February 25 marks the passing of Theodore H. E. Svedberg. Svedberg was a Swedish chemist best known for the invention of the ultracentrifuge.
Svedberg was a colloid chemist studying the various physical properties of particles suspended in solution such as diffusion, light absorption, and sedimentation. His work helped prove Einstein’s theory of Brownian motion applied to particles in a colloid and gave the first physical evidence of the existence of molecules. In order to accomplish this, Svedberg needed to separate his colloids.
Colloids are insoluble mixtures suspended in some other substance. Left to their own devices, many colloids will settle into layers with the heavier particles at the bottom and lighter floating on top thanks to gravity. Think of a bottle of oily salad dressing. Shake it up, herbs are distributed evenly throughout the dressing container in the oil. Let it sit for a while, you’ll find the herbs on the bottom and the oil sitting on top. The problem is the amount of time this process takes. Gravity alone is not enough to quickly separate a colloid.
The most common method of helping gravity along is the centrifuge. A centrifuge is basically a quickly spinning wheel that uses centrifugal forces to increase the forces acting on the particles in solution. The faster the wheel spins, the more force it generates. Problems arise when the centrifuge is spinning too quickly. It is relatively easy to make a centrifuge rotate hundreds of times a second, but an unbalanced load would cause the machine to shake apart. Balancing the load helped, but when the rotation is ramped up, the air around the machine heats up and swishes around just like a fan and adds its own unbalance.
Svedberg found if he added a refrigeration system and encased the spinning parts in a low-pressure hydrogen atmosphere, these problems were greatly reduced. In fact, his system could be ramped up from hundreds of revolutions per second to 40,000 revolutions per second. This amounted to subjecting his samples to forces in excess of one million times the force of gravity. This was fast enough to separate biological macromolecules such as proteins out of solution. Svedberg used this to determine the molecular weight of hemoglobin in blood and casein in milk. His ultracentrifuge earned him the 1926 Nobel Prize in Chemistry and has become an important piece of laboratory equipment for biologists and polymer chemists.
Svedberg is also a non-SI unit of time. It is applied to sedimentation rates or how fast a particle settles to the bottom of a test tube in a centrifuge. How quick is a svedberg? One svedberg is defined to be 10-13 second.
Notable Science History Events for February 25
1999 – Glenn T. Seaborg died.
Seaborg was an American chemist who discovered ten of the transuranium elements and over 100 different isotopes. These elements were plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium and element 106. Element 106 was named seaborgium in 1997 in his honor. He shares the 1951 Nobel Prize in Chemistry with Edwin McMillan for these discoveries.
Seaborg also proposed the actinide group arrangement for the periodic table.
Fun fact: Seaborg managed to obtain a patent for two elements: curium and americium.
1971 – Theodor H.E. Svedberg died.
1953 – Sergey Nikolayevich Winogradsky died.
Winogradsky was a Russian microbiologist who pioneered modern bacteriology and discovered the process of nitrification of soil by bacteria. He also identified how sulfur bacteria obtain energy from the conversion of hydrogen sulfide to sulfur and then sulfuric acid.
1950 – George Richards Minot died.
Minot was an American physician who shares the 1934 Nobel Prize in Medicine with George Whipple and William Murphy for their research into anemia and liver therapy. Whipple had shown that pernicious anemia in dogs could be treated by feeding them raw liver. Minot prepared liver extracts that became the primary treatment for human anemia until the vital compound in liver was identified as vitamin B12.
1909 – Lev Andreevich Artsimovich was born.
Artsimovich was a Russian nuclear physicist who invented the Tokamak reactor to study controlled fusion. The Tokamak reactor confines plasma into a small donut shaped area using magnetic fields while being heated until fusion takes place.
1896 – Ida (Tacke) Noddack was born.
Noddack was a German chemist who, with her husband Walter, discovered the element rhenium. Rhenium was the second to last naturally occurring stable element discovered. It was isolated from platinum ore and the mineral columbite. The group announced they had found the element technetium when they bombarded columbite with electrons, but their results were never verified. They named their discovery masurium after the Masuria in Eastern Prussia.
1869 – Phoebus Levene was born.
Levene was a Russian-American biochemist who discovered nucleic acids came in two different forms called DNA and RNA based on ribose and deoxyribose. He identified the components of DNA where it contained adenine, guanine, thymine, cytosine, deoxyribose and a phosphate group. He also determined these components linked together as phosphate-sugar-base units he called nucleotides. He believed the structure of DNA was based on a tetranucleotide where the different components were equally distributed.
1723 – Christopher Wren died.
Wren was an English astronomer and architect. After the Great Fire of 1666, when London was essentially burned to the ground, Wren presented plans to rebuild the city. Before his death, he designed and built over 50 churches, including St. Paul’s Cathedral as well as many other buildings. He was also one of the founding members of the Royal Society.