problems with Pyrocat HD

I mixed up my first batch of pyrocat h-d a little while back using this formula. http://www.jackspcs.com/pyrohd.htm

Part B calls for 100 grams of Potassium carbonate in 100 ml of water. How on earth are you supposed to get that much potassium carbonate into solution?

Any info will be helpfull.

Christopher Breitenstein

You can't, so stir in just enough additional water to dissolve the entire 100 grams of potassium carbonate. You should end up with a total solution volume of about 133.33 ml. This will give you a solution that contains approximately 0.75 grams of potassium carbonate in each ml of the B solution. (The same as 750 grams of potassium carbonate dissolved in a total solution volume of 1000ml).

Sandy King posted these instructions on APUG:

Stock B
Distilled Water -- 750ml
Potassium carbonate -- 750g
Add slowly while stirring the potassium carbonate to the water. Should make a total of about 1000ml. There will be an exothermic reaction that will cause the solution to warm up as you mix it.

You can use a variety of dilutions. I generally recommend 1:1:100 for silver papers and 2:2:100 for alternative printing but other dilutions may be better for specific purposes, for example 1.5:1:150 for stand development, 5:3:100 for very low contrast scenes with alternative processes, etc.

See: (there was a url link here which no longer exists)

It's much easier to just purchased the premixed Pyrocat-HD liquid part-A/part-B bottles.

They last a very long time and will save you time and headaches.

That original instruction called for 100 grams of Potasssium carbonate plus 100 ml of water.

Since that is a very "un-standard" way of putting it, it caused a lot of confusion. More recent instructions will call for 75 grams Potassium carbonate, and water to 100 ml.

One way to get stuff into solution is to be patient. Measure it out, put the water in and put it on the shelf. Shake it every day or so and it will go into solution.
If you do a little planning this works out pretty good.

30-45 minutes with a magnetic mixer takes care of the problem. At first it seens little is happening, but as the solution warms, the powder is dissolved.

My earlier post was incorrect. Potassium Carbonate's solubility in 20°C water is 112 grams/100 ml and its Aqueous solution pH is 11.6

If your stuff is reasonably pure anhydrous Potassium Carbonate, 100 grams of it should dissolve in 100ml of distilled or deionized 20°C water. If all of it won't dissolve, maybe you got sodium carbonate instead of potassium carbonate??

Sodium Carbonate's solubility is lower - 45.5 grams/100 ml in 20°C water.
Sodium Carbonate's aqueous solution pH is 11.6.

You can make up your Pyrocat "B" solution with sodium carbonate - but you will need to use more of the B solution when you mix the working developer.

Tom Hoskinson said:

My earlier post was incorrect. Potassium Carbonate's solubility in 20°C water is 112 grams/100 ml and its Aqueous solution pH is 11.6

If your stuff is reasonably pure anhydrous Potassium Carbonate, 100 grams of it should dissolve in 100ml of distilled or deionized 20°C water. If all of it won't dissolve, maybe you got sodium carbonate instead of potassium carbonate??

Sodium Carbonate's solubility is lower - 45.5 grams/100 ml in 20°C water.
Sodium Carbonate's aqueous solution pH is 11.6.

You can make up your Pyrocat "B" solution with sodium carbonate - but you will need to use more of the B solution when you mix the working developer.

Click to expand...

Yes, I was going to comment on that. In theory ite should not be at all difficult to mix 100 grams of potassium carbonate with 100 ml of water, even though this may not be a standard way to describe mixing. But what you get, as you indicated is about 130 ml of total solution, or a 7%% potassium carbonate solution.

The fact that so many people have experienced problems with this mixture suggests on of two issues. First, maybe they did indeed get sodium carbonte instead of potassium carbonate, which has a much lower solubility. Or, there is the issue of delisquescence. Potassium carbonate can absorb or release a lot of moisture from the air, depending on humidity.

Sandy

FWIW I had no trouble dissolving 750g of potassium carbonate in tap water at room temp to make 1000mL of solution. Sandy's post above was probably supposed to say 75% not 7%%.

750 g of potassium carbonate that has absorbed atmospheric water should dissolve even more easily, but it won't be the correct strength.

One could heat the carbonate to drive off water of crystallization. If the carbonate is purchased as anhydrous and kept in a closed container, the maximum amount of water it could accumulate is the amount that would be in equilibrium with the water vapor in the container, which is probably quite small. Each time you open the container, the partial pressure of the water vapor therein may change, but the weight of water introduced or leaving the container must be quite small compared to 750 grams. As an excercise, you could look up in an air conditionig chart the weight of water per weight of atmosphere for any given temperature and humidity and do enough calculations to convince yourself that the change in water of crystalization is not a great concern for most practical photographic uses.

As a matter of interest, note that the 75% solution in terms of weight of solute per volume of solution in Metric units will not be 75% in English unite. It will be 50% in terms of weight of solute per weight of solution in Metric units.

I had blanked out on a 5# pail of potassium carbonate that I had stashed here and ordered some more on a recent chemical order.... When I tried to make up a batch of B solution with the new stuff, I ran into solubility troubles. I needed to go to 1/2 of the normal potassium carb to get it into suspension. I then started questioning my past practices, etc as it hadn't been an issue previous to this. I then found the extra stash of the old supply and remixed with that and found I could get 150gr into 200gr water as I'm accustomed to which reminded me of this thread. I thought I'd pass on my experience in case it meant anything to someone fighting with this same thing.

Reviewing this thread brings a question to mind. Why can't you mix 50g Potassium Carbonate (anhy.) with 100 mL water and use Part b as two in place of one: 1+2+100?

Bruce (Camclicker) said:

Reviewing this thread brings a question to mind. Why can't you mix 50g Potassium Carbonate (anhy.) with 100 mL water and use Part b as two in place of one: 1+2+100?

Click to expand...

You can. Or you can mix 25 grams of potassium carbonate in water to make a 25% solution and dilute it 1:4:100 for the working. In fact, many people substitute sodium carbonate for potassium carbonate and mix a 20% solution, which they then dilute 1:5:100 for the working.

I just personally prefer the more concentrated stock solution and have never had any trouble at all in mixing up a 75% potassium carbonate solution.

Sandy King

Craig:
I'll bet you got sodium instead of potassium. As was mentioned, you should be able to dissolve 112 g of the anhydrous in 100 g water at 20 C or 146 g of the K2CO3.2H2O. A saturated solution of either will have the same number of molecules of K2CO3/CC. If you cannot dissolve 100 g/100 ml water, it must be the sodium.

Follow-up on this...

I contacted the vendor via email, related my situation and received a replacement 5# jug right away. This one works as I am accustomed to and I have no explanation for what really happened. A film test gave me close to normal results but slightly thinner negatives...actually normal shadow separation but more of a compensated look in the highlights. Who knows, maybe I'd prefer it for some things! Actually, it's hard enough chasing the variables without adding potency issues into the mix....

Thanks for the responses. This is the sort of little episode that gets you questioning your routines and procedures and I'm happy it was so easily solved.

A quick add.... This is an unfortunate title for the thread as it doesn't really relate to problems with PyroCat but I added my post to this older thread as the real topic was dealing with the solubility issues.