March 15. 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
tiously using a bath of lukewarm water. Allow at least 45 minutes for the evaporation of 100-cc. samples, and a t least 1.5 hours for 500-cc. samples, when using the Swartz U-tubes. The Fleming jar requires 45 minutes for 100-cc. samples and a t least 4 hours for 500-cc. samples. The rate of evaporation is limited by the back pressure of the absorption train and the danger of blowing out stoppers. At the close of the evaporation, shut off the stopcocks in the same manner as a t the end of the preliminary run and weigh the tubes, using the tare tube as counterpoise. 100 M 1.48 X cc. sample = % moisture
Where 1.46 is the specific gravity of sulfur dioxide at its boiling point a t atmospheric pressure, M is the gain in weight of the first phosphorus pentoxide tube less the increase or plus the decrease in the second or compensating phosphorus pentoxide tube.
RESIDUE TEST The residue left b y the evaporation of refrigeration-grade sulfur dioxide is too small for a quantitative determination to be practicable. Hence, i t is determined microscopically and compared with a standard. PROCEDURE. Use a 200-cc. cylindrical sample container having a 1-cc. tip which at its lowest portion is graduated to 0.01 cc. Clean this container with cleaning solution, rinse with distilled water, and dry at 120' C. The glass surface should be bright and free of all film. Wipe the cylinder valve and flush. Draw a 100cc. sample without using any sample connection. Stopper the container either with rubber stopper and Bunsen valve or with a plug of cotton wool. Evaporate to dryness and compare with standard. SULFURICACID After evaporation of the sulfur dioxide and careful removal of all sulfur dioxide vapor, as shown by iodine test, the sulfuric acid is titrated with 0.01 N caustic. Use a 125-cc. Erlenmeyer flask, with a calibraPROCEDURE. tion mark at the 100-cc. point. Clean with chromic acid cleaning solution, wash out thoroughly, and dry at 120' C. Evaporate a 100-cc. sample, using a plug of cotton wool to stopper the flask. After the evaporation, remove sulfur dioxide vapor by connecting a Gooch crucible adapter to suction and applying the rubber end to the flask, then breaking the connection. Repeat fifteen times until no odor of sulfur dioxide remains and a drop of 0.01 N iodine added to the flask is not decolorized. Prepare water for the titration by adding 2 drops of methyl red and adjusting by means of either 0.01 N sodium hydroxide or 0.01 N hydrochloric acid to the exact neutral point. Add 25 cc. of this water to the flask and titrate with 0.01 N sodium hydroxide. cc. X N X 0.04904 X 100 = cc. of SO, X 1.46
%
79
NONCONDENSABLE GASES The 100-cc. sample of sulfur dioxide gas is collected in a 100-cc. gas buret and potassium hydroxide added. The residual gas is read as noncondensable gases. The results for small amounts of noncondensable gases are read directly to 0.02 per cent and may be estimated t o 0.005 per cent. REAQEST. 30 er cent potassium hydroxide solution. APPARATUS.T i e buret is similar to Eimer and Amend, No. 28940, except that it is of 100 cc. capacity and the upper tip is graduated in 0.02 cc. down to the 0.2-cc. mark. PROCEDURE. With pinchcock H closed, open the cock between A and C, and raise the mercury leveling bottle until the mercury just comes into the cup C. Close the stopcock B, leaving a small globule of mercury in the cup. Place the cylinder containing the liquid sulfur dioxide on its side so that the ramshorn of the lower valve is in the liquid phase. Connect the apparatus as shown in the diagram. With the spring pinchcock G open, the cylinder valve is cautious1 opened until liquid sulfur dioxide runs out at the tube and I . &ome analysts find it more convenient to substitute the use of one foot for pinchcock G . ) The pinchcock H is now o ened, the buret stopcock turned into the position shown in the iagram, and the pinchcock G and the cylinder valve closed. When the liquid sulfur dioxide has vaporized as indicated by the globule of mercury, the cylinder valve is opened to allow liquid sulfur dioxide to escape into the tubing only as fast as it will vaporize. Allow the gas to sweep out the air in the a aratus, which should be accomplished in 2 or 3 minutes. wft! pinchcock G closed, quickly turn stopcock B so that it is open between the cylinder and the buret A , lower the leveling bulb and fXl the buret with sulfur dioxide as. Close pinchcock H and open pinchcock G. Turn stopcoca B so that it is open between A and C and run this buret full of gas to waste through cup C, as it is used only to treat with any small amount of potassium hydroxide left from a previous determination. Refill the buret in the same manner as before with exactly 100 cc. of sulfur dioxide under atmospheric pressure. Close pinchcock H and turn stopcock into the position shown in the diagram. Add through cup C about 15 to 20 cc. of the potassium hydroxide solution, being careful to exclude all air. After the contraction has ceased, bring the level of the mercury in the bulb to that in the buret and read the volume of residual gas. eo. of residual gas =
% noncondenaable gases in liquid phase
LITERATURE CITED (1) Flenner, A. L., and Caverly, W. R., Refrigerating Eng.,21, No. 5, 344 (1931). (2) Scribner, A. K., IND. ENQ.CHEM.,Anal. Ed.. 3, 255 (1931). RECEIVED November 3, 1932.
Note on Washing the Potassium Cobaltinitrite Precipitate W. E. THRUN,Valparaiso University, Valparaiso, Ind.
T
HE precipitate of potassium cobaltinitrite obtained in
of sulfuric acid and the oxidizing agent, the precipitate
micromethods (1-4) for determining potassium becomes increasingly flocculent upon washing with water. It is therefore usually washed in centrifuge tubes by siphoning. It was found that when the precipitate is washed with a dilute solution of aluminum sulfate (1 per cent) it will be much less flocculent, so that it can be washed b y the usual method of drainage after inversion. Three washings with 3 cc. of solution are usually sufficient. If the supernatant liquid from the second washing is not nearly colorless, a fourth washing should be performed. It was also found t h a t more consistent results can be obtained when the precipitate is to be titrated indirectly with solutions of permanganate or ceric sulfate if, upon addition
is thoroughly stirred for a while when the tube containing the reacting substances is placed in boiling water. Because of the instability of nitrous acid ( I ) , ceric sulfate should be a better oxidizing agent for this purpose than permanganate, as it furnishes a positive ion to oxidize a negative ion.
LITERATURE CITED (1) (2) (3) (4)
Jacobs and Hoffman, J. Biol. Chem., 93, 685 (1931). Kramer and Tisdall, I b i d . , 46, 339 (1921). Leulier, Velluz, and Griffon, Bul. SOC. chim. biol., 10, 1238 (1928). Tisoher, Biochern. Z., 238, 148 (1931).
RECEIVED Auaust
11, 1932.
