February 12^th marks the passing of Dirk Coster. Coster was a Dutch physicist who co-discovered the element hafnium with George Charles von Hevesy.

For many years, element 72 was a missing spot in the periodic table. Several chemists searched for the element in zirconium minerals since many of these minerals had unknown impurities. Since the mid-1800s, many believed they had found element 72 in these minerals and an assortment of names were proposed. Swedish chemist Lars Svanberg reported his find as norium. Henry Clifton Sorby observed a new spectral line in zirconium and named his discovery jargonium, but retracted his claim the following year due to experimental error. Tellef Dahl believed he had discovered Norwegium. Other claims of ostranium, nigrium, euxenium were announced. French chemist Georges Urbain announced he had isolated element 72 from a rare-earth sample and named it celtium. Russian chemist Nenadkevich thought he had isolated thorium in the mineral orthite, but it had a much lower atomic weight, one that would correspond to element 72. He named his discovery asium, but could not publish his find due to World War I and the Russian Civil War.

Coster and Hevesy would find their element 72 in a zircon mineral by x-ray spectroscopy. They had been working in Neils Bohr's laboratory when Bohr won his Nobel Prize. Coster notified Bohr of the discovery and wanted to name it hafnium, after the Latin name of Copenhagen. Bohr wanted to name it danium, but he accepted Coster's name. Bohr amended his Nobel lecture to include the announcement of the discovery.

Hafnium has a very busy history. Find out what else occurred on this day in science history.

I've been adding to my coverage of alchemy bit by bit and came across an alchemy/chemistry project over at The Alchemy Website that you might enjoy trying. It is making purple gold. Colored gold alloys are seen in jewelry and gold is often added to glass to give it color (e.g., ruby glass), but this project is a little different. You'll be performing any of a number of chemical reactions to make a gold chloride solution turn purple.

What You Do

• Mix together a dilute gold chloride solution (0.01%) and a 1% Rochelle salt (potassium sodium tartrate) solution. It's best if you use distilled water to prepare your solutions, as contaminants in tap water may affect your results.

• Another option is to make "Purple of Cassius". This is a purple gold made by introducing tin to a very dilute gold solution. The author of the article posted at The Alchemy Website attempted to produce this color by reacting a dilute solution of gold chloride with stannous chloride. He obtained an amber solution, but not the desired purple coloration.

• Gold may be reduced using formaldehyde. Add some sodium bicarbonate to a gold chloride solution to make the solution alkaline before introducing a drop of formalin.

• Another recipe calls for add a few milliliters of gold chloride to boiling water and then adding some 1% tri-sodium citrate and boiling the solution until the desired color is produced. This colloidal solution is best kept in a shady location, as it is said to be photoreactive.

• In general, gold chloride solution is photoreactive, so you could soak a filter paper with the solution and expose it to sunlight to seek a color change.

Alchemy is an experimental venture, so if you're interested in making purple gold, get out there and try some projects. Keep good notes and if you see good (or otherwise interesting) results, post specific instructions for other inquisitive people to try.

February 11^th is Josiah Gibbs' birthday. Gibbs was an American chemist who didn't get much recognition for his work until after his death. He began his career with an engineering degree tutoring Latin and Natural Philosophy at Yale. After a tour in European laboratories for three years, he found a new love in chemistry and physics. He returned to Yale and was appointed their first Professor of Mathematical Physics.

He worked on a variety of projects including the development of vector analysis as a mathematical tool, optics and statistical mechanics. His largest contribution was combining the study of thermodynamics and chemistry. He introduced the concept of chemical potential and free energy. This was a concept that related all the different energies such as chemical, electrical, and thermal and the entropy of the system and the system's ability to perform mechanical work.

Gibbs laid the groundwork for mathematical physical chemistry and chemical thermodynamics. Find out what else occurred on this day in science history.

The periodic table organizes the chemical elements according to increasing atomic number, grouped by recurring or periodic properties. All periodic tables include the symbol, atomic number and atomic weight for each element. Some tables also include photographs of the elements. The truly amazing tables are the ones that include real specimens of the elements, so you experience them firsthand. Have you ever seen a "real" periodic table like this? One such table may be found at the Houston Museum of Natural Science. The table marks the entrance to the Welch Chemistry Hall at the museum. It showcases many of the elements, plus you can gain additional facts about the elements and chemistry.

Do you know of other locations that offer a real periodic table? If so, be sure to post a response.

Photo: Snapshot of a portion of the periodic table at the Houston Museum of Natural Science. (Anne Helmenstine)