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To Edward Frankland   18 October [1873]1

Down, | Beckenham, Kent.

Oct 18th

My dear Sir

Once again I have to thank you for all the trouble which I have caused you. It was my simple ignorance: I had always heard of & seen blue litmus paper, & could not believe that it was right.—2

Yours truly obliged | Ch. Darwin

1
The year is established by the relationship between this letter and the letter from Edward Frankland, 16 October 1873.
2
CD had received some sensitive litmus paper from Frankland, and had queried whether it should be pink, or whether it had been exposed to acid in the post (see letter from Edward Frankland, 16 October 1873 and n. 1). Litmus paper is purple when in a neutral environment.

Please cite as “DCP-LETT-9100A,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-9100A