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Darwin Correspondence Project

From J. H. Gilbert   9 March 1876

Harpenden | St. Albans

March 9, 1876

My Dear Sir,

In answer to your’s received today,1 I would suggest that you should not burn very raw lumpy clay, which would as you say give you something like brick, but a clayey soil not rich in manure, somewhat dry, & sifted, so as to offer much surface to the heat & to the air. The soil should be burnt until all coaly matter disappears, when, if of the same character as ours, it will have a brick red colour, but be porous and friable. I imagine the process could be very well managed on an iron plate over a fire as you propose, the soil being raked or stirred to renew the surface

As to washing the soil with acid, I think I would wash and draw off once or twice with water only; then add just enough acid (sulphuric) as to render the washings neutral or very slightly acid to test paper. then wash again with water; & finally roast again gently. I think I mentioned before that your manuring substances should be devoid of alkaline reaction.2

We shall be very glad to see your Son here in May or June.3 In the mean time we will make some observations on the plots as to variation, so far as we are able.

I am, My Dear Sir | Yours sincerely | J H Gilbert

To | Charles Darwin Esqre.

P.S. When I say that the manuring matters should not be alkaline, I mean that plants frequently suffer from that condition of things; but of course if in any case you could secure health with alkalinity of soil, you might get some varied tendencies thereby?


For CD’s questions regarding the preparation of soil containing no nutrients for his experiments, see letter to J. H. Gilbert, [before 9 March 1876] and n. 5.
CD had declined Gilbert’s invitation to visit the site of his experiments but said that his son Francis would go (letter to J. H. Gilbert, [before 9 March 1876] and n. 6).


Sends advice on preparing and washing soil in preparation for CD’s experiments.

Letter details

Letter no.
Joseph Henry Gilbert
Charles Robert Darwin
Sent from
Source of text
Rothamsted Research (GIL13)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 10416G,” accessed on 2 July 2020,

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