# Dictionary of National Biography, 1885-1900/Porrett, Robert

​PORRETT, ROBERT (1783–1868), chemist, son of Robert Porrett, was born in London on 22 Sept. 1783. When he was eleven years of age he ‘amused himself by drawing up and writing out official papers for his father,’ who was ordnance storekeeper at the Tower of London. These productions led the war office officials to offer to keep him in the department as an assistant. He was appointed in 1795, promoted later to be chief of his department, and retired on a pension in 1850, when his services received official acknowledgment. He died on 25 Nov. 1868, unmarried. Robert Porrett Collier, lord Monkswell [q. v.], was his nephew.
Porrett was elected fellow of the Society of Antiquaries on 9 Jan. 1840 and of the Royal Society in 1848. He was an original fellow of the Chemical Society, and also a fellow of the Astronomical Society. His position and residence in the Tower led him to take an interest in antiquities. He was a recognised authority on armour, on which he contributed several papers to ‘Archæologia’ and the ‘Proceedings’ of the Society of Antiquaries.
Although he was not a professional chemist, Porrett did valuable work in experimental science. Towards the end of 1808 he found that by treating prussic acid with sulphuretted hydrogen a new acid was formed, which he termed prussous acid. For this investigation he was awarded a medal by the Society of Arts. In 1814 he discovered the qualitative composition of the acid, and showed that it was formed by the union of prussic acid and sulphur, and termed it sulphuretted chyazic acid. Its present name of sulpho-cyanic acid was given by Thomas Thomson (1773–1852) [q. v.] (Thomson's Annals of Philosophy, xii. 216), and its quantitative composition was determined in 1820 by Berzelius. In 1814 Porrett also made the important discovery of ferrocyanic acid, which he termed ferruretted chyazic acid. He showed by the electrolysis of the salts, then known as triple prussiates, and by the isolation of the acid itself, that the iron contained in the salts must be regarded as forming part of the acid, thus confirming a suggestion previously put forward by Berthollet (Kopp, Geschichte der Chemie, iv. 377). He examined the properties of the acid carefully, and showed that it can easily be oxidised by the air, Prussian blue being formed at the same time; this observation has been utilised in dyeing (Porrett in Philosophical Transactions, 1814, p. 530, and Watts, Dict. of Chemistry, ii. 227). Porrett attempted to determine the quantitative composition of prussic acid, and showed that when it is oxidised the volume of carbonic acid formed is exactly twice that of the nitrogen. But his other data are erroneous, and the problem was completely solved by Gay-Lussac shortly after. Porrett in 1813 made some interesting experiments in conjunction with Rupert Kirk and William Wilson on the extremely dangerous substance, chloride of nitrogen.
His ‘Observations on the Flame of a Candle,’ a paper written in 1816, contain important and hitherto neglected confirmation of Davy's then just published view of ​the structure of luminous flame, recently defended by Smithells (Chem. Soc. Trans. 1892, p. 217). According to Porrett, the light is mainly due to free carbon formed in the flame owing to the decomposition by heat of gaseous hydrocarbons. His ingenious experiments deserve repetition, and the observation that the luminous portion of the flame is surrounded completely by an almost invisible mantle, and that a spirit-lamp flame, though more transparent than glass, casts a shadow when placed in front of a candle flame, are of much importance. His chemical investigations on gun-cotton, published in 1846, are not of great value.
Porrett's sole contribution to physics was the discovery of electric endosmosis in 1816 (Thomson, Annals of Philosophy, viii. 74). The phenomenon had, according to Wiedemann (Galvanismus und Elektricität, 1st ed. i. 376), been observed previously by Reuss, but Porrett's discovery was independent, and the phenomenon for long went in Germany by his name.
Porrett's style is clear and unpretentious, his exposition methodical and workmanlike. Probably owing to lack of time, he did not attain the technical skill necessary to complete the investigations he began so brilliantly. It is unfortunate for science that a man of such marked capacity should have given to it only his leisure. The following is a list of his scientific papers: 1. In the ‘Transactions’ of the Society of Arts: ‘A Memoir on the Prussic Acid’ (1809, xxvii. 89–103). In Nicholson's ‘Journal:’ 2. ‘On the Prussic and Prussous Acids’ (1810, xxv. 344). 3. ‘On the Combination of Chlorine with Oil of Turpentine’ (1812, xxxiii. 194). 4. ‘On the Explosive Compound of Chlorine and Azote’ (in conjunction with R. Kirk and W. Wilson) (1813, xxxiv. 276). In the ‘Philosophical Transactions:’ 5. ‘On the Nature of the Salts termed Triple Prussiates, and on Acids formed by the Union of certain Bodies with the Elements of Prussic Acid’ (6 June 1814, p. 527). 6. ‘Further Analytical Data on the Constitution of Ferruretted Chyazic and Sulphuretted Chyazic Acids,’ &c. (22 Feb. 1815). In Thomson's ‘Annals of Philosophy:’ 7. ‘Curious Galvanic Experiments’ (1816, viii. 74). 8. ‘Observations on the Flame of a Candle’ (viii. 337). 9. ‘On the Triple Prussiate of Potash’ (1818, xii. 214). 10. ‘On the Anthrazothion of Von Grotthuss, and on Sulphuretted Chyazic Acid’ (1819, xiii. 356). 11. ‘On Ferrochyazate of Potash and the Atomic Weight of Iron’ (1819, xiv. 295). In the Chemical Society's ‘Memoirs:’ 12. ‘On the Chemical Composition of Gun-Cotton’ (in conjunction with E. Teschemacher) (1846, iii. 258). 13. ‘On the Existence of a new Alkali in Gun-Cotton’ (iii. 287).
P. J. H.