A field method for the rapid determination of hydrogen cyanide in air

Abstract

A field test for determining small amounts of hydrogen cyanide in industrial atmospheres is based on formation of a Prussian blue colour on test paper impregnated with ferrous sulphate and sodium hydroxide. The test is specific for hydrogen cyanide. The behaviour of a number of possibly interfering gases has been investigated. The test is sensitive to slightly less than 1 p.p.m. of hydrogen cyanide in air and has an error of f 10 to 20 per cent.Test papers properly prepared and stored retain their activity for a t least 10 months.The blue stains obtained are permanent.TWO field tests for the detection and approximate estimation of hydrogen cyanide in air are described in "Methods for the detection of toxic gases in industry-Leaflet No. 2" (Department of Scientific and Industrial Research).l One of these, the benzidinecopper acetate test, has been widely used, but it has certain drawbacks, e g . , difficulty in controlling the critical moisture content of the test paper, instability of the reagents, of the prepared test paper and of the stains on the test paper after treatment with hydrogen cyanide, and lack of specificity. The alternative Congo red-silver nitrate test shares some of these drawbacks.Tests based on formation of a Prussian blue colour from hydrogen cyanide, which would have the advantages of specificity and permanence of pigment, have usually been regarded as insufficiently sensitive and unsuitable for use as field tests.2 Gettler and Gold-baum3 determined the amount of hydrogen cyanide in solutions by aerating at 90" C and passing the gas through test paper previously impregnated with ferrous sulphate and sodium hydroxide to form blue stains of various intensities. These authors claimed that the test papers would retain their usefulness for several weeks if stored in a cool dark place. Our tests showed, however, that test papers prepared as described were sometimes unsatisfactory, and that anyway the papers could not be relied upon to retain their full activity after a few hours. We finally succeeded in establishing the conditions necessary for a test based on formation of a Prussian blue colour, which was free from the various drawbacks already mentioned. EXPERIMENTAL TEST PAPERS-The success of the method depends largely on the correct preparation and storage of the test papers. These are prepared by immersing filter-paper in ferrous sulphate solution, drying, immersing in sodium hydroxide solution and again drying.Reactions within the test fi@ev-The two reagents that are incorporated in the test paper can react with each other and with atmospheric carbon dioxide or oxygen. Ferrous hydroxide, which is initially formed by the action of sodium hydroxide on the ferrous sulphate, can be preserved for long periods in spite of a reputation for instability. Shipko and Douglas4 have shown that ferrous hydroxide in contact with saline solution containing either excess of hydroxide or of ferrous ions is stable for periods up to 6 months if oxygen is rigorously excluded. When the dried paper already impregna...

Spezieller Teil

“…Die durch BRUNSWIK (1921) beschriebene Methode für den mikrochemischen HCN-Nachweis ist zweifellos für biologische Zwecke ebenfalls sehr geeignet; sie beruht auf der Bildung von Silbercyanidkristallen im hängenden Tropfen (1 % AgN03) über der Reaktionskammer (Objektträger + Glasring); sie erlaubt den Nachweis von ~ 0,06}lg HCN, was Prüfung kleiner Pflanzenfragmente auf Cyanogenese ermöglicht. Auch die für Blausäure absolut beweisende Bildung von Berlinerblau, Fe4(Fe[CN]6)3, kann auf Filtrierpapier ausgeführt werden (SEIFERT 1955;DIXON 1958) und die weniger untrügliche, aber sehr empfindliche Phenolphthalinprobe (Abb. 163) wurde durch THrERY (1907) an Ausführung auf Filtrierpapierstreifen angepaßt.…”