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Darwin Correspondence Project

From Alfred Swaine Taylor to Edward Cresy1   10 December 1860

St James’s Terrace | Regents Park

Dec 10 1860

Dear Mr Cresy

I saw a passage in the Chemical News of Nov 24th,2 which I think will interest your friend Mr Darwin as to the recognition of saline matter in an almost infinitesimal state of division

At p 281 of that number (published by Mitchell Red Lion Court Fleet Street)3 you will find it stated that by a peculiar optical property 1/3000,000 of a milligramme (165th grain) of chloride of sodium or common table-salt may be discovered! This is equal to 1/195,000,000th of a grain!

A dilution to the extent of 1/500,000th grain admits of detection by the ordinary test,—nitrate of silver. The facts which you mention in your note regarding the Drosera serving to detect nitrogen by its sensitiveness, are very remarkable.4 The nitrogen in a salt of ammonia and the nitrogen in gun-cotton5 gutta percha—India rubber or Indigo are in very different states. It would be curious to try these substances—also ferrocyanide of potassium and ivory shavings

I am glad you think that Herapath has undergone a proper rasping in my paper6

I am | Your’s very truly | Alfred S Taylor

E Cresy Esqr

CD annotations

3.3 The nitrogen .  .  . potassium 3.6] scored pencil
End of letter: ‘Does not eating flies make Drosera so animalised— | Try whether Drosera plant contains much nitrogen. | Try with bit of zinc & silver or gold leaf, whether volume cited is potent?’7 ink


Taylor was the author of a book on poisons (Taylor 1848) about which Cresy and CD had been corresponding. See particularly the letter from Edward Cresy, 30 October 1860. Cresy subsequently sent Taylor’s letter to CD (see letter to Edward Cresy, 12 December [1860]).
The Chemical News 2 (1860): 281 reported the discovery of a new alkali metal (later called caesium or cesium) by Robert Wilhelm Eberhard Bunsen and Gustav Robert Kirchhoff with the aid of the new technique of spectrum analysis (see Bunsen and Kirchhoff 1860). The great advantage of this method, the report noted, was its extraordinary delicacy.
C. Mitchell and Co., founded by Charles Mitchell, published the two 1860 volumes of Chemical News; thereafter the journal was published by other companies.
CD had been experimenting on the effects of various salts of ammonia on Drosera leaves. His results were given in Insectivorous plants, chapter 7.
CD found that gun-cotton, a highly explosive, manufactured compound that consists of a series of nitrates of cellulose, was not digested by Drosera (Insectivorous plants, p. 125).
William Herapath, the Bristol medical chemist, was frequently on the opposing side of Taylor in medical jurisprudence cases, most notably in the notorious 1856 murder trial of William Palmer (the Rugeley poisoner). In 1860 Taylor issued a detailed paper demonstrating that the test for arsenic established by Edgar Hugo Emil Reinsch and much favoured by Herapath was inaccurate: the copper wire used in the test itself contained arsenic compounds. Taylor used this article to take issue with criticisms levelled at him by Herapath in a letter to the Lancet (1859 (2)): 248. (Taylor 1860, pp. 219–20 and 220 n. 1). See also Coley 1991.
CD’s note refers to the statement in the letter that a dilution of common salt to the extent of 1/500,000 of a grain can be detected by nitrate of silver. In Insectivorous plants, pp. 174–88, he gave the results of testing the response of Drosera leaves to very dilute solutions of various salts. His manuscript notes are in DAR 54, 60.1, and 60.2.


CD may be interested in a reference to a method of detecting 1/195000 of a grain of sodium chloride.

Also, on Drosera, suggests it would be interesting to try substances such as gun-cotton, in which nitrogen is in very different states from a salt of ammonia.

Letter details

Letter no.
Alfred Swaine Taylor
Edward Cresy
Sent from
London, Regents Park
Source of text
DAR 58.1: 14–15
Physical description
4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 3015,” accessed on 21 May 2018,

Also published in The Correspondence of Charles Darwin, vol. 8