See also Rudi's post #71.
You need to find out if you have:
(1) Sodium metaborate 4-mol in which case use the amount specified by Mark, or:
(2) Sodium metaborate 8-mol (this is also known as Kodalk)in which case multiply the amount specified by Mark by 1.354, eg 2.2gx1.354=3g
The quote from Ryuji is about 2 crystalline forms of the same substance,you are correct to say they are the same when dissolved, in this context it is only of academic interest.
Thank you Rudeofus and Alan. The supplier of my sodium metaborate (Vanbar in Melbourne) who package bulk chemicals have called it Kodalk so it should be the 4-mol. I will try to accurately measure the solubility which might determine which version I have.
No, see post #74, it is thought Kodalk is the 8-mol.
8-mol is NaBO2.4H20 which used to be written Na2B2O4.8H2O and called sodium metaborate octahydrate.This agrees with The Darkroom Cookbook p177 which gives the composition of Kodalk as sodium metaborate octahydrate, ie they use the old name.
If you have Kodalk the weight of metaborate given by Mark has to be multiplied by 1.354. as he uses the 4-mol compound.
richydicky: I owe you an apology! I noticed your question months later when this topic of 4-mol/8-mol came up again, and saw that I had not answered it. I must have overlooked it, being distracted or in a hurry. Sorry about that.
Originally Posted by richydicky
Here's a link to the earlier discussion about this topic which Alan has referred to:
I'll update the formula to specify 2.2g of 4-mol, or 3.0g of 8-mol sodium metaborate.
The question of 4 mol vs 8 mole keeps coming up! The differences are in buffer capacity and pH, both of which are different for these two compounds when used at equal weight. The pH difference is tiny, but meaningful and the buffer capacity is also small. The former is changes contrast, speed and / or development times while the latter has a tiny effect on sharpness and upper shoulder.
Which doesn't surprise me in the least. Given that the metaborate ion is generally described as BO2-, one would assume that the general nomenclature would distinguish between 2 mol and 4 mol. With the historical context in mind it makes sort of sense to have 4 mol and 8 mol, but people entering the field are likely confused. If I were to formulate a recipe today, I'd either start with Borax and NaOH/Na2CO3, or state the exact compound in my recipe NaBO2 * 2 H2O (or NaBO2 * 4 H2O), and maybe state that the compound is sold as Sodium Metaborate 4 (or 8) mol.
Originally Posted by Photo Engineer
It's confusing. Even the manufacturer gets confused. If you go to the two links in post #71 and open the links to Product Data Sheet you will find that on page two of each (top right hand column) that the same molecular formula is given for both compounds. One of them is wrong, of course.
I'm thinking of trying to ascertain which of the metaborates I have. I note that their solubilities in water differ, so I'll try to dissolve the one that's most soluble at 20degC and if it doesn't all dissolve I'll add water to see if its solubility matches that of the other one.
But tell me, I'm used to solubilities expressed as g/L of solution (or 100mL of solution). The product data sheets show solubilities as "percent by weight." So does this mean that x grams dissolves in 100mL of water to make an amount of solution that's probably not 100mL?
Determining the solubility of a compound can be a time demanding procedure, I'm not sure you're ready for this. Try dissolving 359 g/l Sodium Chloride if you don't believe me :munch:
If you get the stuff from a reputable source, they should be able to tell you exactly what they have, possibly even a CAS number which would completely eliminate any ambiguity. It's their business after all. The biggest problems come from published formulas which carelessly state "Sodium Metaborate" instead of the exact compound to be used, and no solubility test is going to help you with these.
AAAAAAAAAAAAAAA! I scream every time someone asks about % which is about once a month.
There is weight / weight, weight / volume, volume / weight, volume / volume and thus you see how solutions are "written up" in the chemical literature when % is to be expressed.
True % is, for a 10% solution of a solid in water, 10 g of solid and water to 100 ml for wt/vol, or 10 g of solid and 90 g of water for wt/wt.
It goes on. All of these different methods exist for handy use of viscous or organic solutions, especially in the dark.
I asked about this last month, so you were due for another. :)
Originally Posted by Photo Engineer
Anyway, D316 is passing more tests:
- It can be stored in the refrigerator with no precipitation.
- It can be stored in the freezer with no precipitation. When frozen, I believe it will last years.
I'm starting to test various films with D316, and FP4+ did fine. Its density-curve matches XTOL, shown below.
The curves are close enough. I think using a dev-time of 16.25 minutes (instead of 15.7) would be an excellent match. But I ran out of HP4+, so it's time to give Freestyle some business. BTW, you'll notice all my graphs have a small inflection at X=1.5. That's because the illumination of my light-table isn't uniform, and 1.5 is the transition between the two rows on the Stouffer chart. For comparisons with frames shot the same way but developed in XTOL, it makes no difference.