If you’ve been reading here for a while, you’ll know that one of my projects is to work with the Blists Hill museum to identify the contents of jars in its Victorian Pharmacy. This is a fairly slow process, mainly due to the constraints of other pressing tasks such as teaching, but it is a fascinating process. The pharmacy exhibit has a number (in excess of 300) of jars of pharmaceutical ingredients of some description, mostly labelled but some are not. Over the years some of the contents have been replaced with innocuous chemicals such as sugar, table salt and coloured water or oils. This process has not been documented and so no one really knows what is the real thing (as labelled) and what is a substitute.
Where do you start in this process? Well we started with a list of the labels on jars, then worked out which were full and which were empty. We set out to sample the jars over a period of time so that we could bring small quantities back to the lab to analyse. Some passed visual inspection, for example the copper sulfate looked like copper sulfate, others passed smell inspection such as oregano oil, but others give no clue to their identity by sight, smell or label. Where possible we start by comparing the substance to a modern day known sample. For example, we compared Pulv Rhei (rhubarb powder) to ground rhubarb (with sodium chloride to help break it down) and to oxalic acid by infra red spectroscopy. Yes, we put rhubarb on our ATR-IRs! (a specific type of infra red spectrometer) Or we compared the smell of rose water to a bottle of rose water swiped from my kitchen cupboard. If that doesn’t work, we try to figure out what it could be. In the case of Pulv. Rhei., the sample was a crystalline white solid, reminiscent of sugar or table salt. It was simple from there to perform a test to confirm the presence of sugar such as Benedict’s test or with Fehling’s solution. This can be verified by looking at the infrared spectrum, or grabbing a proton NMR (Nuclear Magnetic Resonance) for the high tech approach.
The potential inorganic substances provide a slightly greater challenge. Obvious things such as pH for suspected solutions of acid work quite nicely but don’t tell the whole story. Precipitation reactions provide an elegantly old fashioned way to tackle the identification. The sample of interest at the moment is Hydrarg Ammonat., which has been identified by colleagues as ammoniated mercury, and not something we would desire as a remedy these days. It was (and from a quick internet search, may still be), used as a remedy for skin complaints when formulated with petroleum jelly or similar. Now clearly the high tech identification technique would be some kind of trace metal analysis, and I could dissolve up the sample and put it through the ICP-OES (inductively coupled plasma-optical emission spectroscopy, determines type and concentration of metals). Instead, I’ve taken the more Victorian approach to the problem and gone for lo-tech precipitation reactions. The USP Monograph states a few tests that might be used to confirm the identity of ammoniated mercury (mercury (II) amidochoride:
– formation of yellow colour on heating with 1N sodium hydroxyde, ammonia gas evolved
– formation of red precipitate in warm acetic acid with potassium iodide added, residual solution forming white precipitate with silver nitrate.
Well it turns out that the sample turns red with potassium iodide which I presume to be the formation of HgI2 which is a similar reaction to the one in this video http://www.youtube.com/watch?v=pFovlKpPCbI.
As this sample is presumptive positive for mercury, I’ll be handling it with even more care and using the ICP-OES to confirm my ‘diagnosis’!