Letter, from Antoni van Leeuwenhoek to the Royal Society, dated at Delft Signed autograph Observations of silver deposits on Leeuwenhoek's hands after he had experimented with mixtum (mixture of gold and silver) and aqua regia (mixture of nitric acid and hydrochloric acid); treating a horny induration on Leeuwenhoek's third finger with vitriol, and then with aqua fortis (nitric acid and sulphuric acid) Read to the Royal Society on 21 March 1705 Original figures no longer exist English translation is EL/L3/75 Transcribed and translated in 'Alle de brieven van Antoni van Leeuwenhoek', edited, illustrated and annotated by Committee of Dutch Scientists, vol 15, p 113 English translation printed in 'Philosophical Transactions', vol 24, no 295, p 1794 3 March 1705