Pyrocat HD Part B

Hi All,

Haven't mixed any part B in ages and today missed a batch with Anhydrous potassium carbonate.

I went with the standard for 500ml which is 375ml distilled water and 375g of potassium carbonate and water to 500ml.

However i used the anhydrous carbonate which makes me think i screwed up the amounts and should've used 250g for 500ml end product.

Am i right in thinking this ? If so will i be ok just adding more water to make it 50/50 ?

Cheers,

S.

375g k.carbonate anhydrous in solution is equivalent to ca. 450g of the sesquihydrate. Pyrocat bath B off the top of my head is a 75% solution; I assume the sesquihydrate is intended, but you'd have to check. If so, that would mean your 375g anhydrous carbonate should make a 600ml volume pyrocat B.

ssharp said:

and should've used 250g for 500ml end product.

Click to expand...

I don't think so, assuming B is 75% w/v of the sesquihydrate.

Pyrocat HD Patrt B is 750g Potassium Carbonate (anhydrous) dissolved in 1 litre of watrer, So 350g un 500ml is correct.

Ian

The amount is correct, but does it make sense to mix such a large amount?

lamerko said:

The amount is correct, but does it make sense to mix such a large amount?

Click to expand...

He's mixed a small amount 500ml, I always mix 1 or v2 litres at a time.

Ian

Whether you have bought anhydrous or sesquihydrate, be aware that potassium carbonate is deliquescent, that is, it absorbs moisture from the air. Some compounds seem quick to do so, others seem to be slow. Descriptions of potassium carbonate can include the observation that it can become noticeably wet, so if it started as anhydrous it would have passed through stages of hydration on the way to becoming obviously wet.

In my case, I bought 20kg of anhydrous in a plastic lined paper sac. I shared this with some others. Some I kept in the original packaging, the top tightly rolled up and clamped. Other went into a plastic bag inside a screw top kitchen canister. Not the finest storage for analytical chemicals, but I thought not too bad for my purposes. The quantity used in developers isn't ultra critical, especially as I don't replenish. (mainstream Ilford formulas substituting sodium for potassium salts for solubility making it easier to make concentrated stock, easier to store in a tiny darkroom and probably better keeping qualities, and Pyrocat-HD). The climate here is not extreme.

After changing film forced on me by the discontinuance of Neopan400, I did some testing of my new choice, HP5+. Initial tests with Pyrocat-HD were a bit disappointing. I tried Phenidone-A instead of Dimezone-S, and it made no difference. Then I tested the density of my Pyrocat Part_B and found that I needed x1.26 of my carefully measured Part_B to equal the intended amount. I wrote about this in another post around here. The powder still is fine and flows freely,

It has got me a little closer to my expectations with HP5+. However, lots of people tweak the proportions when mixing Pyrocat for reasons of control, so maybe it doesn't matter so much, as long as you are consistent.

Apparently (Oxford Resources) it can be dehydrated at above 130degC.

john_s said:

The powder still is fine and flows freely,

Click to expand...

If it would have absorbed water, it would have caked. Moisture absorption does not sound like the explanation of your observation.

koraks said:

If it would have absorbed water, it would have caked. Moisture absorption does not sound like the explanation of your observation.

Click to expand...

Maybe it was contaminated. Sealed in factory packaging, but it was Chinese. I've had a bad run with Chinese products lately.

In all honesty I think the explanation is elsewhere. There's not an awful lot that can go wrong with potassium carbonate.

koraks said:

In all honesty I think the explanation is elsewhere. There's not an awful lot that can go wrong with potassium carbonate.

Click to expand...

I'll make it up again being as careful as possible with weighing, not that there was much of a possibility of much error the first time. I have calibration weights for my not cheap lab scales, and a volumetric flask.

I believe the pH of the carbonate solution should be over 11.6, bicarbonate is 8-8.6.