So, here I had just made a good, pure bluish-green crystal (wait… I had seen this on a TV show before) of iron sulphate. This came around based on my frustration of having to filter my developer several times with sludgy, dirty developer before (see my previous blog on that here). Vitriol is an old name of sulphuric acid, which referred to a number of sulphate types. As for iron sulphate, or copperas, is green vitriol.
Though it’s not essential to do this purification steps, I do have an hour to spare in a day to do this in small batches, in a way, it’s like ‘farming’ for pure crystals. It’s essentially ‘re-activate’, or replenished the oxidised iron sulphate with diluted sulfuric acid, aiming simply to use the old stock that came bad, or went bad. Or another way of purifying if you’re using moss/weed killer type.
I know it’s cheap, dirt cheap to buy fresh iron sulphate. But what about those leftovers that had been oxidised? Or impure? I know compared to the rest of other ingredients in wet plate collodion steps, the issue could be resolved with greater quality filter (i.e.-Buchner vacuum funnel, or with high grade filter).
But doesn’t harm to do some lab session every now and then. Of course, you could make your own Iron sulphate with steel wool mixed with sulphuric acid as well (refer to the link reference below), which the steel wool requires a proper wash with acetone, but I wasn’t in much mood to prepare a proper space for it as it does make a bang for its low degree flash point and prone to combust with little spark around its environment.
And the usual warning:
Though, with imperative warning I must give before considering to venture into this, you will be handling acid and this will requires proper safe handling and care (ready the MDSS). I will not be responsible for any injuries, fatalities, accidents, or incidents which could occur from this blog entry. Or even guarantee the satisfactory in the results of solution’s quality arrive from this chemical experiment. Hence, this disclaimer must be presented and you have been warned.
This is what you would need to have/work with:
- The usual safety goggles, gloves and measuring labwares, digital scale.
- Old Iron/Ferrous Sulphate.
- Erlenmeyer flasks or any borosilicate container.
- Battery water** (with 37.5% sulphuric acid content, not the de-ionised water)
- Funnel and filter
- alcohol lamp
- Distilled water.
- Container for air drying (I usually use fishing ice box)
- A lot of silica gel
- Potassium Carbonate powder
- Sodium Carbonate (Na2CO3)
**A little story on this, I had looked around local stores (i.e.- Halford, local car parts retail) for battery water which contains sulphuric acid. This stuff is very common for anyone using old type of car batteries to replenish or replace the battery water. But one store manager had gave me an ignorant look and said, “look, we don’t sell any of “acids” here, you have to go to chemist to buy them!” said him with an attitude. While I peered behind him which was racks of car batteries, which just as well telling me they’re filled with lemonade juice then. Bah! Off I go to a local garage, which they have plenty to spare and costs almost nothing.
For this example, I would work with 15 grams (usually I go for 50 grams per session), just to show such quantity would make the crystallisation a bit more faster.
The next step is to add it into 40mL of distilled/de-ionised water.
Stir it till most of the iron sulphate dissolved, it would look like grey sludge.
Next, add 10mL of 37.5% sulphuric acid. (or this could be mixed earlier, which is to mix 10mL of sulphuric acid in 40mL distilled/de-ionised water, which makes it a 9.38% solution, then add the 15g of iron sulphate)
Stir & agitate the flask. As there will be some stubborn bit of iron sulphate left, which the next step will take care most of it.
Fire-up the alcohol lamp, and while agitating the flask, carefully heat the flask.
It shouldn’t be boiling, at most steaming (around 70-80° Celsius) just to speed up the reaction.
Once the entire iron sulphate dissolved, and the solution turned green / bluish green, you could turn it away from the heat and keep agitating to cool it off.
Pour it off in a filtered funnel into another opened container, the wider the surface of the solution, the better for it to properly crystallise.
Then, chuck it in the box container (I use a fishing box), which are filled with silica gel, and in the box with a small opened bottle/container filled with potassium carbonate powder (about 100 grams or so would do). The potassium carbonate powder will neutralise any acidic fumes from accumulating.
Leave it for 1-2 weeks, depending on the surface area of the solution that rests, how good is your silica gels, and the air tightness of the container (a desiccator vacuum chamber would be excellent for this).
Light green crystals would form, usually in a large chunk and many little bits on the sides.
Scoop the crystal out of the solution, which is yellow. Remember, this is still acidic (sulphuric acid excess). You could pick the crystal out with a stainless steel tweezers and wash the crystals off with chilled distilled water to rid any excess sulphuric acid on its surface.
After the crystals taken out, neutralise the excess acidic solution with a dash of Sodium carbonate. Check the pH before disposing properly.
Then chuck the crystals into another flask container, and into the silica gel box to dry it off.
Crush the crystals with mortar & pestel for your developer use.
Note: This preparation had a yield of 50-60% of pure iron sulphate crystals as the weight measurement for the crystal was at 8.65 grams (from 15 grams of dirty iron sulphate), the loss is due of few factors; during the funnel filtration, and left out smaller crystals which were not worth scraping out.
http://www.crscientific.com/ferroussulfate.html, reviewed 1st March 2015