ANALYTICAL E D I T I O N
138
Vol. 6, No.2
TABLE111. COMPARISON OF ANALYSISOF SILICON AND FERROI n all the fusions which have been considered in this article, SILICON FUSED WITH SODIUM AMIDE AND WITH SODIUM it is probable that mixed aquo-ammono silicates, aluminates, CARBONATE etc., are primary products of the reactions, but whether these SODIUM CARBONATEare further converted to sodium ammono silicates, alumiFUSION SODIUM AMIDEFUSION FUSION nates, etc., is a matter of conjecture. TIMEAT WBIQHTOF Weight of Per cent Per cent
B U B S T A N C E ~ 330° C. Hours Ferrosilicon 9
SAMPLE
of Si
of Si
0.8027 0.7996
76.4 76.6
75.6
(1) Bergstrom and Fernelius, Chem. Rev., 12, 75-6, 90, 92, 106, (2) Bergstrom and Fernelius, Ibid., 12, 75,83. 84 (1933).
8102
Gram
Grams
0.4980 0.4944
151-2 (1933).
Ferrosilicon
4
0.6033 0.4998
0.7709 0.7667
71.9 71.7
76.6
Ferrosilicon
6
0.2001
0.3083
72.0
75.6
Silicon
9b
0.4887 0.4968
1.0353 1.0268
96.9 96.73
96.7
Silicon
4
0.4871 0.4980
0.9258 0.9252
87.06 86.8
96.8
0
b
LITERATURE CITED
200 mesh. 20 grams of NaNHz used per analysis. 6 per cent NaNs added.
(3) Dennis and Browne, J . Am. Chem. Soc., 26,587-600 (1904). (4) Fernelius, Dissertation, Stanford University, 1928. (5) Franklin, J . Am. Chem. SOC.,27, 820-51 (1905); Franklin and Kraus, Am. Chem. J.,21,8-14 (1899); Franklin, Ibid., 47,285 (1912); Proc. Eighth Intern. Congress Applied Chem., 6, 119 (1912); J . Am. Chem. Soc., 46, 2134-51 (1924). (6) Hillebrand, U.8. Geol. Survey, Bull. 700 (1919). RECEIVED August 26, 1933. From the master’s and doctoral theaes of P. Victor Peterson, Stanford University, 1923 and 1930. The maater’n thesis was prepared under the direction of E. C. Franklin.
Inclusion of Rarer Metals in Elementary Qualitative Analysis I. Inclusion of Tungsten and Molybdenum in Groups I and I1 LYMANE. PORTER, University of Arkansas, Fayetteville, Ark.
D
URING more than a hundred years (3) the list of
metals found in the general scheme of elementary qualitative analysis has remained practically unchanged. In the light of the growing commercial importance of some metals not found in the original list, it has seemed advisable to introduce a few of the more important rarer metals by modifying and simplifying certain procedures from schemes for the analysis of the rare elements (1, 2, 4) and incorporating them into the scheme for the commoner ones. The detection of tungsten in group I and of molybdenum in group I1 is described in this paper, and detection of titanium and vanadium in group I11 will be described later. Stock solutions of the common ions are made up in the customary manner. For tungsten and molybdenum, the alkali salts of the tungstate and molybdate are dissolved in water and diluted to the proper concentration.
DETECTION OF TUNQSTEN IN GROUP I The sample, which may include a BUS ended precipitate, is treated with dilute h drochloric acid untifprecipitation appears complete, and 5 cc. o?the acid are added in excess. This mixture is warmed just below the boiling point for 2 or 3 minutes, and cooled, in order t o make the recipitate of tungstic acid or tungstic oxide more complete. :1 the material is boiled, some or all of the mercurous ions will be oxidized, provided nitrates are also present. The cooled mixture is filtered two or three times through the same pa er if necessary to obtain a clear filtrate which is reserved for rater groups. Certain acid ions-namely, arsenate, arsenite, phosphate, borate, oxalate, tartrate, vanadate, and to a less extent acetate-interfere with the completeness of the tungsten recipitation, so that combinations of these with tun sten shourd be avoided. The separation of the lead chloride by f o t water and the identification of mercurous mercury by the use of ammonium hydroxide are accomplished in the customary manner. The ammoniacal filtrate from the mercury will contain the silver and the tungsten, This solution is then made nearly neutral with dilute hydrochloric acid, and enough ammonium hydroxide is added just t o redissolve any precipitate that may have appeared, The silver may now be identified and separated by the addition of a soluble iodide followed by filtration. In the presence of a large excess of ammonia, the precipitated silver
iodide i s colloidal, and it is difficult to remove it by filtration. This test for silver has been shown to be fully as sensitive as the usual one using nitric acid t o precipitate the silver chloride. After filtration, the solution is evaporated to a small volume, acidified with dilute hydrochloric acid, and treated with 3 cc. of stannous chloride. After the mixture has been heated to boiling, 3 cc. of concentrated hydrochloric acid are added, and the mixture is again boiled. The formation of tungsten blue proves the presence of tungsten. Test solutions were run by this method using widely varying concentrations of the constituent ions. Tungsten was found correctly in all cases where there was as much as 10 mg. of this metal in the solution, in the presence of even as much as 400 mg. of other metals of group I. I n the hands of a class, satisfactory results were obtained with samples in which the concentration of each constituent present was approximately tenth normal,
DETECTION OF MOLYBDENUM IN GROUPI1 Molybdenum belongs in the arsenic division of the hydrogen sulfide group. I n order to effect a satisfactory separation of the molybdenum sulfide, however, the procedure for the precipitation of the group should be modified. The filtrate from grou I is neutralized with ammonium hydroxide and is made sightly acid with dilute hydrochloric acid. To this are added 2.5 cc. of concentrated hydrochloric acid, 1 gram of ammonium iodide, and enough water t o make a total volume of 100 cc. This mixture is then saturated with precipitation flask hydrogen sulfide in the cold in a and the flask, loosely sto pered, is p aced in a beaker of boiling water. When the water [as again reached boiling temperature, boiling is continued for 4 or 5 minutes, after which the mixture is cooled, resaturated with hydrogen sulfide, and filtered.
fressure
This procedure has been shown to precipitate satisfactorily all the members of this group. Of the commonly mentioned ions that interfere with the precipitation of molybdenum sulfide, the presence of phosphate must be avoided, because of the formation of a complex compound that prevents
March 15, 1934
INDUSTRIAL AND ENGINEERING CHEMISTRY
precipitation of the sulfide. I n the presence of arsenic in the trivalent or the pentavalent state, interference is experienced only when there is a small amount of molybdenum with a relatively large amount of arsenic. The precipitation is satisfactory if there is not much more than two or three times as much arsenic as molybdenum. Reducing ions, such as stannous tin, should be avoided on account of their action upon the molybdate, which reduces the sensitivity of the sulfide test. Tests were run which showed that the addition of the iodide is necessary for the precipitation of arsenic, and that it does not interfere with precipitation of molybdenum. In the usual treatment of the residual sulfides of group I1 with ammonium polysulfide, molybdenum dissolves as (“4)~MoS4, and from this the sulfide may be re recipitated by the use of dilute hydrochloric acid, along with t i e other sulfides of this division. When the antimony and stannic sulfides have been dissolved out in warm concentrated hydrochloric acid, the remaining sulfides of arsenic and of molybdenum are dissolved in warm dilute nitric acid. This solution is then made ammoniacal and the arsenic is precipitated by the addition of magnesia mixture. The solution must be stirred vigorously to be sure that the arsenic does not remain in a supersaturated solution. After the removal of the arsenic by filtration, the molybdenum will be present in the solution as ammonium molybdate. If this is now acidified with dilute hydrochloric acid and treated with ammonium or potassium thiocyanate in the cold, followed by a few drops of stannous chloride, a deep red solution of MoO(CNS)a is formed, proving the presence of molybdenum. Any
139
iron that may be present as an impurity will be reduced by the stannous chloride and will not interfere with the test. Test solutions with varying quantities of other constituents were analyzed successfully for molybdenum. A positive test for molybdenum was obtained from a solution of 20 mg. of molybdenum (as metal) in the presence of a total of 600 mg. of other metals such as antimony, mercury, copper, and cadmium. A weaker test was obtained in the analysis of a similar solution including also 100 mg. of arsenic in the form of sodium arsenate. For student use, however, the proportion of molybdenum to other constituents should be more comparable. (Under these latter conditions satisfactory results have been obtained with a class of second-year chemistry students.) LITERATURB CITED (1) Browning, P. E., “Introduction to the Rarer Elements,” 4th ed., Wiley, 1917. (2) Noyes, A. A., and Bray, W. C., “A System of Qualitative Analysis for the Rarer Elements,” Macmillan, 1927. (3) Rose, Heinrich, “Manual of Analytical Chemistry,” Tr. by Griffin, Thomas Tegg, London, 1831. (4) Schoeller, W. R., and Powell, A. R , “Analysis of NIinerals and Ores of the Rarer Elements,” Lippincott, 1919.
RECEIVED July 25, 1933 of Arkansas.
Researoh Paper 334, Journal Series, Univernity
New Absorption Tube G. E. LEWORTHY Fuel Research Laboratories, Ottawa, Ontario, Canada
A
NEW type of absorption tube, which has been designed packed with glass wool, to act as an additional trap to any for the determination of hydrogen in ultimate analysis by sulfuric acid which might be carried over during the operacombustion, consists of three glass tubes, joined together to tion. When ready for use the apparatus weighs approximately form B single unit, and so arranged as to facilitate the clean100 grams and can be used on any chemical balance. The ing and m n g of the apparatus. I n preparing the apparatus for use, the ground-glass stop apparatus is weighed and the inlet tube F is joined flush with pers E are removed and the tubes filled to the leveling mark the outlet tube of the furnace by means of rubber tubing. D with concentrated sulfuric acid by means of a finely drawn At the end of the operation the caps are replaced and the out Dbet or buret. care being taken to remove any sulfuric apparatus is again weighed, the increase in weight by the following equation giving the acidkiich may adhere to thepercentage of hydrogen in the ground surface before lubrisample : cating. It has been found advisable to use a stiff lubri11.19 X increase in weight cant for the stoppers, as a weight of sample sudden evolution of gas may raise the stoppers when a Ten samples of coal were lighter lubricant such as vasedetermined in duplicate, in line is used. Sulfuric acid is e a c h case checking within used because of its great 0.0015 gram, without changaffinityforwater, andinorder ing the absorbent. The adthat the rate of the flow of gas vantage of this tube over a may be observed. t r a i n of calcium chloride The smaller tube is filled tubes as commonly used is a t w i t h c o t t o n wool, coarsely once apparent. It is strong powdered anhydrous copper and rugged, although lightly sulfate, and granular magm a d e ; it is self-contained; nesium perchlorate trihyand a single weighing takes drate. The anhydrous copper t h e place of a number of sulfate’acts not only as an weighings, which results not absorbent but as an indicator only in greater accuracy but to warn of the exhaustion of in a considerable saving of the reagents by turning a blue time. color. The inlet tube is loosely FIGURE1. DIAGRAM OF APPARATUB RECSIV~D October 23, 1933.
