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Darwin Correspondence Project

To W. W. Baxter   4 September [1872?]1


Sept. 4th

Dear Sir

If you chance to have any of the following Salts I shd. be much obliged if you would send me 12 oz of each, as I want to try a little experiment with some plants.

Acetate of Ammonia

Citrate of Ammonia

Nitrate of Ammonia

Sulphate of Ammonia

Nitrate of Soda

Nitrate of Lime

I know that it is mere improbable chance whether you have any.

The Nitrate & Sulp. of Ammonia I care most about; Could you obtain them for me, as I do not know where to apply to for a small quantity, & I in fact only require a few grains.— Pray excuse my troubling you.—2

Dear Sir | Yours faithfully | C. Darwin.

P.S. ☜ | Please send 4 oz of Camphorated oil for friction of the abdomen.3


The year is conjectured from the likelihood that CD wanted chemicals for his work on Drosera and other insectivorous plants, which he resumed on 23 August 1872 (CD’s ‘Journal’ (Appendix II)). Baxter was CD’s usual chemist.
Reports of CD’s experiments on Drosera with these chemicals and others appear in Insectivorous plants, pp. 136–73. The purpose was ‘to show how powerfully the salts of ammonia act on the leaves of Drosera, and more especially to show what an extraordinary small quantity suffices to excite inflection’ (p. 136). He concluded that all the eight salts of ammonia caused the inflection of the tentacles, and often of the blade of the leaf, with the citrate being the least powerful and the phosphate by far the most (p. 168).
Camphorated oil was a mixture of camphor and olive oil (Milne 1869, pp. 47–9). It was used as a liniment to relieve pain and as a stimulant.


Insectivorous plants. By Charles Darwin. London: John Murray. 1875.

Milne, Alexander. 1869. Manual of materia medica and therapeutics, embracing all the medicines of the British pharmacopœia &c. &c. 2d edition. Edinburgh: E. & S. Livingstone.


Orders some salts for plant experiments.

Letter details

Letter no.
Charles Robert Darwin
William Walmisley Baxter
Sent from
Source of text
McGill University Library, Department of Rare Books
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 8510,” accessed on 25 October 2021,

Also published in The Correspondence of Charles Darwin, vol. 20