Determination of Cadmium Oxide Suspended in Air H. A. BEWICK', A. J. CRUIKSHANKz, AND F. E. BEAMISH, Department of Chemistry, University of Toronto, Toronto, Ontario, Canada A modification of the 8-naphthoquinoline method for the determination of semimicroquantities of cadmium obtained on filtration of air in a test chamber contaminated with cadmium oxide dust is described. The paper filters and organic dust were destroyed by a wet method, the copper and other interfering metals were removed, and the cadmium was precipitated by &naphthoquinoline in the presence of potassium iodide. The amount of cadmium present was determined from the Lang cyanide titration of the iodide resulting from the decomposition of the cadmium-iodine-8-naphthoquinoline complex.
D
solution 0.5 ml. of chloroform was added and the liauid was shaken. Sulfurous acid: sulfur dioxide gas bubbled into distilled water t o give a nearly saturated solution.
URING the study of the toxicity to animals of a gaseous
mixture of air and cadmium oxide in a 550-liter test chamber, a rapid method was required for determining the proportion of cadmium oxide. The air was filtered through dried weighed Whatman No. 50 filter papers (5.5-cm.), supported on a coarse wire screen in a &ita filter holder. The efficiency of filter papers for the collection of suspended cadmium oxide has been studied by Silverman and Valeneuela (a). The filters were destroyed with sulfuric and nitric acids and the interfering elements in the dust.were removed by means of iron wire in acid solution. The cadmium was determined by a modification of Pass and Ward's d-naphthoquinoline method (1) for cadmium. This complex was filtered and decomposed with potassium hydroxide, and the liberated iodine was titrated in hydrochloric acid-potassium cyanide aolution with standard potassium iodate solution.
PROCEDURE
The paper with the cadmium oxide deposit was transferred to a dry, wide-mouthed 100-ml. Pyrex conical flask with a lip, fitted with a small funnel. Three milliliters of concentrated sulfuric acid were added t o the flask on the hot plat'e. The paper was allowed to char for 1.5 minutes and then 1 ml. of red fuming nitric acid was added slowly from a buret. Second and third additions of 0.5 ml. were made a t 1-minute intervals. If the plate was hot enough this procedure resulted in a light yellow solution. Each flask was .then held by tongs over a Meker burner until the nitrogen dioxide was displaced by the white fumes of sulfur trioxide. A darkening of the solution a t this point indicated that organic matter was still present. The flasks were cooled and 30 ml. of hydrazine hydrate solution were added. The hydrazine facilitated the removal of the oxides of nitrogen. About 90 cm. (3 feet) of coiled iron wire were added to each and the mixture was heated to just below boiling for 15 minutes. Reduction for 15 minutes v-as sufficient to remove at, least 24 mg. of copper from solution. The solutions were filtered hot through Pyrex fritted crucibles (capacity 15 ml., porosity M). The flask and crucible were washed twice with water. The filtrate and washings were transferred to a 250-ml. beaker, about 0.25 ml. of sulfurous acid and 20 ml. of Rochelle saltpotassium iodide solution mere added, and the solution was stirred well. The volumes of 8-naphthocjuinoline reagent indicated below were then added with stirring: 9 ml. for 25 mg. of cadmium oxide, 12 ml. for 50 mg., and 15 ml. for 75 mg. The precipitate was allon-ed to stand for about 15 minutes and then filtered by suction through a Coors porcelain Gooch crucible, No. 3, cont,aining a mat of asbestos. The asbestos (J. T. Baker, Powminco) was well ground witb a little water in a mortar before being used, to hasten the dissolving of t,he precipihte. Most of the precipitate was t'ransferred to the Gooch. The beaker was washed txvice with 15 ml. of wash liquid, and 5 ml. more of wash liquid were used to wash the precipitate in the Gooch. The beaker was completely drained and the Gooch sucked dry. The dry asbestos mat and precipitate were removed with a stirring rod to the original beaker. A little dry asbestos was added to the Gooch, moistened slightly with water, rubbed around the crucible with a stirring rod to loosen any particles, then washed into t'he beaker with distilled water. The volume of water was kept lox in this transference. The solid was broken up with the flattened end of a stirring rod and then stirred vigorously for about half a minute to disintegrate the precipitate further. Five milliliters of the concentrated potassium hydroxide solution were added and the beaker held in a pair of tongs was heated with swirling over a low hleker flame. This mixture bumped easily. The mixture was then stirred vigorously for 2 minutes. Any particles .of precipitate were ground with the Bnd of a st,irring rod, then 16 ml, of concentrated hydrochloric acid were added gradually down the side of the beaker, so that any adhering particles were washed into the solution. This warm mixture was stirred vigorously for 0.25 minute. The beaker was set in a shallow dish of cold running water; a large number of beakers may be cooled a t the same time. T o the cooled mixture (below 30" C.) 5 ml. of 10% potassium cyanide solution were added and then the standard pot'assium iodate was added slowly with continued stirring.
REAGENTS
Standard cadmium solution was prepared by dissolving about Fifteen milliliters of concent,rated sulfuric acid were added, and the mixture was fumed, then diluted with 0.5 ml. of water, and fumed again. The solution, finally made up to 2.000 liters, contained a total of about 120 ml. of concentrated sulfuric acid. Nitric acid, red fuming (J. T. Baker). Sulfuric acid, concentrat'ed C.P. Hydrazine hydrate solution: 10 ml. of hydrazine hydrate (B.D.H., ,Cert. Chem., 50% w/w, NH1.TU"2.H20) diluted to 500 ml. wit'h distilled water. Iron wire, KO. 36 (J. T. Baker). Rochelle salt-potassium iodide solut'ion: 25 grams of potas3ium iodide (Llerck, reagent, granular) and 125 grams of potassium sodium tartrate tetrahydrate (Merck, reagent, small crystals) dissolved in 425 ml. of water. 8-Naphthoquinoline solution: 12.5 grams of P-naphthoquinoLine (Eastman Kodak S o . 1444) dissolved in a solut,ion of 7 ml. of concentrated sulfuiic acid and 15 ml. of water, diluted to 50 ml., and filtered. This filtrate was diluted to 500 ml. Dilute potassium iodide solution: 16 grams of potassium iodide dissolved in water and diluted to 500 ml. Wash liquid: 40 ml. of dilute potassium iodide solution, 40 ml. of 8-naphthoquinoline solution, 1 ml. of sulfurous acid, and 320 ml. of water. Concentrated potassium hydroxide: 420 grams of potassium hydroxide (Merck, reagent, pellets) dissolved in 340 ml. of water. Potassium cyanide solution, loyo: 50 grams of potassium cyanide (Merck, reagent, 95% granular) dissolved in 450 ml. of water. Potassium Iodate, 0.0156 31. Potassium iodate (Merck, reagent, crystalline powder) was dried a t 120' C. for one hour snd allowed to cool in a desiccator; 3.334 grams of t,he iodate were weighed, dissolved, and diluted to 1.000 liter. 1 ml. of 0.0156 d l otassium iodate = 1 mg. of cadmium oxide. Starch golution. Two grams of soluble starch (Merck, reagent, powder) were mixed with a few milliliters of cold water, and about 175 ml. of boiling water were added. The liquid was boiled for several minutes and diluted to 200 ml. To the cooled 2 grams of pure metal in 10 ml. of concentrated nitric acid.
Present address, The Solvay Process Company, Syracuse, N. Y. Present addreaa, National Research Council, Chalk River, Ontario, Canada.
269
ANALYTICAL CHEMISTRY
210 When the end point was approached as indicated by the change t o a light brown color, 2 ml. of the starch solution were added from a buret, the sides of the beaker were washed down, and the titration was continued t o a colorless solution. This part of the procedure was conducted in a fume cupboard because of the formation of hydrogen cyanide. No colored particles of the cadmium complex should be present in the bottom of the beaker. This procedure \ws used for 1 to 75 mg. of cadmium oxide. 1 to 20 mg. required 0.0078 M potassium iodate 20 t o 40 mg. required 0.0156 M potassium iodate 40 to 75 mg. required 0.0312 -1.I potassium iodate
For amounts of cadmium oxide greater than 75 mg. it is recommended that aliquots of the solution obtained after the wet destruction of the filter be used. I n the development of the method aliquots of the standard cadmium solution and a filter paper were added to the conical flasks and the samples were treated as described above. Table I includes some of the results obtained. When the weight of the fume was required, the following procedure vias carried out: Whatman No. 50 (5.5-cm.) a t e r papers were dried in an oven a t 75' C. for 2.5 hours in preparation for weighing, removed from the oven with forceps, and placed immediately in a weighed, flat, polished, metal ointment tin (about 6 cm. in outside diameter), and the lid was tightly closed. The box and the papers were then weighed. The tin was handled and kept clean with a chamois. After the fume had been collected, the paper and fume were dried in the oven, placed in the box, and weighed as described above. The tins were wiped with a chamois before each weighing. The cadmium method outlined above was used for over 1500 determinations in the study of the toxicity of cadmium and cadmium oxide fumes. About twenty-five determinations could be made by one person in 8 hours.
Table I. Results of Cadmium Determinations Sample NO.
Cd Recovered as Oxide M p.
Remarks
Mo. 1.00 25.05 1.97 1.00 5.00 10.01 10.02 25.02 9.85 9.85 9.85 7.43
1.06 25.13 1.95 1 01 5.12 9.90 9.99 25.03 9.70 9.75 10.10 7.47
10-minute settling 10-minute settling 15-minute settling 20-minute settling 20-minute settling 20-minute settling 20-minute settling 20-minute settling 30-minute settling 30-minute settling Overnight settling Standard procedure, 2.5
13
9,85
9.80
14
9.85
9.75
Standard m g . of Cu procedure, 10 mg. of Cu, 12 mg. of A1 Standard procedure, 10 -mg. of Cu, 12 mg. of Zn Standard procedure, 25 mg. of Cu
1 2 3 4 5 6 7 8 9 10 11 12
15
Cd Added as Oxide
74 3
i3 8
droxide instead of 2 N ammonia. The titration was made in the presence of the asbestos and any undissolved complex waa revealed by its purple color after the solutions had become colorless. Pass and Ward used sulfurous acid before the removal of the interfering metals. The complete removal of sulfur dioxide is time-consuming and, if not completely boiled out, sulfur dioxide is reduced during the generation of hydrogen and cadmium sulfide is formed. This proved to be a frequent source of difficulty in the initial experiments. The authors found that the sulfurous acid was not necessary at this point. Ten to 15 minutes rather than one hour was found to be sufficient time for the quantitative formation of the complex. ACKNOWLEDGMENT
DISCUSSION
To dissolve the p-naphthoquinoline complex Pass and Ward used 2 N ammonia and filtered t o remove the asbestos. The authors found this method unsuitable because of the lengthy treatment required. This difficulty was overcome by grinding the asbestos before use, transferring the mat and the precipitate to the original beaker, and using concentrated potassium hy-
The authors wish to acknowledge the assistance of J. E. Currah, J. R. Mills, and D. S. Russell. LITERATURE CITED
(1) Pass, A., and Ward, A. M., Analyst, 58, 667 (1933). (2) Silverman, L., and Valenzuela, C., J. I n d . Hug. Tozicol., 28, 3, 107 (1946).
No.
Detection and Estimation of Microquantities of Cyanide A. 0. GETTLER AND L. GOLDBAUM New York University, New York, .V. Y . OST of the color-producing tests employed for the detection of cyanide possess sensitivity but lack specificity. Only the Prussian blue test and the thiocyanate test are specific for the detection of cyanide, but as ordinarily performed, they are not sufficiently sensitive for the quantitative microdetermination of cyanide. The sensitivity of the Prussian blue test may be enhanced by conducting the hydrogen cyanide, derived from a nitrogen- or cyanide-containing substance, through a piece of filter paper previously impregnated with ferrous sulfate and sodium hydroxide. The test paper is supported in position in a specially designed glass apparatus by a pair of identical glass flanges having finely ground surfaces. PREPARATION OF TEST PAPER
Five grams of hydrated ferrous sulfate are dissolved in 50 ml. of distilled water and any insoluble residue is removed by filtra-
tion. .?. single sheet of filter paper (Whatman KO.50 smooth glazed, acid- and alkali-treated) is immersed in this solution for 5 minutes, then removed from the ferrous sulfate solution, suspended by means of a clamp, and allon-ed to dry in the air. The dried piece of filter paper is then dipped into a 20% sodium hydroxide solution. When the paper is thoroughly wetted, it is removed and again allowed to dry in the air. Circular pieces of the paper, having exactly the same diameter as the ground-glass flanges, are cut out. These test papers will retain their usefulness for several weeks if stored in a cool dark place. GROUND-GLASS FLAXGE CONNECTIONS
The apparatus consists of a twin pair of plane ground-glass flanges of circular cross section. Each flange i s continuous with a length of glass tubing and is fitted with two glass hooks. The glass tubing guides the aerated gases to the test paper, which is tightly held between the two flanges. The glass hooks on each flange are connected t o corresponding hooks on the other flange by means of a stout rubber band n-hich serves t o keep the flanges in close planar contact.
