Dutched Chocolate

My sister recently asked me "Why is cocoa processed with alkali in so many chocolate flavored products?"

First what is alkali processing or dutching? A solution of alkali (a base), usually potassium carbonate, is added to the cocoa nib before roasting. It's also possible to dutch cocoa liqueur or powder. Most of the cocoa liqueur used for making cocoa powder is dutched but the majority of liqueur used for making chocolate is not. Alkalising was developed in the 19th century in the Netherlands by Coenraad Johannes van Houten1. He was trying to develop a chocolate powder that dissolved better in milk or water. Whether or not dutched cocoa dissolves better is still disputed but what the process definitely does do is change both the color and flavor of the cocoa.

The trick is to add just the right amount of base not too much because too much base will cause the triglycerides found in the cocoa butter to saponify thus giving it a soapy flavor. To avoid these off putting flavors small amounts of ethanoic or tartaric acid added to neutralize the high pH.

Some cocoa nibs are very acidic and the alkalising greatly helps flavor of the final chocolate product. Another thing that the base does is promote the formation of Miallard products (see another great article about how bases catalyze the Miallard reaction here.) Miallard products are those great flavors that form when proteins and sugar react.

The color change in the cocoa is due to reactions of the tannins in the cocoa. Tannins are polyhydroxyphenols, which means they are aromatic compounds (as apposed to an aroma compound) with several alcohol (-OH) groups. In the figure you can see a common one in cocoa, epicatechin. Depending on how the nib is fermented, dried, and roasted the tannins can join together, oxidize, and react with other chemicals in the cocoa to form color-giving molecules. This makes the cocoa much darker in color. By varying the pH, moisture content, and processing conditions it is possible to make cocoa of many different colors.

So when should you use alkali unprocessed cocoa? Well that depends on your leavening agent. Baking soda needs an acid to make it form CO2 and cause your cake to fluff up nicely. Adding acidic unprocessed cocoa will cause it to rise. Further more, baking soda is a base and if added to the already basic dutched cocoa it can cause the cocoa butter to saponify and give soapy flavors to the dish. But because baking powder is a mixture of an acid and baking soda you want to use dutched cocoa so that it doesn't taste too acidic.

1Casparus van Houten, Coenraad's dad, figured out how to easily remove cocoa butter from the nibs enabling the creation of cocoa powder. The nib contains about 54% cocoa butter by weight and this butter makes it difficult to mix into water or milk to make a drink. By pressing the beans, either with a hydraulic press or with a screw press, about half of the butter is expelled from the bean and the cocoa mass that is left can be ground into cocoa powder. This then allowed others to combine cocoa powder and sugar together and then remixing it with some of the cocoa butter thus forming something very close to the of chocolate of today.


DB Lavash and dips.

During this challenge Marcelle asked me to take a turn kneading the dough. A little while later, she gave me some constructive criticism on how I knead dough. It turns out that while I thought that I was kneading the dough, I was really just folding the dough in half and smashing it flat time and time again. What I was not doing was pulling and stretching the gluten molecules into a nicely aligned mass.

Harold McGee informed me that wheat flour is special in the grain family because it is the only grain whose endosperm proteins will interact strongly enough to form a gluten (most simply, a combination of gliadin and glutenin) that will support a raised bread. It is true that some other grains (like rye) will form gluten, but the formed gluten is weak and can't support the raising of the bread. To form a good bread the dough must be both plastic and elastic. Able to stretch out of shape when pressure is applied (plastic) and able to pull back to its original shape after the stress is removed (elastic). If the dough were just plastic, all of the carbon dioxide produced by those hard-working, fermenting yeasts would just flow to the surface and escape, making something very like bricks or hockey pucks. On the other hand, if the dough were completely elastic, the CO2 would be crammed into a few very pressurized pockets and the bread would come out looking like swiss cheese: a very dense mass with a few pressurized pockets of gas.

Unkneaded gluten is a coiled up protein that you can visualize like a Slinky. Unlike a slinky, the reason gluten stays coiled up is that there are chemical bonds (disulfide bonds) holding the spiral layers together. Kneading stretches the "gluten-Slinky" until those disulfide bonds break. Once stretched the disulfide bonds can reform with other broken disulfide bonds in the new stretched position to keep the gluten all aligned. After reading about kneading gluten doughs I realized that the disulfide breaking and forming is a lot like what is happening during a permanent wave, but this explanation will have to wait for another post. So even with my poor kneading technique the lavash was delicious, the dips were delightful (mostly), and best of all I learned some new chemistry.

I didn't find this project very challenging. My cracker experience is not vast, but I did make whole-wheat saltine/"wheat thin" type crackers once a week for our baby for about 8 months after he started eating solid foods and before I wanted to expose him to long-ingredient-list store-bought crackers. I have made a lot of pita bread--with a variety of outcomes and a ton (almost literally) of pizza dough, so flatbreads are not altogether foreign to me. The recent lavash challenge was fun and easy and made for a nice snack when we had some friends over to play games one evening.

I followed the instructions exactly, but I had a few problems; here they are, in no particular order. Despite using an oven thermometer and switching the lavash from top to bottom rack and front to back partway through baking, one pan was much darker brown than the other. The paler pan also made lavash that were puffed and chewy. I'm sure this has reference mostly to the cheap oven in our rental home, but other bakers I conferred with confirmed my experience. I used sea salt on one pan and poppy seeds on the other, but despite spraying water, 70% of them fell off before they were eaten.

For the toppings, we decided to try to the Tahitian almond spread recipe provided and also made a basic pico de gallo (tomatoes from our garden, onion, serrano chile, cilantro, salt). I also served some olivada (see Moosewood Restaurant Cooks at Home) I had made with green olives a few days before. The olivada is a long-time favorite and the pico disappeared quickly; when all the chunks had been dipped out of the bowl, the juices were very nearly drunk by our friend. The almond spread was a little weird. I love almond butter and eat it almost every day on toast for either breakfast or on an apple for a maternity snack, but putting it with garlic, cilantro, honey, orange juice and pine nuts did nothing to further endear me to a food I already enjoy as it is. I'm really looking forward to next month.


Daring Bakers

Marcelle and I have joined a great group called the Daring Bakers. Each month they send out a recipe that everyone is to follow and then on a given day everyone posts their results on the same day. August was our first month with the group and we made éclairs. We made a hazelnut cream filling with a chocolate toping. To quote our toddler son they were "DEElishush."

This, however, is a blog about science, so I want to talk about the science behind éclairs. The dough is very simple to make. First water, butter, and milk are brought to a boil, then flour is stirred in all at once. The dough that forms is stirred and cooked for a few minutes on the stove to swell the starch. Then you transfer the dough to a mixer bowl and eggs are beaten in, one at a time. The dough is piped onto cookie sheets and baked in a hot oven.

You notice that there is no chemical leavening agent included in the dough, such as yeast or baking soda, and yet it forms lots of wonderful air pockets during baking. How does this happen? Steam forms as the puffs bake and the strong gluten structure formed by beating the dough stretches to hold the steam. With the steam trapped, the heat then coagulates the gluten and egg proteins forming a rigid wall that will hold its shape. If done properly, the puffs will be golden brown, with a hollow center crisscrossed by a soft network of dough filaments.

Each ingredient plays a part in making a good puff. First the water, milk, and butter need to be boiling so that when the flour is added it will swell (hydrate) the starch granules and gluten (gluten is made up of two proteins gliadin and glutenin). The more butter you add, the more tender the cream puff will be, but if you have too much it will interfere with the gluten stretching and the cream puff will collapse.

The eggs that are beaten into the dough act as the leavening agent. The yolks add fat and act as an emulsifier for a smooth and even texture in the finished product. Egg proteins add to the structure of the cream puff as it cooks.

Baking any dough is a delicate dance between two processes: the expanding of gas and the coagulation of gluten and gelatinization of starch. If the oven temperature is too low, the trapped air will expand and escape before the gluten and starch have set. The puff will collapse and be a tough mass. Also, the puffs depend on steam production to cause the to rise: if the temperature is too low there won't be enough steam to cause the puff to rise, and if the temperature is too high, the proteins and starch will set and brown before the gas has expanded to its full size. This will again lead to unpuffed puffs.

This recipe was an exciting start to our membership in the Daring Bakers Club. I felt like many of the components were unnecessarily complicated--for example, the best glaze for eclairs I've ever tasted (and had great success with) is a simple 5/4 chocolate/cream ganache. It doesn't get any easier than making it in the microwave. The glaze recipe we were instructed to follow to the letter never set up, not even after time spent in the cool of our freezer for a while. It included silly component recipes (which tasted great as ice cream toppings) but did nothing to further our desire to repeat this recipe experience. The choux recipe chosen for us by this month's host was a good one, although many important instructions were omitted from the instructions--like how wide the puffs should have been in addition to how long, and whether they should cool on racks or on sheets or on parchment paper pulled off the sheets and placed on a counter/table. Dave complained that it seemed like this recipe was intended to dirty as many dishes as possible, and because he is our "dishwasher," he should know. We thought the double chocolate hit from the pastry cream and the glaze would be too much (even for confirmed chocolate lovers), so we opted for a hazelnut pastry cream that we created from our vast store of experience making hazelnut gelato and it turned out really nice. We WILL be making that part again. All in all, this was supposed to get us cooking together in the kitchen, which happened three nights in a row this week for us to get all our components together. So, in that way, despite my quibbling, it was an unqualified success! ---Dave's lab assistant


Chinese Chemistry

I really enjoy looking at the Periodic Table. I love the amount of information that is available in such a condensed form. I like the Table so much that I carry one in my wallet. There is one in the kitchen (in English) and one in the bathroom (in Spanish). As I was thinking about the periodic table I began to wonder what it looks like in Chinese. It just so happens that I work with a couple of Chinese guys so I asked them to show me a Chinese periodic table. I noticed right off that all of the Nobel gases had one shape in common throughout the family. Then I noticed that it wasn't just the Nobel gases but all of the gases had the same character. Then I noticed that the metals had another character and last the non-metal solids another character. My labmate explained that in Chinese the majority if the symbols are made up from two parts. The first part (the radical) tells you what the physical state of the element is at STP. The second part is phonetic and tells you how to pronounce the symbol.

I learned (after installing the East Asian languages on my computer) that there are four radicals used on the periodic table and they were the shapes I had noticed at the beginning. They are 金or 钅(literally "gold" for metal), 石 (literally "stone" for non-metal and metaloid solids), 水 or 氵 (literally "water" for liquids), and 气 (literally "air" for gases). The phonetic part is based on the western name of the element. Below you can see some examples of this radical phonetic symbol pairing.

Here "metal" and the phonetic "bi" combine to form bismuth.

"Metal" plus "nei" form "na" for natrium or sodium in English. I like this one because it shows that they aren't just using the English pronunciations of the elements.

"Stone" and "dian" form iodine.

"Air" combines with "fu" to make fluorine.

There is set class of symbols which are for elements that were known since ancient times. Elements which were known to the Chinese alchemists like gold, iron, sulfur, and mercury. I especially enjoy the symbols for iron and sulfur. Iron can be broken up into several parts.

Which could be interpreted "metal from the mountain for making weapons." Sulfur can be broken apart to show that it is a stone that flows.

Lastly there are some characters that are descriptive of the element that they represent. Examples are phosphorus and bromine. Phosphorous breaks down to "the stone that glows" and bromine is the "stinky liquid."

Some of the websites that I found especially useful are Zhongwen, a website about Chinese characters and their etymology, the Wikipedia entry on the chemical elements in East Asian languages, and an IUPAC article on the Chinese terms for chemical elements.



Two of the things I miss most from Ohio are fireflies and thunderstorms. I miss seeing the fireflies flashing out their seductive Morse code on a warm summer evening and I miss the ominous clouds, rushing wind, huge warm rain drops, flashing lightning and crashing thunder, and maybe most of all the smell right after a midsummer thunderstorm. So with these thoughts on my mind I decided to find out how a firefly produces light. I found some great cites and books to talk me through the process.

Lets first look at the structures. Shown below are firefly luciferin, luciferyl adenylate (luciferin attached to AMP), and oxyluciferin.

Another major player in the light emission from fireflies is the luciferase enzyme which mediates the entire set of reactions. The basic mechanism is as follows:
  1. Luciferin and ATP react to form luciferyl adenylate and inorganic phosphate (PPi)
  2. Luciferyl adenylate reacts with oxygen to form oxyluciferin*, CO2, and AMP (the * indicates an excited electronic state)
  3. The excited oxyluciferin* rapidly loses a photon of visible light as it goes to its electronic ground state.
  4. Ground state oxyluciferin is then regenerated into luciferin through a number of different steps.

This is summerized in the figure below.

For a more detailed explanation see Dr. Branchini's page on firefly bioluminescence, including information on the luciferase enzyme.


Periodic Table of Videos

This is a fun website put out by the University of Nottingham that tells a little bit about the elements on the periodic table. Some of my favorites are Na, P, He, and F.


Cogito Ergo Boom II

Last summer I heard about Summer Explosives Camp and I thought to myself what was I doing all those years at EFY? Then I learned that it hadn't been available when I was eligible and I felt a little better.

When I was at ISU I had an opportunity to go and see the research and development facilities at Thiokol. It was amazing. They talked to us about ammonium perchlorate (NH4ClO4) which is the oxidant that they use for the solid fuel rocket boosters. Because it is water soluble they need to be careful about getting it on their clothing because it will be soaked up and then it will dry in the clothing making the clothes very dangerous. To demonstrate they had a leather boot that they had soaked in a saturated solution for several days. They then allowed the boot to dry thus trapping all of the ammonium perchlorate in the leather. Next they lit the boot on fire starting at the toe. At first it didn't seem like much was happening and then a flame about 4 feet tall shot out of the leg of the boot and consumed the boot. After a few seconds all that was left was the steel toe of the boot. It was very impressive. They stressed to us that rocket fuel isn't explosive. You don't want an explosive fuel. You want a fuel that burns at a steady rate and extremely reproducible.

As we were entering a building they had us look out over the facilities and pointed out a two rows of buildings. They were evenly spaced identical buildings with one lot empty. Our guide told us that that was where a fire had broken out while they were mixing the fuel and the building was destroyed. At that point I decided that as cool as it would be to work with high energy materials, it was more important to come home every night.

So on to explosives. How can you predict how much energy will be released from a chemical explosion? That is a very difficult question and one that we still can't predict perfectly. There are a few rules of thumb that can get us to within about 10%-20% of the answer. The first step is to know the structure of the explosive. I've shown some common ones below.

Once you have the structures you can calculate the oxygen balance. When an explosion takes place the explosive molecule breaks apart into its individual atomic constituents. These quickly form several small stable molecules including H2O, CO2, N2, H2, CO, etc.

By considering the formulas of the explosives and determining how much oxygen is in the molecule compared with how much oxygen is needed to completely oxidize the fuel present. If there isn't enough oxygen it is called a negative oxygen balance, like TNT. If there is more oxygen than is needed it has a positive oxygen balance, like nitroglycerine.

There are tables that list the oxygen balance of different molecules and mixtures but it's easy to do even if you don't have a table. It's easy to determine the oxygen balance if you know the molecular formula.

When detonation of HMX takes place the explosive molecule is broken apart and oxidized to form gaseous products. To figure out the oxygen balance we need to assume that the explosive is completely oxidized to form carbon dioxide, water, and nitrogen.

C4H8N8O8 → xCO2 + yH2O + zN2

Now we need to balance equation. Let's start with the C,

C4H8N8O8 → 4CO2 + yH2O + zN2

next we do the H,

C4H8N8O8 → 4CO2 + 4H2O + zN2

now the N,

C4H8N8O8 → 4CO2 + 4H2O + 4N2

last the O. There are several ways to balance the oxygen but we are going to do it by subtracting O2 from the right side of the equation.

C4H8N8O8 → 4CO2 + 4H2O + 4N2 - 2O2

In order to balance the the formula we had to put a negative sign in front of the O2. That indicates a negative balance, meaning that it takes more oxygen than the HMX has to fully be oxidized to water and carbon dioxide.

This amount of oxygen as a weight percent of the total molecule can be calculated by taking the mass of the oxygen on the right side of the equation, -641 and dividing it by the molecular weight of HMX, 2962 all times 100%. (-64/296)∗100%=-21.6%.

The oxygen balance doesn't tell us the how much energy will be released from a given molecule or mixture but the strength, brisance, and sensitivity of an explosive or mixture are seem to increase as the oxygen balance approaches zero.

Zero oxygen balance also leads to fewer toxic gases released during the explosion. If the oxygen balance is negative CO is formed. If the oxygen balance is high NOx (NO + NO2) is formed. While this isn't a problem if detonating in open air with good ventilation, it is a problem in mines with poor ventilation.

So we haven't gotten to the part where we predict how much energy comes from a given explosive but this is enough for this post and the rest will just have to wait.

For more information on the chemistry of explosives see:

Akhavan, Jacqueline. The Chemistry of Explosives. RSC paperbacks. Cambridge, UK: Royal Society of Chemistry, 2004.
1. Take the molecular weight of O2 and multiply by the number of moles added to the right side = 32∗-2 = -64
2. 4C+8H+8N+8O = 4∗12+8∗1+8∗14+8∗16=296



Today I'll be talking about an important part of all combustion, oxygen. I decided to condense some oxygen and see what I could burn. To condense the oxygen I put a glass tube in some liquid nitrogen and started blowing oxygen into the tube. The boiling point of nitrogen is 77.36 K while the boiling point of oxygen is 90.2 K so the oxygen readily condenses in the glass. I then poured the lovely blue liquid oxygen onto some cotton and set it on fire. What you see below is what followed. Notice that there is no black charred cotton at the end.

Cotton is primarily cellulose so the chemical reaction for what is happening is:

(C6H10O5)n + n (6O2) --> n(6CO2 + 5H2O)

There is no leftover charred cotton because I had an excess of O2 the reaction went to completion turning all of the cotton into CO2.


Cogito Ergo Boom

I was walking home from school one day thinking about explosives and I overheard someone say cogito ergo sum. My brain interpreted this as Cogito Ergo Boom. I knew that I couldn't have been the first to come up with the phrase and I was right. But that won't stop me from using it.

For my next few posts I though that I'd talk a little about explosives. There are three main types of explosives: mechanical, chemical, and atomic. We'll start with mechanical explosives.

Mechanical explosions occur due to a physical change in the system. Examples of mechanical explosions are pipes freezing in the winter, dry ice bombs, popping balloons, and the heating of a whole egg in a microwave. In each of these pressure is built up in side of a closed system. Ice expands by about 10% in volume compared to the unfrozen water causing the pipes to burst.

The CO2 in the dry ice bomb goes from 1.5g/cm^3 to 0.044g/cm^3 at STP. So while the 40 grams of
dry ice that go into the 1 L bottle only take up 26 cm^3 once it all sublimes it will take up 224,000 cm^3 at STP.

While these are impressive displays of mechanical explosions the largest mechanical explosion to ever occur was the explosion of Krakatoa. The explosion of Krakatoa was equivalent to 200 megatons of TNT. For scale purposes the largest bomb that the US stockpiles is the Mk-B53 at 9 megatons. The bomb Little Boy, dropped on Hirosima, was about 13 kilotons or 13,000 times weaker than the explosion at Krakatoa. The largest bomb ever detonated was only 25% of Krakatoa. There are reports of people hearing the explosion over 3,000 miles away. It is the loudest sound in recorded history.

So while mechanical explosions are as easy to make as popping a balloon they are also the most powerful explosions know to man.


Temper Temper

To make chocolate look good, with a high gloss, and have a good snap it must be tempered. Tempering chocolate ensures that all the fat in the chocolate sets in the correct crystalline form.

To understand tempering we must first understand the structure of fat. The vast majority of the fats in chocolate are triglycerides. A triglyceride is a class of fats made up of glycerol linked to three fatty acids. Furthermore, three main fatty acids account for about 95% of the fat present. These three fatty acids are oleic acid (35%), stearic acid (34%), and palmitic acid (26%). Stearic and palmitic acid are saturated fatty acids, meaning all of the carbon atoms are saturated with hydrogen, while oleic acid is a monounsaturated fatty acid, there is one double bond which could be hydrogenated.
Fatty acids are called fatty acids because they have a long aliphatic carbon chain with an acidic carboxylic acid group at one end.

This diagram shows one of the ways these fatty acids are attached to the glycerol. Shown here is what is known as a SOP triglyceride because it has stearic acid attached to the first glycerol carbon, oleic acid in the middle, and palmitic acid in the third position. If we were to switch the oleic and stearic acids it would be a very different molecule.

As I said earlier stearic and palmitic acids are saturated while pleic acid is unsaturated. So our triglyceride is one of a subset of triglycerides found in cocoa butter known as SOS triglycerides. This set of triglycerides has oleic acid sandwiched in between two saturated triglycerides. SOS triglycerides make up 80% of the fat in cocoa butter. Because the fats in cocoa butter are primarily SOS triglycerides they melt over a short temperature range (room temp to body temp).

Cocoa butter is polymorphic which means that it can crystallize in multiple arrangements. Carbon is also polymorphic, it can be a diamond, graphite, or a bucky ball. While carbon has three polymorphs cocoa butter has six. These six forms were named by two different groups in the same year (1966). The chocolate industry uses Roman numerals I-VI as described by Willie and Lutton, while the oils and fats people prefer using Greek letters with superscripts and subscripts as set forth by Larsson (γ, α, β'2, β'1, β2, β1).

Form I (γ) melts from 61° to 67° F

Form II (α) melts from 70° to 72° F

Form III (β'2) melts from 78° to 80° F

Form IV (β'1) melts from 81° to 84° F

Form V (β2)melts from 93° to 95° F

Form VI (β1) melts above 97° F

Only one of these six polymorphs (form V) forms the shiny, firm chocolate that gives the nice snap when broken that we like. If we want to enrobe a truffle or a strawberry with chocolate and we want it to snap when we bite into it we need the chocolate to be in form V. Luckily chocolate comes from the factory in form V. If we can keep it there we will have lovely chocolates. Therefore our goal when we melt the chocolate is to never heat it above 91°-92° F.

Most chocolate melts between 89° -91° F even though all of the form V won't melt until you heat it above 95° F. Between 91° -95° F the chocolate still contains some form V microcrystals of cocoa butter. If you let the chocolate harden around these seed microcrystals it will all form form V chocolate.

If however you completely melt all of the precious form V crystals you need to start over by completely melting all of the chocolate. Be careful not to burn or separate the chocolate by heating it too high.

Next you should cool the chocolate rapidly to about 80° F and always use constant stirring. Cooling this low does allow some of the form III and IV crystals to form, but it gets a good start on the crystallization of the highly prized form V crystals. Now gently warm the chocolate to 86° F. This start the will start to melt the form III and IV so it should be held at this temperature for a few minutes, then warmed up to 91° to 92° F . This will finish melting all of the form III and IV crystals that were formed while cooling.

You can now test the chocolate to see if it is in temper by spreading a smear out on a piece of waxed paper, if it dries shiny and hard within 5 minutes your chocolate is tempered. Now that you have tempered chocolate you should eat it and enjoy. Just be careful about bloom (we'll get to that next time).


Seven Basic SI Units

There are seven basic SI units: the meter, second, ampere, kelvin, mole, candela, and kilogram. Of those seven only the kilogram is still defined by a man made object with no referent in nature. This means that in a vault outside of Paris there is a platinum and iridium cylinder (seen below nested in three glass jars) that cannot gain or lose mass. If you could get past security and cut off a small chunk it wouldn't have lost any mass at all. That's because it defines the kg. All masses are referenced to it. In 1889, 40 copies of this cylinder were made for national standards institutions around the world. These standards have all changed mass in different ways over the years; mass gain through dust accumulation or mass loss through cleaning. And although they can compare the copies with the original with an accuracy of better than 10-9 kg it is still not good enough because thy don't know how the standard has changed. This therefore has led to groups trying to define the kilogram with a universally verifiable standard.

Two major approaches are being followed: atom counting and electrical approaches. The atom counting approach is easy enough to understand-count every atom in a sample then multiply by the mass of the atom and then you have the mass of the entire sample. Unfortunately we can't do this yet. What we can do is grow very pure crystals. The leader in the atom counting field is the Avogadro Project. They are seeking to make a single crystal silicon sphere, using laser interferometry to measure the diameter and then because they know the crystal structure of silicon they can calculate the number of atoms in that sphere.

Why use silicon? Because technology has been developed to purify silicon to a higher purity than anything we can make. Silicon used in the semiconductor industry is >99.99999% pure. It is made through a multi-step process first with zone refining and then a single crystal boule is grown from pure molten silicon. The isotopic make-up is then measured with a mass spectrometer and average atomic mass is then calculated. This single cryastal is then cut and polished into a perfect sphere. Alright it isn't perfect but it is nigh-perfect. To quote Wikipedia:

On the Ø 93.6 mm sphere, an out-of-roundness of 35 nm (undulations of ±17.5 nm) is a fractional roundness (∆r/r) = 3.7 × 10–7. Scaled to the size of Earth, this is equivalent to a maximum deviation from sea level of only 2.4 meters. The roundness of that ACPO sphere is exceeded only by two of the four fused-quartz gyroscope rotors flown on Gravity Probe B, which were manufactured in the late 1990s and given their final figure at the W.W. Hansen Experimental Physics Lab at Stanford University.

The problems that they are facing are things like too much variation in the isotopes of the silicon and the thickness of the silicon oxide layer that grows on the sphere.

The second proposed method for redefining the kilogram is called the electronic kilogram. The idea is to design an incredibly sensitive balance that matches the weight of an object (the force exerted on an object by gravity) to an electromagnetic force produced by a coil of current carrying wire in a strong magnetic field. Then you could define the kg as 'the mass that can be suspended by the electromagnetic force generated when a specific amount of current flows.' So far the electronic kilogram has produced better results than the atom counting method, but it still can't provide an accuracy of a millionth of one percent every time.

1. Robinson, Andrew. The Story of Measurement. London: Thames & Hudson, 2007.


What does that number really mean?

I have found that in science we often use really big or really small numbers but we don't often relate that to something we intuitively know or have experienced. So I'm going to be putting out numbers and what they "really" mean.

I'll start by talking about how much energy the US uses. According to the Department of Energy's report on the Energy Consumption of the US in 2006 we used 99.8 quadrillion BTUs (or as the energy industry says "Quads") of energy. Our usage for the first 9 months of 2007 projected a usage of over 100 Quads by the end of the year. Let's first define our terms.

1 quadrillion = 1x1015

1 BTU = British Thermal Unit = energy needed to raise 1 pound of water 1 degree Fahrenheit.

So let's now see what we can do with these numbers. While we only get about 22.7% of our energy from coal (22.8 Quads) If you wanted to haul all of this coal in one train it would have 11 million cars and be 104,000 miles long. This train would be long enough to go around the world a little over 4 times. And that's just in one year.