Amm. thio in powder form

Hello PE, Mr. Suzuki, Ole and other chemists: ammonium thiosulfate is now available in powder form from the Formulary. This will save some $ on shipping, however, I remember a thread somewhere about some problems with powdered amm. thio. If memory serves, the stuff sucked up water from the air faster than a dehumidifier on a humid day and turned into concrete. Any other problems with it being in powder form? Is it worth buying in this form?

http://www.photoformulary.com/Deskt...tabindex=2&categoryid=19&selection=0&langId=0

Let me check my math, buy five pounds ($44.75 + shipping), mix with water to make 1 gallon of 60% (available mixed from PF for $16.95 + shipping). Does it cost $27.80 to ship?

Seems like unless you're using the Ammonium Thiosulphate for something else, it not cost effective.

They would have to sell the powder for $3.39 a pound to equal the cost of the liquid, not considering the shipping differential.

Your math appears close enough for hand grenades and maybe even for TF-3 fixer

Living as I do at the Edge of the Earth, shipping one gallon of liquids from either PF in Montana or from my only Canadian source of 60% ammonium thiosulfate in Quebec (thousands of miles away), shipping is over 20 bucks.

It'll really start to make sense if I can weasle a better price for larger amounts...

Murray

For best stability (shelf life), it's better to keep ammonium thiosulfate in 60% solution, with 1% or more sodium thiosulfate or sodium sulfite mixed in. If you are making a neutral or alkaline fixer (see the formula section for my neutral rapid fixer formula), it's best to mix the fixer concentrate and keep it in this form. Technical grade ammonium thiosulfate usually comes in as 59-60% solution with about 1% sodium.

As for the shipping cost, I am not certain about Canada and Mexico, but for other countries, Digitaltruth sells raw chemicals and they ship by surface to save shipping cost, if you ask. I think the surface ship option should be in their shopping cart system, but if you don't find it, email them about it.

I've also heard it's "hygroscopic" or something like that and will turn into "concrete" very quickly if not handled properly. Any comments on that?

timeUnit said:

I've also heard it's "hygroscopic" or something like that and will turn into "concrete" very quickly if not handled properly. Any comments on that?

Click to expand...

I think the actual result is "slush".

However, if packed properly, there is no problem.

The benefit lies in the ability to ship a well packed solid without 40% of it being water, for a lower rate, to some remote locations. We have seen a number of people seeking solid ammonium hypo for just this reason.

Another advantage is the ability to mix solutions that are more concentrated than you can otherwise get with the 60% solution. This would mainly concern those who want to run experiments with fixers, like myself.

If kept sealed tightly, it will keep quite well for a surprising length of time as a solid. In SEA, we learned that there is a way to pack even sodium hypo that prevents absorption of moisture from the air. Sodium hypo is also hygroscopic and quite unstable in solution as we all know. If you are concerned, pack the entire bottle in a baggie with a zip lock. If possible, drive out the air with a blast of an inert gas.

PE

The problem with hygroscopic solids is that it's hard to be sure just how much you have. If you are absolutely sure that the material was entirely dry when packed and if you can keep the dry conditions in the bottle during storage and use, you can use these materials pretty well most of the time. Otherwise atmospheric moisture will continuously change the effective formular weight and make measurement difficult. Fortunately. fixer isn't too fussy about exact measurements. If you live in a dry area, you could give the solid ammonium thiosulfate a try, with the precautions noted by PE. If you frequenly get 70+ percent humidity, I'd be cautions. Mixing one or two gallons of 60% ammonium thiosulfate is probably a good idea - you open the bottle less often and give it less chance to get wet. It would be best to dissolve the entire stock as soon as you get it. While sodium thiosulfate (sodium hypo) suffers the same problems as the ammonium variety, it is much less hygroscopic than ammonium thiosulfate. In SEA we did manage to keep hygroscopic lab reagents usable with only occassional problems using techniques like PE suggests (although some of them required dessicators), but the weather there was really a lot less brutal than some of the US eastern seaboard during the summer.

The powdered ammonium thiosulfate (anhydrous) I buy from VWR (only supplier of raw chemicals in Norway) doesn't seem to be hygroscopic. At least it's still a free-flowing powder.

I bought 5 kg some years ago. I'm using it slowly, since I use OF-1 for "larger amounts" of fixer - the ammonium thiosulfate tends to be used diluted (50%-ish) in 20g batches dumped straight into spent dilute film developers instead of "stop and fix". It works great with Beutler's / Neofin and FX-2; OK with Rodinal.