12. The Chemistry Of Epsom Salt - The History of Epsom Salts

When the virtues of Epsom Waters were first recorded chemical small analysis was in its infancy; magnesium as an element was not discovered until nearly a century later. Methods of measurement were not standardised, and there are some uncertainties in the conversion of the units quoted into their modern equivalents.

So Aubrey, the first to carry out some experiments with the water around 1654 (not published until 1719) reported that he evaporated about a gallon, which yielded "a sediment of flakey stuff, of the colour of Bay-Salt in loose flakes, as much as fill'd a Tobacco-Box". He gave it to old Dr. W. Harvey, "who thought it to be a sort of gray Nitre; but he spoke at random."

Later reporters became more accurate in their statements, and the table below is an endeavour to convert the chemical contents reported into modern units: grammes per litre.

We should realise (as contemporary observers noted) that the salt contents would vary not only with the amount of rainfall, but also with the depth of water at which the sample was taken.

Because Epsom water was no longer of importance in the 19th century, there are no comparisons of its magnesium sulphate contents with that of other spa waters, when these were meticulously analysed a century or so ago.

In spring 1989 the Borough of Epsom and Ewell arranged for a professional analysis of a sample of water taken from the old well. The result is included in the table below. It appears that the Epsom Salt contents are now much smaller than it apparently was in the 18th century.

Total Solids MgS04