1032
ANALYTICAL CHEMISTRY
bath the rate of hydrolysis reaches an optimum for analytical conditions. The time required for complete precipitation of barium sulfate was determined by adding a tenfold excess of solid sulfamic acid to a solution containing approximately 150 mg. of barium in 100 ml. of water and recording the time from the appearance of the initial turbidity until a portion of the supernatant liquid no longer gave a precipitate upon the addition of sulfuric acid. The time varied from 8 to 12 minutes for complete precipitation. Samples containing 1 to 100 mg. of barium were analyzed by the following procedure: The barium sample was diluted t o approximately 100 ml., 1 gram of solid sulfamic acid was added, and the solution was placed on the steam bath. The solution was heated for about 30 minutes after the first turbidity appeared to allow for complete precipitation and a short digestion period. The solution n-as filtered through a weighed Selas porcelain filtering crucible (No. 3001), and the precipitate was washed with hot distilled water and ignited to constant weight in a muffle furnace at a minimum temperature of 900' C. Temperatures loxver than 900' C. gave high results. Results of the determination of barium in a pure standard solution by the sulfamic acid procedure and by the standard sulfuric.
acid procedure are shown in Table I. To study the effect of foreign ions on the determination of barium, precipitations in the presence of known amounts of the ions were made using the same procedure as given above. The results are shown in Table 11. CONCLUSION
The determination of barium through the homogeneous precipitation of barium sulfate by the slow hydrolysis of sulfamic acid gives excellent results. This method yields coarse crystals which are more easily filtered and washed free of adsorbed ions than Jhose obtained by the standard sulfuric acid procedure. Several foreign ions, particularly calcium and iron, cause little interference. Strontium in all but trace amounts interferes. LITERATURE CITED
Butler, hf. J., Smith, G. F.,a n d h d r i e t h , L. F., IXD. ENG.CHEM., ASAL.ED.,10,690 (1938). (2) Elving, P. J., and Van Atta, R. E., -IKAL. CHEM.,22, 1375 (1950). (3) Oberhauser, B. F., and Urbina, C. H. E., Anales facultad filosof. 2/ educatidn, Unia. Chile, Seccidn qu.lm., 3, 109 (1946). (4) Killard, H. H., ASAL. CHEM.,22, 1372 (1950).
(1)
K E C E I F ~for D reriew April 13, 1 9 5 1 .
Iccebted December 26, 1951.
Microturbidimetry for the Detection of Hydrogen Cyanide FRED BROWN'
AND
JAMES GR.4HAM
University College of North IVules, Bangor, .Vorth W'ules
MJRIBER of sensitive tests foi cyanide have been described 'I The method due to Fox (2) was found to be the simplest in practice and gave very satisfactory results. The (2-8).
method consists of passing a stream of air through the solution under test and thus carrying the cyanide into a suspension made from potassium hydroxide, potassium iodide, and a very small quantity of silver nitrate. The silver iodide is dissolved by the cyanide and the turbidity of the detecting solution disappears. Katurally, the cyanide in the test solution must be in volatile form and to this end the solution should be acidified (or otherwise treated) so that the cyanide will volatilize as hydrogen cyanide Biological material is usually digested with hot dilute sulfuric acid. I n using this method the authors have devised an improvement in technique which renders the method more cei-tain and enables it to be extended to detect smaller quantities of cyanide. PROCEDURE
Tests were carried out on a solution of 25 nil. of concentrated sulfuric acid in 250 ml. of water containing the requisite quantity of cyanide added as potassium cyanide solution. These conditions were chosen to simulate those that might be found in biological applications of the method, and have no special virtue in so far as the detection of cyanide is concerned. I n thic method the acidified cyanide solution is boiled, the water condensed by a reflux condenser, and the hydrogen cyanide carried on by a stream of air. The detecting solution is similar to that used by Fox ( 2 ) and consists of 5% potassium hydroxide (1 ml.), 5% potassium iodide (1 drop), and 0 001 M silver nitrate (1 drop). For additional sensitivity the 0.001 Jf silver nitrate was replaced by 0.00025 llf silver nitrate (1 drop). This solution is contained in a simple glass huhbler oi small dimensions, such that the 1 ml. of detecting solution fill. the bubbler to a depth of about 2 em. This detecting solution ir illuminated by means of a narrow beam of light, prrhaps 2 mni. in diameter, and is viewed against a dark background in a darkened room. The turhidity of the solution shons clearly as a brilliant Tyndall cone and the clearing of the solution by the cyanide is very easily 1 Present address, Atomic Energy Commission. Chalk Riser, Ontario, Can ad a.
seen. As the turbidity is SO much more easily viewed, it is possible to mork with extreniely dilute suspensions without any uncertainty. The air stream was such as to give a reasonably fast rate of bubbling and nas turned off temporarily while observing the Tyndall effect. AgNOa in Detecting Solution 0 001 JI, 1 drop
Cyanide Used (as H C X ) , M g . 0.1
0 00025 -11, 1 drop
0.01 0.01
Result of Test Positive Doubtful Positive
Control tests carried out in the abbence of cyanide always showed negative results, provided the laboratory contained no opened bottles of cyanides or cyanide solutions. The original method used 0.001 -11silver nitrate under normal circumstunces, but by using 0.00025 X silver nitrate the limit of detection was 1 part in 2 X lo6. This corresponds roughly to 0.1 nig. of hydrogen cyanide in the present experiments. R i t h 0.00025 Jf silver nitrate and normal lighting there was considerable doubt as to whether or not the turbidity of the detecting solution had cleared. R i t h the dark ground illumination, however, the 0.00025 J!f silver nitrate presented no difficulty and 0.01 nig. of hydrogen cyanide could easily be detected in 250 nil. of water. The concentration corresponds to 1 part in 2.5 x 107. The amount of cyanide required to dissolve the silver iodide from 1 drop of 0.00025 M silver nitrate is on the order of 0.001 mg., so that it is unlikely that this method can be extended to very much loLyer limits than those obtained. LITERATURE CITED
(1) Aldridge, W. N., Analyst, 69, 262 (1944). (2) Fox, D. L., Science, 79,37 (1934). (3) Kolthoff, I. M., 2.Anal. Chem., 57, 11 (1918). (4) Martini, Mikrochemie, 26, 241 (1939). ( 5 ) Nicholson, R. I., Analyst, 6 6 , 189 (1941). (6) Schales. O., Ber., 71,447 (1938). (7) Viehoever, A., and Johns, C. O., J . Am. Chem. SOC.,37, 601 (1915). ( 8 ) Waller, 4. D., Ibid., 35, 406 (1910). RECEITEDfor review September 8, 1951. Accepted January 21, 1962.
