Detection of War Gases Hydrocyanic Acid and Chlorpicrin PAUL F. FENTON University of Vermont, Burlington, Vermont
HE WORK to be reported here is an extension of a recent publication1 on the use of silica gel tubes in T the detection of war gases. Since i t has been suggested that hydrocyanic acid might be used in gas warfare, it was thought advisable to develop a method of detecting this chemical agent. A special detector tube was made up containing silica gel mixed with a small amount of solid ferrous sulfate. Air contaminated with HCN was aspirated through the detector tube. The silica gel was then wetted with strong alkali (20 per cent KOH) and the tube heated over a burning match. Following this a few drops of ferric chloride in hydrochloric acid (equal parts of 5 per cent ferric chloride and concentrated hydrochloric acid) were added to the tube. A deep blue color developed, indicating the presence of HCN. This test was based in principle on the prussian blue reaction described in Treadwell-Hall.= Even in the absence of HCN a greenish color developed in the detector tube following the addition of the alkali. This was due to the formation of ferrous bydroxide. The color disappeared when the ferric chloride-hydrochloric acid solution was added. Care must be taken not to confuse this reaction with a positive test for HCN. The color of ferrous hydroxide does not disappear rapidly when the acid ferric chloride reagent is added, and it is advis1 FBNTON, ''Vapor detector tubes and detector kit for some chemical agents used in gas warfare," J. CHEM.Eouc., 20,
-
664-5, 1943.
TREADWELL-HAL.L, '*Analytical Chemistry," John Wiley and Sons,Inc., New York, 1937, volume I, pp. 327-8.
able to make the reagent pass over the silica gel several times by alternate suction and pressure. If one has determined by means of the available test papers that the war gas present is not a vesicant, several tests may be carried out successively in the same detector tube. For example, using the silica gel-ferrous sulfate tube it is possible, after aspiration of the contaminated air, to test fist for chlorpicrin using dimethylaniline.' If no reaction is obtained, test for phosgene (diphenylamine and dimethylaminobenzaldebydel). If this reaction too is negative, carry out the above test for HCN. If such an analytical sequence is used, care must be taken to use minimal amounts of each reagent. A special detector tube may be prepared for chlorpicrin. Silica gel was impregnated with dimethylaniline and tubes, filled with this gel, used directly to test for chlorpicrin. A bright yellow-orange color develops. The advantage of this test is that i t does not require a special reagent for use in the field. Reagents in the tube, however, decompose after a time. The impregnated silica gel turns green, thus obscuring the actual color reaction with chlorpicrin. Tubes have been prepared in this laboratory which still gave satisfactory tests after one month of storage. It has been found advisable to discard the rubber pressure bulb for the aspiration of contaminated air through the detector tubes. A glass syringe (10 or 20 ml., preferably ungaduated) is much more efficient and less bulky.
