Today has been quite an interesting day - I've spent the morning with 10 very smart A-level chemistry students (that's second to last year of high school in non-England school systems). We were analysing the contents of jars in a pharmacy exhibit. It turned out to be a real life 'what am I?' but instead of being confronted by several chemical structures and working out what the household item was, we were confronted by 14 samples of solids and liquids with labels that did not make much sense. Do you know what pulv rhei is? No, we didn't either this morning.
Lets backtrack a wee bit and explain. Ironbridge Gorge is a World Heritage Site not too far from Keele. Amongst the wonderful museums there is Blists Hill Victorian Town which is a village sized museum where you can visit Victorian style shops and buy things, either with modern money, or you can change your money for olde worlde money. One of the shops is a pharmacy that was recently used as part of the set for a BBC TV series 'The Victorian Pharmacy'.
It looks pretty typical for a museum version of a Victorian Pharmacy with one exception - most museums just have empty, clean jars. This one doesn't - about 300 of the jars along the back shelves are filled with substances that may or maynot be those detailed on the label. The museum got in touch with one of my colleagues last year about the potential safety issues surrounding unknown chemicals - what if they were spilled? What action should be taken? We agreed to carry out an assessment of the chemicals and try to identify as many as possible. On one level, that involves looking up the labels on the internet or in various Pharmacopoeia and working out that Pulv Rhei may well be powdered (pulverised) rhubarb. On another level that involves a series of wet and analytical chemistry techniques to determine if the contents are what they say they are. Over recent years, various curators of this collection have made substitutions of the jar contents, replacing substances like boric acid with salt or sugar. Unfortunately little documentation has been carried out so we're trying to change that. A few weeks ago a group of students went with my colleague and did some testing on site, and started the task of sampling the jars. Today the A-level students came up to use our chemistry labs to analyse the contents.
Why are we using school children for this task? Actually, analysing these unknowns is good fun and an excellent open ended experiment. We thought it would make an excellent outreach activity, making a good contribution to the project. Today we provided the students with a sample each and let them come up with a plan for analysis. We offered them various wet chemical techniques such as flame tests to identify metals like copper, pH tests to confirm acid or base, reaction with acid to generate CO2 gas (turns lime water cloudy) if we thought it was a carbonate. We also let them use our infrared and NMR spectrometers to further analyse samples. We also provided known, modern versions of chemicals where we could identify them. The students really enjoyed the problem solving type activity although the biggest criticism was that we couldn't tell them for definite at the end if their answer was correct or not.
And what of Pulv Rhei? We provided a stalk of rhubarb for comparison and the student pulverised that with table salt before running an infrared spectrum. That showed a lot of water. The actual sample was a crystalline white powder so we suspected it might by oxalic acid, a chemical known to be in rhubarb, particularly the leaves. We ran the IR of the original sample and the oxalic acid but it wasn't that either. Searching the IR library indicated some similarities with the spectrum of sucrose. A simple wet chemical test using Benedict's reagent confirmed the presence of a sugar.
We analysed 14 different samples this morning and managed to work out about 10 of them. Many weren't what they said on the label. Some samples had deteriorated with age (potassium permanganate for example), others had been substituted for new unknowns. That leaves us about 200+ samples still to do, but fortunately the school are eager to come back to analyse more in June, and we have a couple of other school groups interested in the project. The real question is which of us is volunteering to take the compounds in the poison cupboard for analysis! I suspect that may be my job for July.