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Darwin Correspondence Project

From H. C. Sorby   22 March 1876

Broomfield | Sheffield.

March 22/76

My dear Mr. Darwin

I am sorry you should have felt any kind of hesitation in writing to ask my help in any of your researches since at any time I shall be only too glad to do what I can to assist in any experiments that you may think it desirable to make.1 I only wish I could do more than I fear is possible in the case you name. Assuming that the sugar is glucose (i:e: grape sugar) the most delicate test I know is to take an ammoniacal solution of oxide of copper so dilute as to be only just a faint blue and to observe whether it is decolourized by boiling with the suspected substance. I really cannot say how small a quantity of glucose could be detected in this manner, but it must be a very small fraction of a grain—perhaps less than 1 100th. Perhaps other tests might be found but it would require considerable research to be sure. Even this is not a certain proof but if no decolourization occurred it would prove that glucose is absent or in very minute quantity. I do not know any very delicate test for cane sugar.2

In order to use the test one ought to have the leaves tolerably fresh and damp. If you like to send some I will try what I can do but will not promise that the results will be satisfactory.

All being well I must leave here for London on April 4th. so you ought to send the leaves as soon as you can.

I inclose a ticket for my conversazione. I should be delighted to see you at it but if you could not come, perhaps one of your sons could. I have therefore filled it up merely Mr. Darwin.3

Yours very truly | H. C. Sorby

I will send you a corrected copy of my address.4 Before you publish any thing on the subject, drop me a line, so that I may let you have the most recent results.


CD’s letter to Sorby has not been found.
The experiments were probably related to CD’s research on the conversion of starch to grape sugar by the digestive fluid of earthworms (see Earthworms, p. 37). Cane sugar: sucrose.
Sorby gave a conversazione to the fellows of the Microscopical Society at King’s College, London, on 21 April 1876. He exhibited a binocular spectroscope and illustrated his new method of measuring the position of bands in the spectra (Nature, 27 April 1876, p. 530).
Sorby had given the presidential address to the Royal Microscopical Society on 2 February 1876 (Sorby 1876; an annotated copy is in the Darwin Pamphlet Collection–CUL). On pp. 118–21, there was a discussion of CD’s theory of pangenesis.


Earthworms: The formation of vegetable mould through the action of worms: with observations on their habits. By Charles Darwin. London: John Murray. 1881.

Sorby, Henry Clifton. 1876. The president’s address. [Read 2 February 1876.] Monthly Microscopical Journal 15: 105–21.


Discusses chemical tests for the detection of glucose and cane-sugar in solution.

Letter details

Letter no.
Henry Clifton Sorby
Charles Robert Darwin
Sent from
Broomfield, Sheffield
Source of text
DAR 177: 218
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 10425,” accessed on 28 September 2021,

Also published in The Correspondence of Charles Darwin, vol. 24