AUGUST 15, 1938
AKALYTICAL EDITION
precipitates which have entered the buret tip can easily be washed out. The type of calomel electrode used is shown in Figure 4. The goose-neck type of liquid junction, described by Clark ( I ) , has proved to be the most suitable for an apparatus of this kind. The liquid junction is made by applying gentle suction at G with stopcock H slightly open and L dipping into the solution to be examined. The solution flows into the small bulb, K , and a sharp junction with the heavy potassium chloride solution can be formed in the middle of bulb K . This procedure is facilitated by a calibration on tube G . The capillary, L, has a length of about 8 mm. and an internal diameter of 1 mm. There is no detectable diffusion of potassium chloride into the solution in the vessel during the time required for an experiment, when using this form of liquid junction. Agar-agar bridges, on the other hand, allow fairly large amounts of salt to diffuse into the solution to be titrated. An aluminum vessel serves as an oil thermostat. The oil used is a mixture of equal parts of transformer oil (Shell K 2) and white spirit. This mixture does not smell or evaporate and has about the optimal viscosity. All metal parts are earthed. S o further
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screening is necessary, and glass electrodes give perfectly steady potentials even when stirring. The freedom from rubber connect,ions makes the apparatus very suitable for titrations in organic solvents. Furthermore, the absence of any external stirrer simplifies titrations which have to be carried out in an inert gas atmosphere. The photograph in Figure 1 shows the apparatus ready to be lowered into the oil bath for a n experiment. All glass parts are made from Pyrex or Jena glass. A microapparatus has been constructed on the same line., taking from 2 to 10 cc. of solution to be examined.
Literature Cited (1) Clark, W. hf., “Determination of Hydrogen Ions,” 3rd e d . , p. 301, Baltimore, Williams &- Wilkins Co., 1928. RECEIVED April 26, 1938.
Determination of Sulfur in Some of the More Common Alloys LOUIS SILVERMAN 2129 Wightman St., Pittsburgh, Pa.
T
HE copper chloride-perchloric acid method ( 2 ) for sulfur is applicable to certain ferroalloys as well as to many
types of monels; and to nickels, cobalts, and nickel-cobalt alloys. These latter dissolve rather slowly.
nonferrous alloys.
Brass Bureau of Standards Sample No. 63 may be considered representative. I t s percentage composition is: S 0.06, Cu 78.05, P b 9.74, Sn 9.91, Sb 0.55, As 0.19, Zn 0.48, F e 0.27, and P 0.62. The Bureau of Standards method is based on the preliminary separation of tin oxide, the removal of copper and lead by electrodeposition, and the removal of nitric acid by hydrochloric acid and heat. The proposed method is more rapid, requires much less manipulation, and is less difficult. The results indicate the same order of precision, but are 0.01 Fer cent higher in value. Transfer 5 grams of brass to a 600-cc. beaker PROCEDURE. and cover with 500 cc. of potassium-copper chloride solution. Maintain the solution at about 90” C. as on a steam bath. Mechanical stirring is preferred. Keep the solution covered as much as possible. When all copper has dissolved, filter the warm solution through a fast filter paper, and wash n-ith hot water. Remove the paper from the funnel, place it in the beaker, cover with strong bromine water, and agitate n-ith a glass rod. Add 10 cc. of zinc oxidenitric acid soluticn and 8 cc. of perchloric acid. Heat the beaker to destroy the paper and to drive out the nitric acid and the excess perchloric acid. When perchloric acid begins t o condense at the top of the beaker, remove the beaker from the hot plate and allow to cool. Dissolve the residue, usually solid, in n-ater, dilute to about 100 cc., and boil to remove chlorine. Filter off any insoluble matter on paper, and wash n-ith hot water. Dilute the filtrate to 200 cc. and precipitate sulfates with barium chloride. The weight, of barium sulfate divided by 5 and multiplied by 0.1373 gives the weight of sulfur found per gram. REAGEKTS:500 grams of (KC1)2CuC12.2Hy0,100 cc. of hydrochloric acid, and 2000 cc. of water. Sift 200 grams of zinc oxide into 1 liter of concentrated nitric acid. RESULTS:0.072, 0.071, and 0.070.
Nonferrous Alloys The same procedure has been applied to pure copper and to its alloys of tin, lead, zinc, iron, and aluminum; to various
Ferromanganese Using Bureau of Standards S o . 68 (S, 0.014 per cent) as a test sample, i t was found that the copper chloride solution must be added cold, after which the procedure is as usual for ordinary steels. Results: 0.014. 0.013 per cent. hlanganese metals seemed to contain not more thrin 0.003 per cent of sulfur.
Ferromolybdenum Lundell (1) used a hot tube method, or a n aqua regia solution method. Apparatus for the first is not usually available, and for the second method the advantages of the copper chloride method apply ( 2 ) . The only modifications to be applied to the above procedure are:
A smaller sample is used: 3 grams. Agitation of the alloy in copper chloride solution must be continued until nearly all the iron and molybdenum are dissolved. I n the third paragraph of the procedure, the insoluble matter contains molybdic acid and is washed with hot 0.5 per-cent (by volume) hydrochloric acid instead of distilled water. K i t h these extra precautions not more than 0.0002 gram of molybdenum was found in any barium sulfate precipitates of ferromolybdenum. Converting this value to barium molybdate and calculating to sulfur, no error was found in reporting the result as pure sulfur (to two significant figures). Results: KO.30747: 0.11, 0.11, 0.11, 0.12. S o . 4626: 0 2 5 ( I ) , 0.22, 0.23. The results obtained with brass and ferromolybdenum were checked b y O m n Gates, U. S. S a v y Laboratory, Munhall, Pa.
Literature Cited (1) Lundell, Hoffman, and Bright, “Chemical Analysis of Steel,” p. 454, Kew York, John Xiley &. Sons, 1931.
(2) Silverman, Louis, IKD. EXG.CHEY.,Anal. E d , 7, 205 (1935). RECEIVED April 21, 1938.
