You are doing your measurements qualitatively using the Mark I Eyeball which in your case is now over 80 years old IIRC.
I did mine with the IB sensitometer and the Macbeth densitometer and did it qantitatively.
I trust mine, and I trust the differences that I have seen. Papers can sense as little as 100 milligrams difference in bromide or chloride concentration in a liter of developer. It affects speed and curve shape both. In some papers, it affects fog as well.
Yes, but I was talking about film. I do use metaborate in paper developer, but that's a different animal from the one we've been discussing. I do have a densitometer that I designed and built that can read to .005. Besides, if the tech borax meets specs, a saturated liter would have at most about 0.028 grams of sodium chloride.
Well known? - didn't you just point out that there are two different specs for the same grade of borax? Granular and powder - both called Technical Grade, have differing specs?? That's pretty precise!
Also, you say,
That's not the highest grade that you have seen. Technical grade is usually considered the lowest grade. Surely you read the assay that Mick listed for the results of his ACS Analyzed Reagent Grade Borax - it listed "Assay = 99.101%". http://www.apug.org/forums/forum37/4...tml#post556946
Let's think about that for a second to let it sink in... One grade has a precision of 5 digits, the other grade has a precision of 10%. Now which one should we consider to be the higher grade? I hope you answered this one by saying "AR Grade" to yourself.
The highest grade I have seen from Rio Tinto specs is NF, a pharmaceutical grade, which lists only heavy metals at <20 ppm. The difference between Rio Tinto Tech granular and powder is ONLY in the water insoluble particles, which are <400 ppm in the granular and none in the powder. The variance in measurement of percent borax decahydrate is in the water content, which will vary with storage conditions due to changes in humidity. the same variance can occur in any grade, including AR.
Your AR grade assay was for a particular sample of known hydration
If a cheapskate is using alternate-sourced borax instead of 'photo grade' (or photo company supplied), for cost reasons, then there will be a limit to how much lab refining the cheapskate is able/willing to spend time/money on. A 4 liter Pyrex beaker probably costs more than some of my other stuff and more than my chemicals combined.
I may be in the cheapskate category, but I'm sure I spent more buying bulk chemicals than I could have buying packages of developer, because I would have more fun with the DIY approach.
I DO find the discussion of the science interesting, however.
The highest grade I have seen from Rio Tinto specs is NF, a pharmaceutical grade, which lists only heavy metals at <20 ppm. The difference between Rio Tinto Tech granular and powder is ONLY in the water insoluble particles, which are <400 ppm in the granular and none in the powder. The variance in measurement of percent borax decahydrate is in the water content, which will vary with storage conditions due to changes in humidity. the same variance can occur in any grade, including AR.
Your AR grade assay was for a particular sample of known hydration
Pat - Did does Rio Tinto Technical Grade Powder really say "none" for the insoluble particles? That surprises me as there should be a limit of some sort - i.e a value given in parts per million. As an analytical chemist, I can say that there is always going to be a little of something in most everything... unless you are talking about homeopathic medicine. Did it really say None detected or something, and that is based on the method of analysis, but really doesn't mean that there is "none". Just that that test can't detect any.
The AR grade assay had absolutely nothing to do with a "known hydration". Infact, I doubt the hydration was even tested for. It was an "assay", a measurement of the material of interest.
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If a cheapskate is using alternate-sourced borax instead of 'photo grade' (or photo company supplied), for cost reasons, then there will be a limit to how much lab refining the cheapskate is able/willing to spend time/money on.
Murray, I'm with you. But it is fun and interesting to discuss the various ways that we can devise to make our technical grade chemicals end up costing more than just buying the recommended grade in the first place.
The highest grade I have seen from Rio Tinto specs is NF, a pharmaceutical grade, which lists only heavy metals at <20 ppm.
It's interesting that NF grade only is concerned with heavy metals (as quoted my Pat), and not any of the other substances that the other grades are spec'ed for, like chloride or insoluble matter. It really does point out the differences in the grading system for chemicals and how one should consider these things when chosing a particular grade for a particular use.
It's interesting that NF grade only is concerned with heavy metals (as quoted my Pat), and not any of the other substances that the other grades are spec'ed for, like chloride or insoluble matter. It really does point out the differences in the grading system for chemicals and how one should consider these things when chosing a particular grade for a particular use.
I don't know that heavy metal, expressed as lead, is the only impurity they are concerned with. It is the only one they listed. There is also a grade SQ for special quality that is granular and has very low allowable maximums of chloride, sulphate and iron. I imagine that the analysis for insoluble material is like the one you described a while back. If you can't see it in the solution and all the solution passes through the filter, whatever is insoluble must be negligible. I figure that if the Powdered Technical grade showed observable insoluble stuff, there would be a comment like < whatever the filter is specified to retain. The powdered and granular have the same specs in the soluble impurities.
I still don't know the ANSI Specifications for Photo Grade, but have applied for a copy. I don't expect to hear from them until after the holiday season.
I want to make sure everyone knows I am not expecting to produce chemically pure borax by my purification. It is a fractionation method, and since each fraction is less than 1, the final product cannot reach absolute purity until the amount left is 0.
I do not see, given the nature of borax, how a large amount could be stored in a bin so that any random sample would have the same hydration as any other. The manufacturer says that when humidity is lowered some of the borax that started as 10 mol will become 5 mol or even anhydrous. If the humidity becomes higher, the hydration moves back to 10 mol causing some clumping. It is not like NaOH which will form a puddle if left open to high humidity, so I suppose that if your borax were stored at high enough humidity it would all settle out at 10 mol and the percentage of borax decahydrate would simply be 100 - impurities. But if there is not enough humidity in the atmosphere to maintain the decahydrate, what you weigh to be 100 grams of borax decahydrate could be equal in sodium tetraborate content to more than 100 grams. If you purchase it as AR grade, and accuracy of measurement accuracy is critical to your purpose, then it would be well to make sure the the humidity in your storage container stays at the proper value. I don't know what that value is because most uses in developer are not very critical as to weight of borax, however critical they might be in ppm of impurities.
I got the ANSI specs for Photography chemicals sodium tetraborate, pentahydrate and decahydrate, 3 pages ata cost of about $21. In a nutshell, the summary of requirements is:
Assay, Pentahydrate or Decahydrate......101% min, 105% max.
Heavy metals (as Pb)......0.002% or 20 ppm.
Iron (Fe)......0.003% or 30 ppm.
Carbonate......To pass test.
Reaction to Ammoniacal Silver Nitrate.......to pass test.
Appearance of solution........to pass test.
The tests are described in great detail. Kirk or PE could perform them. Most of us have not the equipment nor the skills to perform them.
It appears that the specs would be met or exceeded by the NF grade described at www.borax.com, and the SQ grade would come very close.
You will notice that the minimum assay is greater than 100% and less than 105%.
I have read the spec and it is rather trivial both in content and in testing methodology.
The problem is that my time is more valuable to me than the cost in time and chemistry to run the tests. That is one reason why I prefer to buy the best to start with.
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