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Darwin Correspondence Project

To Gardeners’ Chronicle and Agricultural Gazette   [before 6 March 1847]

Your correspondent “W. B. N”1 must, I think, have seen salt from other salinas than those described by me;2 probably (as I infer from his statement that the salt is brought into Buenos Ayres in ox-waggons), from the salinas north of S. Ventana. The salt from the Rio Negro, from the S. Chiquitas and from San Julian, instead of being an “amorphous mass,” yielding “a soft powder,” is coarsely crystallized, some of the cubes being even 3 or 4 inches square. Instead of being mixed with much earth, the salt presents an expanse as white as newly fallen snow, which, viewed from a distance, as I well remember to my cost, might readily be mistaken for a lake.3 Your correspondent seems to think that by the term purity, I imply freedom from dirt, but in my work I explain that I mean, “the absence of those other saline bodies found in all sea-water,”—a remarkable fact, which I state after the careful analysis of Mr. T. Reeks of the Museum of Econom. Geology.4 The salt consists entirely of chloride of sodium, with the exception of only 0.26 of sulphate of lime, and 0.22 of earthy matter. This fact having been ascertained, and the mass being well crystallised, it still appears to me that its lesser value for curing meat is probably owing to its purity, in the sense in which I have perhaps inappropriately used the term, that is, to the absence of those other saline substances found in sea-salt. I should not, however, have ventured on this opinion, had not Prof. Johnston5 come to the conclusion “that those salts answer best for preserving cheese which contain most of the deliquescent chlorides.”6 I must yet think that the experiment of adding some of the muriates of lime and magnesia to the salt from the Rio Negro, would be very well worth trial by the owners of the Saladeros near Buenos Ayres.7C. Darwin.


‘Native Patagonian salt’, Gardeners’ Chronicle and Agricultural Gazette, no. 8, 20 February 1847, p. 117.
Journal of researches 2d ed., pp. 65–7.
See Journal of researches 2d ed., p. 170. The incident occurred during an exhausting walk around the head of the harbour of Port St Julian, 9 January 1834.
For Trenham Reeks’s analysis of some of CD’s mineral specimens from the Beagle voyage see Correspondence vol. 3, letter to Trenham Reeks, [before 8 February 1845], and letter from Trenham Reeks, 8 February 1845.
James Finlay Weir Johnston, reader in chemistry and mineralogy at Durham University and the practical chemist of the Agricultural Chemical Association.
A paraphrase of comments printed in the Gardeners’ Chronicle and Agricultural Gazette, no. 6, 8 February 1845, p. 93, under the heading of ‘Report of the Agricultural Chemical Association’. See Journal of researches 2d ed., p. 66.
See Correspondence vol. 3, letter to John Lindley, [c. 10 October 1846], in which CD expressed the same opinion.


Corrects a misunderstanding of his description of salt deposits [in South America, pp. 74–5]. The salt referred to was from Rio Negro, and was coarsely crystallised and free of other saline substances found in sea-salt. CD believes its lesser value in curing meat is owing to the absence of muriates of lime and magnesia and suggests that it might be worth while to add them to the Rio Negro salt.

Letter details

Letter no.
Charles Robert Darwin
Gardeners’ Chronicle
Sent from
Source of text
Gardeners’ Chronicle and Agricultural Gazette, no. 10, 6 March 1847, pp. 157–8

Please cite as

Darwin Correspondence Project, “Letter no. 1069,” accessed on 19 July 2019,

Also published in The Correspondence of Charles Darwin, vol. 4