Tomorrow is March 17th, and as they have done every St Patrick’s Day weekend for 52 years, members of Chicago’s Journeymen Plumbers Union have already set about the herculean task of dying their city’s eponymous river a brilliant shade of emerald.
The transformation pays tribute to all that Irish immigration has done for the city, an act of recognition unique to Chicago, and one that is sure to make expat Paddies the world over turn green with envy.
But the extraordinary effect is surprisingly easy to achieve. All it takes, say the journeyman plumbers, is 18 kg of vegetable dye to give nearly 3 million cubic metres of water the hue of a leaky fluorescent marker.
The nature of the dye has been a closely-guarded secret since 1966, when environmental activists urged the city to adopt what you might call a greener alternative to fluorescein, the dark orange chemical that had been used up until then.
Fluorescein, synthesised by the German chemist Adolf von Baeyer in 1871, is well known for what the linguists amongst you will already have guessed are its distinctive fluorescent properties. For reasons similar to those outlined by Keir in his earlier post about colour, molecules of the substance absorb blue light and re-emit it at lower energies, giving them a bright green appearance when dissolved in water.
This property made fluorescein a particularly useful addition to the uniforms worn by German Luftwaffe pilots during the Battle of Britain. Should their airplane be shot down (as nearly 2,000 of them eventually were), a small sachet of fluorescein pinned to the front of their lifevests would ensure that those landing at sea could be swiftly rescued.
This pioneering technique was soon adopted by the British, and by the end of the war their distinctive “Mae Wests” were also equipped with fluorescein dye packs, ready to be pulled open and turn the water green.
Since then, fluorescein has been widely used by city engineers to trace the flow of water and identify leaks in a complex system. It was in this way, according to legend, that the idea for greenifying the Chicago river first occurred to Stephen Bailey, a shameless self-publicist who filled the dual role of business manager of the Plumber’s Union and chairman of the St. Patrick’s Day parade.
So whether you choose to spend tomorrow downing green beer, donning the shamrock or kissing the Blarney Stone (a form of sham rock all its own), spare a thought for the lifesaving properties of fluorescein, and the wily Chicago plumber who ensured his own healthy little supply of green.
Gilead also turns green and thinks he might dye when dumped into water. He will be celebrating St Patrick’s Day on Twitter @gileadamit