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Darwin Correspondence Project

From J. H. Gilbert to Francis Darwin   10 June 1876

Harpenden, St. Albans

June 10, 1876

My Dear Sir,

It is difficult to form a decisive opinion upon the “Natural” & “burnt” soils from the data recorded.1 Dr. Frankland does not state the method of analysis adopted, but from his expression that it cannot be concluded from the results that the constituents “are at present in such a form as to be capable of assimilation by plants”, and also from the results themselves, I gather that the quantities of lime, magnesia, potass, Soda, and phosphoric acid, are those yielded to extraction by acid; and in that case the quantities at present available will certainly be very much less than those represented by the figures, but how much less it is difficult to conjecture. Nor do you say whether, after the first burning, you extracted the mass by water, & then re-burnt? If you did and washed until the water came off pretty pure, and without marked alkaline reaction to test paper, I imagine you may assume your burnt soil to be a poor enough matrix for your purpose.

I enclose for your information a summary of many published results of analyses of soils; and also some comparative results on unburnt & burnt soils by Dr. Voelcker.2 From the former you will see that the amount of the important constituents yielded up to acid is generally very much greater than in your burnt soil (supposing it to be so analysed). Dr. Voelcker’s burnt soils also show much more of such constituents than your’s. The amounts of Lime, Magnesia, and potass in your burnt soil are, however, somewhat large if in an available condition, and in the burnt soil they would probably be more so than in the unburnt. Still, if you washed the burnt soil, and Dr. Frankland’s analyses represent the quantities taken up by acid, I am disposed to think you will have it in a sufficiently poor matrix.

If you care to see our experiments on the mixed herbage of grassland, and other field experiments, this is a very good time, & you should certainly come within a fortnight from the present time. I shall be in London from Wednesday evening to friday morning next, but know of no other engagement within that period, & shall be very glad to see you any day by previous appointment. You can leave St. Pancras (Midland) at 10.35 for Harpenden Station.3

I am, Yours sincerely | J. H. Gilbert

Of course we should be delighted to see your father also, if he can bear the fatigue—and if he come we should hope to see you in the afternoon for dinner & the night so as to be rested before seeing the experiments. If you come first you can judge how far it would interest your father

To Francis Darwin Esqre | Down, Beckenham, Kent


See letter from Francis Darwin to J. H. Gilbert, 8 June 1876. CD was interested in growing plants in soil from which the nutrients they usually absorbed had been removed, so that he could control the nutrients they were given and assess the effect different nutrients had on variation (see letter to J. H. Gilbert, 16 February 1876). Francis and CD had burnt and washed soil following Gilbert’s instructions and had sent samples of burnt and unburnt soil to Edward Frankland for analysis (letter to Edward Frankland, 6 June [1876]). The experiments were later abandoned (LL 3: 342).
The summary and Augustus Voelcker’s results have not been found in the Darwin Archive–CUL. For an article by Voelcker on the effects of burning soils, see Voelcker [1875], ‘On paring and burning’.
There is an undated letter at Rothamsted Research (archives of the Lawes Agricultural Trust, Rothamsted, Harpenden) from Francis Darwin to Gilbert declining this invitation owing to pressure of work.


LL: The life and letters of Charles Darwin, including an autobiographical chapter. Edited by Francis Darwin. 3 vols. London: John Murray. 1887–8.

Voelcker, August. [1875.] Contributions to agricultural chemistry. 2 vols. London: n.p.


On burnt soils.

Letter details

Letter no.
Joseph Henry Gilbert
Francis Darwin
Sent from
Harpenden, St Albans
Source of text
Rothamsted Research (GIL13)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 10535G,” accessed on 29 January 2022,

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