Iron Hexacyanoferrate: The Blueprint for Fun

It's Christmas break and while I don't really stop doing research I feel a little justified in taking a little time for myself. Today I decided to make blueprints and cyanotypes. What, you may ask, do blueprints and cyanotypes have in common? The answer is Prussian Blue (PB). We'll get into the chemistry of PB later, but first I'll show you what I made.


Several months ago I found this image on the web and I decided that it would be my first attempt. I chose it for two reasons:

1. It's only black and white, no grey scale, so I'm not going to need to worry about over developing it.
2. I thought that the steampunk image would be appropriate for a process that was developed in the 19th century.

To make this image I took a solution of iron ammonium citrate and potassium ferricyanide and coated a piece of paper with it. I then let it dry in the dark. The coated area looked yellow green. I then printed the image on a transparency and taped the coated paper to the back of the transparency. I then taped the paper and transparency to the window in my office. After 12 minutes I had noticed that the yellow green color had darkened to a more brown color. I then took the transparency off the window, removed the paper and ran it under deionized water to wash off all of the unreacted chemicals. It is at this point where the blue color really developed. Encouraged by the positive results I decided to make a second harder image.
The second image I made was a little more complex for a few reasons:

1. It is a grey scale image and so I needed to worry about contrast in the image.
2. I needed to make a negative of the picture I wanted to reproduce.
3. The sun went behind a cloud and so my previous time calculations wouldn't work.

As you can see this image is much more pale than the first. But over all I consider it a resounding success.
I said earlier in the post that I used a solution of iron ammonium citrate and potassium ferricyanide to make the light sensitive solution. The actual solutions are 0.95 M Fe(NH₃)C₆H₈O₇ and 0.30 M K₃[Fe(CN))₆]. If you count the electrons in the compounds you will notice that the iron in both the Fe(NH₃)C₆H₈O₇ and K₃[Fe(CN))₆] is in a +3 oxidation state (this can be indicated by superscripted roman numerals K₃[Fe^III(CN))₆]). Once mixed, the light sensitive Fe(NH₃)C₆H₈O₇ absorbs a photon causing an electron to be transfered to the iron atom reducing it to Fe⁺². This ferrous (Fe^II) ion then reacts with the hexacyanoferrate (Fe^III) to form the insoluble Prussian Blue:

K⁺(aq) + Fe⁺²(aq) + >[Fe^III(CN)₆]^-3(aq) ---> KFe^III[Fe^II(CN)₆](s)

If you look at the oxidation states you can see that there was an electron transfer between the hexacyanoferrate anion ion and the ferrous cation. Interestingly for years people thought that they were making the KFe^II[Fe^III(CN)₆] salt which they called Turnbull's blue but which recently has been shown to spontaneously transfer an electron and form Prussian Blue. Prussian Blue comes in two closely related forms that are termed "soluble" and "insoluble". Soluble Prussian Blue has the form of MFe[Fe(CN)₆] where M is a monovalent cation, while insoluble Prussian Blue has the form Fe₄[Fe(CN)₆]₃. In both cases there is an Fe^III cation bound to an [Fe^II(CN))₆]^-4 anion. These names are somewhat misleading because both materials are very insoluble in water however the soluble Prussian Blue can be suspended in water making it look like it has dissolved while it is still just a suspension.
The crystal structures for Prussian Blue is shown below where the Fe^II is shown in red and the Fe^III in blue. The potassium ions sit in four of the eight octants arranged tetrahedrally.
For more information see Day's "Molecules into materials case studies in materials chemistry -- mixed valency, magnetism and superconductivity" page 190, or "A Blueprint for Conserving Cyanotypes" by Mike Ware.

Calvin Chemistry

My reactions didn't go as I had wanted one day and so to blow off a little steam I doctored this Calvin and Hobbes strip originally published on 03/06/91. My appologies to Mr. Bill Waterson.

Phi: A whole H of a lot cooler than Pi

Warning: This post contains no chemistry. Now with that off my chest I wanted to share something that I just discovered all on my own (That's not to say it wasn't known before I discovered it it just means that no one showed it to me.)

I want to make an original tessellation like M.C. Escher's. I then started sketching different regular polygons that can tessellate a plane. When I got to the pentagon I knew that it couldn't tessellate alone but I didn't have a good idea of what else I needed to make it work. So I started drawing pentagons. The first thing I drew looked like this:

I thought "Oh, it makes another pentagon. I could turn this into a fractal" and so I did and I made this:

I then wanted to know what fraction of the area of the large pentagon is taken up by the smaller pentagons. My train of thought went something like this: To do this I needed to find the length of the side of the new large pentagon. That's 2 times the first pentagon plus the space in between. The space in between is the leg of a triangle. The angle of the triangle is 36^o so half of it is 18^o. So sin 18 is 0.309, double it so that's 0.618. WAIT! If I add that to the one of the pentagon's sides that is 1.618 that is the Golden Ratio!

So, after looking on line all of these things were known before I started but I had fun discovering them.

Remember Remember...

Remember, remember the Fifth of November,
The Gunpowder Treason and Plot,
I know of no reason
Why Gunpowder Treason
Should ever be forgot.
Guy Fawkes, Guy Fawkes, t'was his intent
To blow up King and Parli'ment.
Three-score barrels of powder below
To prove old England's overthrow;
By God's providence he was catch'd
With a dark lantern and burning match.
Holloa boys, holloa boys, let the bells ring.
Holloa boys, holloa boys, God save the King!

Happy Guy Fawkes Day! I thought that today would be a great day to discuss gunpowder. From a very early age I knew that gunpowder was made from three things: Carbon, Sulfur, and Saltpetre. I knew what carbon and sulfur were but all I knew about saltpetre was that it came from bat guano. This did not stop me from sharing my vast knowledge of gun powder with my other geek friends "If only we had some carbon, sulfur, and saltpetre we this wall wouldn't pose any problems..."

I continued to dream about making my own gunpowder through my undergraduate time but I never made any even though I had access to all the chemicals. Many of my professors were happy to give me different chemicals for my own projects but I made a decision that I would never use any of the chemicals from school to make explosives. That way if something went wrong the school couldn't be held accountable in any way. During this time however I learned a lot about how gunpowder works. Carbon is the primary fuel in the reaction, sulfur is also a fuel but it also reduces the ignition temperature and speeds us the reaction, saltpetre is also known as potassium nitrate KNO₃ and provides the reaction with the oxygen it needs. A very simplified chemical reaction for the combustion of gunpowder is:

KNO₃ + 3 S + 8 C → 2 K₂CO₃ + 3 K₂SO₄ + 6 CO₂ + 5 N₂

We start with 8 moles of solids and end up with 5 moles of solids and 11 moles of gasses. While the solids take up very little room (a few cubic centimeters at most in a firework) the each mole of gas takes up 22.4 L of volume at stp. It is the rapid evolution of all of these gasses that causes an explosion.

My desire to make gunpowder went from dream to reality when I was at our local pharmacy picking up a prescription. While waiting I was perusing the shelves of vitamins and supplements (I always do this when I have the time because it's good to know what chemicals are available if I need them) I found a bottle labeled "Flowers of Sulfur" and then right next to it from the same company "Saltpetre." It had to be a sign. I bought both bottles and the pharmacist didn't even bat an eye. When I brought both of them home and explained it to my wife she was very understanding and asked me not to blow up our house or our son.

So with these ground rules I got down to business. I had two of the three and all I was missing was the carbon. I called all of the local pharmacies and apothecaries but none of them had any activated charcoal. So I set out to make my own. I knew that the best form of charcoal to use was from softwood charcoal but all I had was newspaper so I burned it and collected the ashes. I weighed out the ashes and used them as my limiting reagent. I weighed out the appropriate amounts of KNO₃ and S to make gunpowder (75% KNO₃, 15% C, 10% S). I put it all into the mortar my mother-in-law gave me and set about grinding it until it was a fine grey powder. I had done it, I had made my own gunpowder. To test it I put a little trail on the ground and I lit it. It burned wonderfully.

So while King James I and Parliament have nothing to fear from me there are some pumpkins around who might.

Edit 11/06: I made this video of burning Guy Fawkes in effigy last night using some of my gunpowder. I also made the wick which isn't very good.

Mole Day

Happy Mole Day everyone!

Atomic Mouse Traps

I'm a TA for a freshman seminar called "Beyond Fossil Fuels" in which we discuss energy and sources of energy. It is my job to come up with an interesting demonstration to illustrate the concept we are studying that day. Today we talked about atomic energy. I decided to use a demo that I had seen on Mr. Wizard years ago: The Mouse Trap Bomb. The story goes that this demo was developed by Walt Disney in the 40's to educate the public on how an atomic bomb works by demonstrating an atomic reaction. I don't know if this is true but I have found some journal articles from the American Journal of Physics that I thought were useful:

1. Sutton, R. M., American Journal of Physics, 1947, 15, 427-428
2. Manley, J. H., American Journal of Physics, 1948, 16, 119-120
3. H. D. Rathergeber, American Journal of Physics, 1963, 31, 62

This demo loosely represents what happens during nuclear fission. The mouse traps represent fissionable atoms while the ping pong balls represent neutrons. When a free neutron (ping pong ball) encounters a fissionable atom (mouse trap with ping pong ball) it induces fission and releases more neutrons (ping pong balls).

This video is the result of several hours of setting up traps and having them go off at all the wrong times.




Ideally the traps would be fixed to the surface so that only ping pong balls would set off other traps. As these traps went off not only did we record video but we also made a separate audio recording. It can be seen here plotted from the .wav file in Mathematica.

We next recorded one trap going off which was then plotted in the same manner. In theory the many mouse trap explosion could be recreated by taking linear combinations of the single mouse trap and overlapping as time goes by.

Using those two data sets and Mathematica's awesome computing skills we checked to see if we could plot the number of traps firing vs time. To do this we did a correlation between the two data sets to shows the degree to which the two data sets are linearly related. The plot below shows the amount of correlation (the number of traps firing) vs time.

As you can see the rate at which the traps are firing increases rapidly and then dies off. This is very different from a normal chemical reaction (A+B-->C+D where A and B are reactants and C and D are products) . The rate of a chemical reaction is proportional to the concentration of the reactants. The reaction is fastest the instant the chemicals are mixed and slows down over time because the reactants are consumed over time and their concentration falls. The fission reaction of can be written as follows A+B --> C+D+2A. Where A is a neutron, B is a fissionable atom, C and D are the products of the split atom B. So the reaction produces starting material exponentially. The reaction dies off because we are using up B.

So while we may just enjoy the demo because we like seeing ping pong balls fly across the room, there is so much more we can see in it. And that's what makes it a great demo.

Buttermilk Syrup

Before I started dating Marcelle she invited my friend and I over to have breakfast. She made waffles and buttermilk syrup. This is one of the best additions to breakfast since John and Will Kellogg started making cold cereal (and from me that's saying a lot!) After several large servings my friend suggested hooking the syrup up as an IV so that he could get it into his system faster. Not only is this syrup one of the most delicious confectionery concoctions (suitable to be eaten on just about anything), but it also is a great display of a multitude of kitchen chemistry phenomenon. I've now gotten ahead of myself, here is the recipe:

• 1 stick butter


• 1 cup sugar 1/2 cup buttermilk


• 1 tsp. vanilla


• pinch of salt


• 1 tsp. baking soda

Put the butter, sugar, salt, and buttermilk into your pan and just barely bring it to a boil. Take it off the heat and add the vanilla. While still warm and just before serving add the baking soda and stir, this will cause the syrup to foam and almost triple in volume (make sure there is room in your pan for this to happen). Now pour liberally over pancakes, waffles, and french toast. Also try it in combination with peanut butter and/or bananas, strawberries, and melon. Marcelle's favorite way to have it is on waffles with with fresh berries. The berries go in each little square and then you fill the rest of the square with the syrup. Yum!

Buttermilk syrup foams for the same reasons that baking soda and vinegar make fun volcano's, except the acetic acid has been replaced by lactic acid.

The first step is the protonation of the bicarbonate (HCO₃^- ) to form carbonic acid (H₂CO₃). Carbonic acid is in equilibrium with carbon dioxide and water as seen by the following reaction.

The equilibrium constant (k₁/k_-1)in this reaction explains why the CO₂ evolves rapidly. The rate constant for the forward reaction, k₁, is 23 s^-1. The rate constant for the reverse reaction, k_-1, is 0.039 s^-1. So the equilibrium constant (k₁/k_-1) in this reaction is ≈590 which lies heavily in favor of the products.

Now go and make your own kitchen chemistry marvel.

Liquid Nitrogen Pumpkin Ice Cream

Here is one of our latest kitchen chemistry adventures: Liquid Nitrogen Pumpkin Ice Cream. First the list of ingredients:

• 3/4 c. brown sugar


• 1 c. canned solid-pack unsweetened pumpkin


• 1 tsp. cinnamon


• 3 egg yolks


• 1/4 c. granulated sugar


• 1/4 tsp. grated nutmeg


• 1/8 tsp. ground cloves (this was a little too much for me)


• 1/2 tsp. ground ginger


• 2 c. heavy cream


• 2 c. milk


• 1/8 tsp. salt


• 1 tbsp. vanilla extract

Combine cream, milk, brown sugar and granulated sugar in a medium-sized saucepan over medium heat. Cook, stirring, until the mixture is hot but not boiling, about six minutes.

Whisk eggs in a medium bowl. Gradually whisk 1 c. of the warm cream mixture into the bowl with the eggs.

Pour the egg mixture back into the saucepan, reduce the heat to medium-low, and cook, stirring, until the mixture thickens enough to coat the back of a spoon, 5 to 10 minutes. Do not boil.

Strain the custard into another bowl and cover it partially with plastic wrap. Cool at least one hour at room temperature.

Combine pumpkin, vanilla, cinnamon, ginger, nutmeg, cloves and salt in a medium bowl and blend well. Add to the cooled custard and mix so that all the ingredients are evenly distributed. Refrigerate, covered completely, in the coldest part of your refrigerator until the mixture is very cold, about six hours.

Stir the cold pumpkin mixture, then pour into the mixing bowl of an ice cream maker. Freeze according to ice cream maker manufacturer's directions.

Put pumpkin ice cream in a container with a tight cover. Freeze at least three hours before serving.

Some helpful hints:

When thickening the custard so that it coats the back of a spoon (step 3), the temperature of the mixture should register at least 160 degrees F on a candy thermometer.

The refrigerated custard that has yet to be frozen in the ice cream maker (step 5) can stay covered in the refrigerator as long as three days.

The finished pumpkin ice cream tastes best if eaten within four days of making it.

When heating the custard in the thickening phase (step 3), do not boil it. The egg yolks will curdle.

Now for the cool part. Instead of making the ice cream in your ordinary every day ice cream maker we used N₂(l). Nitrogen makes up 78.1% of the air we breath and is completely harmless. When it is cooled to 77K (-195.79 °C, -320.42 °F) it becomes a liquid. We bought our N₂ from the chemistry department for $1 per liter. If you don't have a chemistry department handy you can purchase it from AirGas (my local store sells it for $2/L but you need a DOT approved container) Next we dumped the N₂ into the chilled custard and watched it harden into ice cream.

There are several videos of people doing this on YouTube so you can see how it's done. The Guinness Book of World Records says that the current record for making one L of ice cream is 18.78 seconds held by polymer physicist Peter Barham from the University of Bristol, UK.

Maybe I'll go for the record.