Kitchen chemistry: esters

Our previous kitchen chemistry post discussed acids, particularly the acetic acid in vinegar (and its reaction with sodium bicarbonate):

Acids like acetic acid, with a structure that looks like X–COOH, are also important because they react with alcohols (with a structure Y–OH) to form compounds called esters. The reaction is X–COOH + Y–OH → X–COO–Y + H2O. For example:

Esterification reaction

Industrially, strong acids are often used to make this reaction happen, but biologically, enzymes do the job. The combination of acetic acid and ethanol is ethyl acetate (used in some nail polish removers), and the image below also shows isoamyl acetate and geranyl acetate. Each ester has the same X–COO–Y structure:

Various esters

Esters have a “fruity” smell, and indeed the odour of fruit is largely a result of a mix of various esters (go on, sniff some fruit, and celebrate the complex odours that you smell!). Synthetic fruit flavours likewise use esters, but typically in a simpler mix that never smells quite like the real thing.

      

James Kennedy has produced this wonderful infographic of esters and their smells (click on the thumbnail to zoom):

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Carbon dating: Science in the service of History

In 1949, Willard Libby proposed carbon dating, a method for dating carbon-containing objects (like wood, leather, or cloth) that exploits the radioactive decay of carbon-14. The diagram above [redrawn from J. R. Arnold & W. F. Libby, “Age Determinations by Radiocarbon Content: Checks with Samples of Known Age,” Science 110 (2869), 678–680, 23 Dec 1949] shows the decay curve for carbon-14, together with some comparison samples Libby used (including wood dated by tree rings and items from the tomb of Pharaoh Zoser, for whom the first of the pyramids was built). It’s a very good fit! Later tests of carbon-dating have used dendrochronology back to about 10,000 BC.

The carbon in plants contains about one part per trillion of carbon-14, which the plants absorb from the atmosphere. The same amount of carbon-14 is present in animals, which get their carbon by eating plants or other animals. All living things therefore contain about one part per trillion of carbon-14. In dead plants or animals, however, the carbon-14 decays with a half-life of 5,730 years. For practical dating purposes, measurements of carbon-14 are adjusted to match the tree-ring data, so as to compensate for small changes in the amount of atmospheric carbon-14 over time. Such calibrated dates are reported as “Before Present” (BP), where “Present” means 1 January 1950.

One of the most famous examples of carbon-dating has been the Shroud of Turin, purported to be the burial shroud of Jesus Christ, and shown below in a negative image from 1898. The Shroud has been carbon-dated to between 1260 and 1390 AD, which is consistent with its denunciation as a forgery by the Bishop of Troyes in 1389, shortly after it first appeared on the historical scene. For the dating story, see P. E. Damon et al., “Radiocarbon Dating of the Shroud of Turin,” Nature 337 (6208), 611–615, 16 Feb 1989.

Fourteen fantastic visualisations, ancient and modern

A recent post in Wired highlights “14 world-changing data visualizations from the last 4 centuries.” Definitely worth a look!

The NASA map of ocean currents above is on the list, as are the classic epidemiological visualisations below, by Florence Nightingale and John Snow (the NASA map is also available as a video).

    

Oscar Dresses over the years

The wonderful infographic above shows the Oscar dresses worn by “Best Actress” winners from 1929 onwards (click to zoom). This infographic, by Mediarun Digital, has made its way across the Internet.

My graph below (again, click to zoom) extracts the major colour of each of those dresses, on a plot with saturation as the vertical axis. A general trend to brighter colours is noticeable, against a backdrop of black, grey, and white.

1957–58, the International Geophysical Year

The International Geophysical Year (actually a year and a half, from July 1957 to December 1958) saw the beginning of the “space race,” and the collection of a huge amount of valuable data. The science books I grew up with as a child were constantly referring to the results of the event.

The IGY, as it was abbreviated, included several solar eclipses (23 Oct 57, 19 Apr 58, 12 Oct 58) as well as the record-breaking solar maximum of 1957/58. In fact, February 11, 1958 turned out to be a very good night for Aurora chasers.

The IGY incorporated, among other activities:

    

Perhaps the world can use more collaborative efforts like the IGY.