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Box of litmus testing books used at Llwynypia Hospital.

Box is roughly size of matchstick box and has orange background with cream and brown labels. It slides open to reveal 6 tiny blue books of litmus testing strips, bound at he top with black tape.

Litmus is a water-soluble mixture of different dyes extracted from lichens, especially Roccella tinctoria. It is often absorbed onto filter paper to produce one of the oldest forms of pH indicator, used to test materials for acidity. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic (i.e. alkaline) conditions