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
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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.
