Hofmann voltameter - wikipedia Hofmann voltameter This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( October 2008 ) Hofmann voltameter A Hofmann voltameter is an apparatus for electrolyzing water, invented by August Wilhelm von Hofmann ( 1818 -- 1892 ) in 1866. It consists of three joined upright cylinders, usually glass. The inner cylinder is open at the top to allow addition of water and an ionic compound to improve conductivity, such as a small amount of sulphuric acid. A platinum electrode is placed inside the bottom of each of the two side cylinders, connected to the positive and negative terminals of a source of electricity. When current is run through Hofmann 's voltameter, gaseous oxygen forms at the anode and gaseous hydrogen at the cathode. Each gas displaces water and collects at the top of the two outer tubes. Contents 1 Name 2 Uses 3 See also 4 References Name The name ' voltameter ' was coined by Daniell, who shortened Faraday 's original name of `` volta - electrometer ''. Hofmann voltameters are no longer used as electrical measuring devices. However, before the invention of the ammeter, voltameters were often used to measure direct current, since current through a voltameter with iron or copper electrodes electroplates the cathode with an amount of metal from the anode directly proportional to the total coulombs of charge transferred ( Faraday 's law of electrolysis ). The modern name is `` electrochemical coulometer ''. Although the correct spelling of Hofmann contains only one ' f ', it is often incorrectly depicted as Hoffmann. Uses The amount of electricity that has passed through the system can then be determined by weighing the cathode. Thomas Edison used voltameters as electricity meters. ( A Hofmann voltameter can not be used to weigh electric current in this fashion, as the platinum electrodes are too inert for plating. ) A Hofmann voltameter is often used as a demonstration of stoichiometric principles, as the two - to - one ratio of the volumes of hydrogen and oxygen gas produced by the apparatus illustrates the chemical formula of water, H O. However, this is only true if oxygen and hydrogen gases are assumed to be diatomic. If hydrogen gas were monatomic and oxygen diatomic, the gas volume ratio would be 4 : 1. The volumetric composition of water is the ratio by volume of hydrogen to oxygen present. This value is 2 : 1 experimentally ; this value is determined using Hofmann 's water voltameter. See also Timeline of hydrogen technologies References Jump up ^ von Hofmann, A.W. Introduction to Modern Chemistry : Experimental and Theoretic ; Embodying Twelve Lectures Delivered in the Royal College of Chemistry, London. Walton and Maberly, London, 1866. ( 1 ) Jump up ^ Frank A.J.L. James, ( 1991 ), The correspondence of Michael Faraday, IET, ISBN 0 - 86341 - 249 - 1, letter 872, 9 / 1 / 1836 Articles related to electrolysis / Standard electrode potential Electrolytic processes Betts electrolytic process Castner process Castner -- Kellner process Chloralkali process Downs cell Electrolysis of water Electrowinning Hall -- Héroult process Hofmann voltameter Kolbe electrolysis Materials produced by electrolysis Aluminium ( extraction ) Calcium metal Chlorine Copper Electrolysed water Fluorine Hydrogen Lithium metal Magnesium metal Potassium metal Sodium metal Sodium hydroxide Zinc See also Electrochemistry Gas cracker Standard electrode potential ( data page ) Electrology Retrieved from `` https://en.wikipedia.org/w/index.php?title=Hofmann_voltameter&oldid=785667542 '' Categories : Electrolytic cells Hydrogen technologies Hydrogen production Hidden categories : Articles needing additional references from October 2008 All articles needing additional references Talk Contents About Wikipedia Deutsch Español فارسی Français Italiano Nederlands 日本 語 Polski Português Română Русский Српски / srpski 中文 Edit links This page was last edited on 14 June 2017, at 19 : 28. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: apparatus used to determine the volumetric composition of water
Answer: Hofmann voltameter