Sprengel, Hermann Johann (DNB12)

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SPRENGEL, HERMANN JOHANN PHILIPP (1834–1906), chemist, born at Schillerslage, near Hanover, on 29 Aug. 1834, was the second son of Greorg Sprengel, a landed proprietor, of Schillerslage.

After early education at home and at a school in Hanover, he attended the universities of Göttingen and of Heidelberg, where he graduated Ph.D. in 1858. Next year he came to England and acted as an assistant in the chemical laboratory of Oxford University. Three years later he removed to London to engage in research at the Royal College of Chemistry and at Guy's and St. Bartholomew's hospitals. From 1865 to 1870 Sprengel held a post at the chemical works of Messrs. Thomas Farmer, Kennington, becoming a naturalised Englishman.

Sprengel was the first who described and patented in England a number of substances called safety explosives. They were of two kinds, liquid and solid. The liquid ones were, in general, solutions of nitrated hydrocarbons—chiefly nitrobenzene or picric acid in nitric acid, mixtures that could be exploded with considerable effect by a detonator. Sprengel allowed his patents to lapse, deriving no pecuniary benefit. Patents subsequently taken out by Hellhoff for the explosive ’Hellhoffite' and by Turpin for 'Panclastite' were essentially the mixtures suggested by Sprengel (O. Guttmann). In a paper read before the Chemical Society, 'On a New Class of Explosives which are Non-explosive during their Manufacture, Storage, and Transport' (Journal Chem. Soc. 1873), Sprengel described these substances and gave a list of combustible agents. The mixtures were to be exploded by fulminate detonators wrapped in dry guncotton, a method called by Sprengel 'cumulative detonation' (see Presidential Address, Sir F. Abel, Soc. Chem. Industry, 1883).

Sprengel's most notable achievement was his invention of a mercurial air-pump for the production of vacua of high tenuity by the fall of water or mercury in narrow tubes. This he described in his paper on 'Researches on the Vacuum' before the Chemical Society in 1865. The invention proved of immense service. In the hands of Bunsen, Graham, and Crookes the apparatus opened up departments of physical research of supreme interest; in those of Swan and Edison an era in regard to the incandescent electric light. 'It would be difficult indeed to enumerate the investigations which have owed their success to the invention of the Sprengel mercury pump' (Lord Rayleigh, Presidential Address, Royal Society, 1906); for details of its practical applications, see Chemical News, 1870; The Times, 29 Dec. 1879 and 2 Jan. 1880; and S. P. Thompson's The Development of the Mercurial Air-Pump, 1888).

Sprengel described to the Chemical Society other researches of practical bearing in 'On the Detection of Nitric Acid' (Journal, 1863); 'A Method of Determining the Specific Gravity of Liquids with Ease and Great Exactness' (1873); 'An Air-bath of Constant Temperature between 100° and 200° C (1873). To the 'Chemical News' he contributed the papers on ’Use of the Atomiser or Spray-producer in the Manufacture of Sulphuric Acid' (1875); 'Use of Exhaust Steam in the Production of Sulphuric Acid' (1887); and 'An Improvement in the Production of Sulphuric Acid' (1887).

Sprengel was elected a fellow of the Chemical Society in 1864, and served on the council (1871-5). He became F.R.S. on 6 June 1878. In 1893 the German emperor conferred on Sprengel the honorary title of royal Prussian professor.

At the latter part of his life Sprengel alleged that his rights of priority with regard to certain inventions and discoveries had been infringed, and his caustic letters to the publlc press detailing his grievances were reprinted in book form, with notes, as: 'The Hell-Gate Explosion in New York and so-called "Rackarock," with a few words on so-called Panclastite' (1886); 'Origin of Melinite and Lyddite' (1890); and 'The Discovery of Picric Acid (Melinite, Lyddite) as a Powerful Explosive, and of Cumulative Detonation, with its Bearing on Wet Guncotton' (1902; 2nd edit. 1903).

Sprengel died unmarried at 54 Denbigh Street, London, S.W., on 14 Jan. 1906, and was buried in Brompton cemetery.

[Chem. Soc. Trans., vol. xci.; Journal Soc. Chem. Industry, vol. xxv.; Engineering, vol. lxxxi.; VIIth International Congress of Applied Chemistry (explosives section: Rise and Progress of the British Explosives Industry—portrait); O. Guttmann's Manufacture of Explosives, 1895; Roy. Soc. Catal. Sci. Papers; Poggendorff's Handworterbuch, Bd. III, 1898; Ency. Brit. vol. xxii. (11th edit.); Nature, 25 Jan. 1906; The Times, 17 Jan. 1906; Men of the Time, 1899.]

T. E. J.