"put up curtains covered with lime"

Hydrated lime is an inorganic chemical compound of calcium hydroxide (Ca(OH)2). A white or colourless powder, it is formed by mixing calcium oxide (lime) with water. Mass-produced, cheap and easily handled, hydrated lime has a variety of uses. One of the most common is in water treatment or sewage plants, where it helps attract smaller particles and produces clearer water. It was also used as a disinfectant, especially in areas affected by diseases or where there was a high risk of infection from decomposing bodies (such as the trenches of World War I). Hanging the lime-soaked curtains would have been an attempt to protect the Members of Parliament from the feared cholera outbreak in London. Unprotected exposure, however, has its own health risks, including burning and lung damage, so today safer alternatives are used – not such a ‘wise’ idea as Catherine’s uncle observes.

Read more on the uses of lime in disinfection.