Mar 17th, 2015 — Chemistry

St. Patrick's Day - Green River Spectrometry

Talk about luck of the Irish! NSTA 2015 in Chicago happened to coincide with the city’s St. Patrick’s Day festivities and the greening of the Chicago River.

A group of us ventured to the river, with a PASCO Wireless Spectrometer in hand to try to get a spectrum and measure the “green” of the river.

Spectrometer at the green Chicago River

Getting a sample was not an easy task. Thankfully, no one seemed to notice or care when we rigged a collection device out of a plastic bag and a stick to scoop out some water.

Collecting a sample

We poured the sample into a beaker and were ready for testing!

Green river sample in a beaker

The water in the sample was surprisingly clear, considering how green the river looks. A real world application of Beer’s law! Absorbance depends on concentration combined with the path length - and there is a lot of river below us.

We pulled out the spectrometer, synced it to an iPad and recorded the spectrum.

Testing with the spectrometer

Again no one seemed to notice or care about what we were doing on the park bench. I assume it is because we looked like professionals, but it may have been the abundant amount of beer that was free-flowing (and also green for the festivities).

We brought the sample and spectrometer back for some comparison with some other samples. First we tested against water and a dilute solution of green food coloring.

Green river v green food coloring

The green river obviously had something in it, but it was not the green food dye.

After doing some research, it was suggested that fluorescein was once used to dye the river, but not any longer due to environmental concerns. Since we have a spectrometer and some fluorescein, we may as well test!

Fluoresceine and green river

Fluorescein, an orange powder, would make the river look green against a dark background, but our tests verifies that there isn’t any in the river sample.

The actual components use to dye the river are apparently a closely kept Chicago secret, known only to the leprechauns who do the coloring. Using the PASCO Wireless Spectrometer, we were able to verify what is not in the river, but the investigation to find out what it is continues. We will just have to go back to Chicago next year for some more testing!

Happy St. Patrick’s Day!

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