FEBRUARY 15,1939
ANALYTICAL EDITION
after air-drying. On the other hand, when 5 grams of urea are taken for 200 ml. of solution containing 5 ml. of concentrated hydrochloric acid and the hydrolysis is allowed to proceed overnight at 80" to 90" C. the error is reduced to +0.2 per cent or less for amounts of calcium equivalent to 0.25 to 0.5 gram of calcium carbonate. For smaller amounts of calcium (0.05 to 0.1 gram of calcium carbonate) under these conditions there is a distinct tendency for the positive error to increase, which is attributable mainly to coprecipitation of oxalic acid; in one case (No. 8) the error amounted to +0.6 per cent. The oxalate content of precipitates 10, 11, and 12 as determined by permanganate titration indicates that there is appreciable coprecipitation of ammonium oxalate, acid calcium oxalate, or oxalic acid with the smaller amounts of calcium oxalate, under the conditions of precipitation used. The larger amounts of precipitate (Nos. 1 and 5) show a normal oxalate content. If the precipitate is dried a t 105" C. the results are closer to the theoretical than when the precipitate is air-dried, but this method is not recommended because of the possibility of loss of hydrate water (see No. 3, Table 11, in which some decomposition took place after long heating at 105" C.). The coprecipitation of sodium is marked (Table 11, No. 15) and only small amounts (No. 16) may be present unless a reprecipitation is made. Magnesium is not appreciably coprecipitated when present in small amounts, as shown by determinations 17 and 18 of Table 11; these results indicate that even if a precipitate of calcium oxalate is badly contaminated by magnesium it can be freed from the latter element if the reprecipitation is made by the urea-hydrolysis method.
Recommended Procedure Prepare a solution of calcium salt containing the equivalent of 0.2 t o 0.5 gram of calcium carbonate in 175 to 200 ml. of solution, add 5 ml. of concentrated hydrochloric acid, and heat nearly t o the boiling point. Add 1.0 gram of ammonium oxalate monohydrate dissolved in approximately 20 ml. of hot water (no precipitate should form) and then 5.0 grams of reagent quality urea dissolved in a similar volume of cold water. After mixing, heat at 80" to 90" C. until the solution is distinctly basic to methyl orange (overnight). Cool the solution and collect the precipitate in a orous porcelain, sintered-glass, or Gooch crucible which has Been weighed after standing 10 t o 15 minutes in the air. Wash the precipitate with small portions of cold water and then with three or four 2-ml. portions of reagent quality acetone. Draw air through the crucible for 5 to 10 minutes and weigh. It is well t o let the crucible stand on the balance pan for 10 to 15 minutes after the first weighing, and then t o reweigh to be certain that the weight is constant. In the presence of appreciable amounts of sodium or magnesium the first precipitation of calcium oxalate may be made by the ordinary method, and after washing with dilute ammonium oxalate solution the precipitate may be dissolved in hydrochloric acid and reprecipitated as described in the previous paragraph; in this case the amount of ammonium oxalate added in the final precipitation need not be more than 0.2 to 0.3 gram.
Summary Calcium oxalate monohydrate precipitated from neutral or ammoniacal solutions, or by neutralizing a hydrochloric acid solution with ammonia, retains foreign water after washing with acetone or alcohol and ether, and air-drying. Drying the precipitate a t 105" C. and above yields results closer to the theoretical than does air-drying a t room temperature, but this method of drying cannot be recommended without reservation because considerable amounts of water may still be retained, constant weight is not always easily attained, and the precipitate may lose monohydrate water in a dry atmosphere. If calcium oxalate is precipitated slowly from an acid solution by gradual neutralization of the acid by the hydrolysis
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of urea, it may be weighed as the monohydrate after washing with acetone. The solution, containing 5 ml, of concentrated hydrochloric acid per 200 ml., is treated with 5 grams of urea and digested a t 80" to 90" C. until the acid has been neutralized. I n this manner results accurate to approximately 0.2 per cent can be obtained with 0.2 to 0.5 gram of calcium carbonate; with amounts of calcium corresponding to 0.05 to 0.1 gram of calcium carbonate results tend to be high.
Literature Cited (1) Dick, J., 2. anal. Chem., 77,358 (1929); 83, 105 (1930). (2) Fowler, R. M., and Bright, H. A., J. Research Natl. Bur. Standards, 15,493 (1935). (3) Goy, S., Chem.-Ztg., 37, 1337 (1913). (4) Haslam, J., Analyst, 60, 668 (1935). (5) Moser, L.,and Zombory, L. von, 2.anal. Chem., 81,95 (1930). (6) Sandell, E. B., and Kolthoff, I. M., J. Phys. Chem., 37, 153 (1933). (7) Wassiljew, A. A., and Sinkowskaja, A. K., 2. anal. Chem., 89, 262 (1932). (8) Willard, H. H., and Boldyreff, A. W., J. Am. Chem. SOC.,52,1888 (1930). (9) Willard, H. H., and Chan, F. L., Willard and Furman's "Elementary Quantitative Analysis," 2d ed., p. 319, New York, Van Nostrand Co., 1936. RECEIVED July 29, 1938.
Glass Liner for High-pressure Hydrogenation Bomb EMANUEL B. HERSHBERG AND NATHAN WEINER Harvard University, Cambridge, Mass.
T
HE glass container shown in the accompanying figure has proved satisfactory as a liner for high-pressure hydrogenation bombs. It has been constructed in net capacities of 10 and 30 cc., and the design is feasible for larger volumes. The body of the liner should fit the bomb snugly and, as shown, the joint should be rimless. A steel compression spring maintains closure and prevents rotation of the liner. Correct alignment of the gas inlet tube is assured by a mark on the rim of the male member of the joint which corresponds with the upper end of the constricted tube. A circular mark around the body of the tube about 5 mm. below the gas inlet serves as a reference point for calibration. The authors have not succeeded in repairing broken liners which had been used a t high temperatures and high pressures of hydrogen, owing to apparent absorption and retention of gas, which is liberated a t glass-working temperatures causing the glass to froth.
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RECEIVED November 19, 1938.
