From August Wilhelm von Hofmann   27 June 1862

R. College of Chemistry

June. 27. 1862.

My dear Sir

I have to apologize for transmitting to you only now the specimens of Carbonate of Ammonia and Gelatine, which I had promised to you.1 I have examined both; they are free from chlorine and may be used for your experiment.2 It was not quite easy to get a sample of gelatine without chlorine; a very considerable number of specimens, which I tested contained abundance of this element. In fact hydrochloric acid is the agent by which gelatine is generally separated from the earthy phosphates. At last I procured a sample from the french exhibition which I found to be pure and which I forward to you.3

Hoping that the chemicals may not arrive too late for your experiment, I remain | My dear Sir | Yours very sincerely | A W Hofmann

The Specimens are sent in a box forwarded by Rail

1
No letter from Hofmann containing this promise has been found. Hofmann was the director of the Royal College of Chemistry; in 1860, when CD was investigating the sensitivity of the hairs of Drosera, an insectivorous plant, to certain chemical substances, Hofmann provided CD with information about the sensitivity of chemical tests (see Correspondence vol. 8, letters from A. W. von Hofmann to Edward Cresy, 13 October 1860 and 27 October 1860, and letters to Edward Cresy, 14 October [1860] and 2 November [1860]).
2
CD had become interested in the sensitivity of insectivorous plants to different chemical substances in the summer of 1860, and had continued to experiment on the subject (see Correspondence vols. 8 and 9); the results of this research were ultimately published in Insectivorous plants. He had recently carried out experiments to determine the effects of carbonate of ammonia on Saxifraga platypetala (a synonym of S. hypnoides, mossy saxifrage) (see the experimental note in DAR 54: 27, dated 22 April 1862) and on Drosera (see the note in DAR 54: 75, dated 21 May 1862). The effects of carbonate of ammonia on the hairs of Drosera rotundifolia are detailed in Insectivorous plants, pp. 141–8. In Insectivorous plants, pp. 110–12, CD described experiments on the digestive powers of Drosera, in which he had used ‘pure gelatine in thin sheets’ given him by Hofmann.
3
The International Exhibition ran from 1 May to 1 November 1862 at South Kensington, London. Of the foreign nations represented, France had the largest number of exhibitors, several of whom were awarded medals for their exhibits of glues and gelatines (Reports by the juries, class 4, section B, p. 4).

Please cite as “DCP-LETT-3623,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-3623