Rapid Method for Determination of Sulfur in Brass and Bronze J. 0. COONEY,The Chesapeake and Ohio Railway Co., Huntington, W. Va.
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HE following method of analysis is one developed by the necessity of rapidly determining the sulfur content of phosphor bronze-bearing metals, the usual method of removing the metals by solution in nitric acid and electrolysis being too time-consuming for use in this case. The method depends on the solution of the sample in cupric ammonium chloride and the consequent precipitation of the sulfur as metallic sulfide, which is filtered off, oxidized, and the sulfur precipitated in the usual manner with barium chloride. The method has the advantage, other than saving time, of being indifferent to the amount of sulfur contained in the sample, whereas, in the regular method referred to above, it has been noted that in cases of unusually high sulfur content, some of the sulfur escapes oxidation and floats on the surface in elemental form and will be lost if extraordinary precaution is not taken. The method may be adapted to materials other than brass or bronze, the only limiting factor being the possibility of dissolving the metal in the reagent used. Metals below copper in the electrochemical series will, of course, not dissolve and will be precipitated with the sulfur and, if present in any considerable amount, will cause trouble in the subsequent operations. Antimony up to as high as 5 per cent does not interfere seriously, and amounts larger than this are rarely met with in brass or bronze. The solution used can be regenerated with chlorine gas in the same manner as that used for carbon determinations in steel. It is not necessary to run a blank on the solution if it is filtered before use, although blanks should be run on the other reagents used. SOLUTIONREQUIRED.Cupric ammonium chloride (CuC12.2NH4C1 2H20). One part of the salt to 3 parts of water and 5 per cent of hydrochloric acid added. Use in the proportion of 12 grams of salt to 1 gram of metal. METHOD.Dissolve 5 grams of the brass or bronze, as finely divided as possible, in the required amount of solution, using gentle heat and stirring the solution occasionally. When everything is in solution except the gray to black sulfide residue and any traces of carbon, antimony, bismuth, etc., that may be present, remove from the heat and let stand for a few minutes. Do not allow to cool before filtering, for lead chloride may precipitate. Filter on a sulfur-free asbestos mat, using suction, and remove the main portion of the filtrate before washing so as not t o dilute the cupric solution unnecessarily before regeneration. Wash the mat and residue with 5 per cent hydrochloric acid and then with water, and remove the mat to a 400-cc. Pyrex beaker, using as little water as possible to wash out the last traces of precipitate. Add concentrated nitric acid equal to the amount of water in the beaker, then 10 cc. of saturated bromine water, and boil until the bromine is expelled. The nitric acid will dissolve any metallic residues in the precipitate and set free any sulfur that may be occluded by them. After the bromine is expelled, dilute with an equal volume of water and filter rapidly from the asbestos fiber, a piece of absorbent cotton being convenient for this filtration. Add about 0.5 gram of sodium bicarbonate to the filtrate, heat to dryness, bake to remove the nitric acid, and dehydrate any silica that may have dissolved from the asbestos. Dissolve in 5 cc. of hydrochloric acid and 25 cc. of water, bring
to a boil, and filter from siliceous matter, washing the filter paper with hot 5 per cent hydrochloric acid. The sulfur is precipitated as barium sulfate in the filtrate, with a 10 per cent solution of barium chloride. If the brass is heavily leaded or contains more than traces of antimony, it is best to add sufficient c. P. granulated zinc to the solution before filtering from the siliceous matter. This will precipitate all the heavy metals and they will be filtered off with the siliceous matter. Samples of Bureau of Standards phosphor bronze No. 63, recommended sulfur value 0.06, gave the following results by the above method: 0.063, 0.063, 0.066, 0.062, and 0.067. The same standard with 0.2 gram of antimony metal added to each determination gave the following: 0.060, 0.065, 0.065, 0.061, and 0.059. Samples of 50-50 lead-copper piston-packing metal analyzing 0.40 per cent sulfur by carefully controlled electrolytic methods gave by this method 0.426, 0.434, 0.436, 0.430, and 0.427. The method has been in continual use in this laboratory for about six months and has been entirely satisfactory. The time required from the weighing of the sample to the precipitation of the sulfate is less than one hour and is so arranged that the barium sulfate is allowed to settle overnight. The important feature in this case is that the electrolytic apparatus is free for use in the remainder of the analysis, and one man can carry along all determinations simultaneously. RECEIVED May 29,1931.
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Corrosion Test on Casinghead Gasolines A. W. TRUSTY, Louisiana Oil Refining Corp., Shreveport, La.
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HE A. S. T. M. requirement for corrosion test is that a copper strip shall be immersed in the gasoline in a test tube and maintained a t 122' F. (50" C.) for 3 hours. The following short method has been used in this laboratory: To 10 cc. of gasoline in a test tube add two drops of mercury and shake. If no black precipitate of mercury sulfide is formed, and if the surface of the mercury remains bright, the corrosion test will be negative. If a black precipitate is formed, the regular A. 5. T. M. test should be made. Most casinghead gasolines and some straight-run gasolines contain practically no sulfur, and the above test verifies negative corrosiveness for routine samples. This test, of course, does not apply to cracked gasolines, refinery absorption gasoline, or other comparatively highsulfur gasolines. R E C ~ I VSeptember ED 9, 1931
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