Quote Originally Posted by Murray Kelly View Post
Now, there's a difference! Not like the almost too close to call Microdol-X comparison in the other thread on the 'dead' metol.
I have to say, tho, I've never used Rodinal that strong and don't know if dilution is a factor. The tonality matches but the detail isn't there. SPF-3 looks good to me.

Given the unusual solubility (amount and curve) my idea was to fractionally crystalise out the tetra and leave any more soluble contaminants in the supernatant. I didn't do it in the end. I merely weighed the plastic pots and contents, making a note under them and will reweigh when I need to open another one up for use. This assumes the contents were indeed tetra as stated on the MSDS to start with.
The borate part of decahydrate and pentahydrate are identical. The difference is in the amount of water of crystallization. A saturated solution of either one at a given temperature contains exactly the same number of Na2B4O7 molecules. Once you have a saturated solution and have decanted the clear liquid, there is no point in trying to recrystallize the contents, because you are then back at the beginnibg. You still are not certain which of the crystals are pentahydrate and which are decahydrate. You still have to weigh the crystals to make any use of them, whereas the saturated liquid has a known content of the decahydrate per unit of volume and can be measured out with a graduated cylinder.

The terms "pentahydrate" and "decahydrate" have no meaning in solution. However much water of crystallization was taken into a borax solution becomes part ot the solvent water. All you have in solution is Na2B4O7 molecules and H2O molecules. The molecule that entered as the pentahydrate carried 10 molecules of water with it. The molecule that entered as the pentahydrate carried 5 molecules of water with it. Now we have 2 molecules of Na2B4O7 floating around in 15 more molecules of water than we had before. There is no way we can tell which of the borate ions came in which which of the water molecules.