How dirty was a 17th century floor? Evidence from saltpetre diggers.

Today's Twitter extract from MEMSO reminds us of just how strange people's behaviour in the past can seem to us today.

The extract recounts the results of an examination of the behaviour of two saltpetre diggers (saltpetre being a key component of gunpowder). The men clearly had royal commission to seek saltpetre on private property, but were going beyond the bounds of decency in how they exercised their rights (see large copy of the report here). They were digging up the floors of churches, parlours, malting houses, dovecots, and even the private chambers of women 'in "childbed" (ie, in labour).

Why the men sought saltpetre in the (probably dirt) floors of private houses and buildings is not immediately clear, but a solution seems to appear in the facts relating to the historical manufacture of saltpetre.

Urine has also been used in the manufacture of saltpeter for gunpowder. In this process, stale urine placed in a container of straw hay is allowed to sour for many months, after which water is used to wash the resulting chemical salts from the straw. The process is completed by filtering the liquid through wood ashes and air-drying in the sun. (Wikipedia, extracted 30 April 2009)

The soil floors of the population's houses and barns were seemingly a rich source of both urine and straw, which also perhaps were allowed to build up over the months in a way which encouraged the crystalization process required for saltpetre.

A more detailed account of historical saltpetre manufacture can be found in an account of Joseph Leconte for the American military in 1862, which seems to confirm the process by which saltpetre built up naturally in the confined surroundings of the poor.

These conditions are often found in nature, as in the soil of all caves, but particularly those in limestone countries; and still more frequently under a concurrence of circumstances which, though not strictly natural, is at least accidental, so far as the formation of nitre is concerned, as in cellars, stables, manure-heaps, &c. In crowded cities, with narrow, dirty streets and lanes, the decomposing organic matter with which the soil is impregnated becomes gradually nitrified, oozes through, and dries on the walls and floor of the cellars, as a whitish crust, easily detectible as saltpetre by the taste.

If you know more about the history of salpetre, please post a message below.