 16.2 = 38.8% glycerol water solution with boiling point 117C without salt.
Then, when salt added, Raoult increases boiling point as well with another 8-10C - I need to know ebullioscopic constant of such mixture to calculate it precisely, but probably it shall be more than 0.52 and less than 1.5.
So, probably I shall heat chloride solution till 125-127C with resulting 50 gr of salt in 16 ml of water + 5 ml glycerol solution for better result?