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Inventory no. 41667 - Former Display Label #2


The damp walls of this basement have a tendency to exude nitre or saltpetre (mainly potassium and calcium nitrates - see the adjacent label), formed by the decomposition of organic waste material in the old 'Town Ditch' and from Exeter College's 'privy house' (established in 1612), the contents of which collapsed into the site during the digging of the foundations. The first attempt at a systematic analysis was by Martin Wall, MD, FRS (1747-1824), Reader in Chemistry in the University of Oxford, whose paper on the subject was read before the Manchester Literary and Philosophical Society on 19 November 1783. Dr Wall wrote:

"A common and familiar fact ... will at least prove, that if nitre ... is not obtainable from the putrefaction of animal matters only, the addition of a very small quantity of vegetable matter is sufficient for its production. I argue from the quality of the saline efflorescence found on old walls, which are exposed to impregnation from animal matters in a state of putrefaction. The wall of one end of my chemical school, or laboratory, is almost entirely covered with such an efflorescence. The laboratory is a large vaulted room under ground, into which the sun seldom has admission. It is built of stone, and therefore, except when fires are kept up for lectures, or occasional experiments, is liable to be damp. The wall, to which I allude, is immediately under a retired passage, a very convenient place of retreat to foot-passengers under certain circumstances of necessity. The ground, therefore, and the adjacent wall have been for years largely impregnated with excrementitious animal fluids, in all the different stages of putrefaction. The saline efflorescence on such walls is sometimes supposed to be alkaline, and really to be the fossile alkali; but ... in this instance, with which others of a similar sort probably have some analogy, it was perfect nitre".
M Wall, ""Remarks on the Origin of the Vegetable Fixed Alkali, with some collateral Observations on Nitre"", Memoirs of the Literary and Philosophical Society of Manchester, vol. 2 (1785), pp. 77-78 (pp. 67-79).

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