...; transferred from the Ministerie van Marine (Department of the Navy), The Hague, to the museum, 1883

Object number: NG-MC-868

Float of a hydrometer to determine the specific gravity of fluids.

The float is stored in a round leather case, filled with flax and sawdust (damaged). It has a glass bulb, weighted with a ball of mercury, which has been sealed off with sealing wax. The narrow upper end or stem, now missing, has a rolled paper scale inside, from 5 to 20 with a ‘W’ at the top, which has survived.

The original numbering of the hydrometers (NG-MC-868, NG-MC-869 and NG-MC-870) is probably incorrect: according to Obreen,¹¹J.M. Obreen, Catalogus der verzameling modellen van het Departement van Marine, The Hague 1858, no. 868. numbers 869 and 870 ought to be Burnett’s hydrometers, but number 870 has a different scale, which makes it more likely to be the one by Kyan.

The specific gravity of a fluid is obtained by immersing the hydrometer, also called ‘the float’, in the fluid: it will float vertically because of the weight of the mercury and the scale can be read at the surface. Hydrometers of this kind are also called ‘densimeters’ or ‘aerometers’. Different designs use different scales.

Pike’s Illustrated Catalogue of Scientific and Medical Instruments, New York 1856, pp. 224-27; J.M. Obreen, Catalogus der verzameling modellen van het Departement van Marine, The Hague 1858, no. 868; P.H. van Cittert, ‘Over vochtwegers’, De Natuur (1928), p. 265 and De Natuur (1929), pl. 1; Sesam Technische Encyclopedie, Wiesbaden, 3 vols., Baarn 1982, pp. 127-28; G.l’E. Turner, Nineteenth-Century Scientific Instruments, London/Berkeley 1983, pp. 89-94

J. van der Vliet, 2016, 'possibly Burnett, Hydrometer Float in a Case, United Kingdom, c. 1800 - c. 1858', in J. van der Vliet and A. Lemmers (eds.), Navy Models in the Rijksmuseum, online coll. cat. Amsterdam: https://data.rijksmuseum.nl/20054010