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Darwin Correspondence Project

From Leonard Darwin   8 January 1878

Brompton Barracks, | Chatham.

Jan 8th. 1878

Dear Father

Today I tested that lamp black for ammonia.1 In doing this test, the substance is put into a still and the water that distills over is tested for the ammonia. A good deal of greasy matter came over, shewing the presence of oil or fat in the lamp black. The amount of ammonia present proved to be 0.1 to 0.2 per cent of the lamp-black. This is free ammonia, or ammonia in any salt. The test is not a very sure one, for some organic substances, of which urea is the only one I know of, test as if they were ammonia. But there is sure not to be more than .1 to .2 per cent of ammonia present. Carbon absorbs ammonia readily, and I think it would take up this amount, if the air near it had ever been charged with ammonia; as it is sure to be in a laboratory sometimes.

Your affec son | L. Darwin.


CD had asked Leonard to test lamp-black for substances injurious to growing plants; see letter from Leonard Darwin, 7 January 1878 and n. 1. See also Movement in plants, pp. 467–8.


Movement in plants: The power of movement in plants. By Charles Darwin. Assisted by Francis Darwin. London: John Murray. 1880.


Has been testing lamp-black for ammonia.

Letter details

Letter no.
Leonard Darwin
Charles Robert Darwin
Sent from
Brompton Barracks, Chatham
Source of text
DAR 186: 33
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 11317,” accessed on 19 September 2021,