INDUSTRIAL AND ENGINEERING CHEMISTRY
518
With the simplification of procedure, impetus should be given to the teaching of micro- and semimicrodeterminations. All the troublesome and involved techniques are a distinct deterrent when time is a factor.
number of samples may a t first appear large, but as tubes are conditioned by means of a tube conditioner while the second combustion is run, the absorption tubes can be weighed and a new sample made ready for combustion during the sweeping out.
TABLE I. REPRESENTATIVE RESVLTS (An analytical balance of sensitivity 40 was used, and approximations of the fourth figure were made in the usual manner) H20 COz H C H C Substanoe Sample Found Found Found Found Calcd. Calcd.
MQ.
MQ.
MQ.
%
%
p-Nitrochlorobenzene 2 0 . 7 0 4 . 7 7 3 4 . 7 0 2 . 5 6 4 5 . 7 1 34.80 8 . 1 0 58.28 2.58 45.66 Thiourea 20.30 9 . 6 1 11.80 5 . 2 6 15.85 Benzoic acid 15.84 7 . 0 4 40.04 4 . 9 4 68.94 20.70 9 . 2 2 52.36 4.95 68.98 34.62 1 5 . 4 0 8 7 . 4 0 4 . 9 4 6 8 . 8 6 Arsanilic aoid 22.60 7 . 5 8 27.54 3.73 33.23 3 3 . 8 5 11.20 4 0 . 8 0 3 . 6 8 3 3 . 2 0 2,4-Dinitrophenol 13.40 2 . 6 0 19.18 2.16 39.04 15.26 2 . 9 6 2 1 . 8 2 2 . 1 6 3 9 . 0 0 2,4-Dichloroaniline 20.40 5 . 7 1 33.26 3 . 1 1 44.46 22.80 6 . 4 0 37.20 3 . 1 2 4 4 . 4 9 35.64 9.90 58.10 3.09 44.46 p-Dichlorobenzene 23.42 5 , 8 0 42.00 2.76 48,91 34.00 8 . 5 0 61.05 2 . 7 8 48.97 1 8 . 9 2 5 . 5 2 31.42 3 . 2 4 4 5 . 2 9 Bromobenzene p-Aminobenzoic acid 2 5 . 4 3 11.70 5 7 . 0 0 5 . 1 0 6 1 . 1 3
%
%
2 . 5 4 45.71 5.30 15.78 4.92 68.82 3.71 33.18 2 . 1 9 39.12
Summary A method for filling absorption tubes is discussed whereby combustion time can be materially lessened for semimicrosamples and for microsamples. The substitution of silver supported on asbestos for silver wool increases the efficiency of the combustion tube in the removal of halogen. Combustions under increased pressure ensure completeness of oxidation and removal of halogen, sulfur, nitrogen, etc. Absorptions under pressure ensure complete removal of water and carbon dioxide.
3.11 44.45 2.74 48.93 3 . 2 1 45.23 5.11 61.28
With two platinum boats and four absorption tubes, the in running as many as sixteen author has had no samples in 8 hours (the first sixteen results in Table I). The
VOL. 11, NO. 9
Acknowledgment The author is indebted to Mr. Weiskopf of the Technicon Co., New York, N. Y., for his cooperation in the development of this apparatus, and for furnishing combustion tubes of various sizes.
Literature Cited (1) Natelson, Brodie. and 10, 609 (1938).
Conner, IND.ENC.CHEM.,Anal. Ed.,
A Generator for the Production of Pure Carbon Dioxide EDGAR J. POTH, Stanford University School of Medicine, San Francisco, Calif.
T
HE author (2, 3) has described generators which con-
sistently produce carbon dioxide of the high purity required in Pregl’s microcombustion method of estimating nitrogen. Modifications of this equipment ( I , 4 ) have corrected some of the imperfections of the original apparatus but, unfortunately, introduced complications and other defects. A simplified form of the apparatus is represented in the figure. Chambers A and B are conveniently made from 2- and 1-liter Pyrex flasks. The construction of the acid delivery tube, F, ensures a smooth feeding of small drops of solution and eliminates after-drops. The t i p should be drawn down to a dia m e t e r of a p p r o x i mately 1 mm. Beginning with the g e n e r a t o r completely empty it is charged as follows: With the generator lying on its side, 170 CO. of concentrated sulfuric acid diluted with 150 cc. of water are introduced into B through E and C, and the acid remaining in C is displaced w i t h a i r a n d washed into B with 25 cc. of water. With the generator in the up-
right position, a solution of 500 grams of potassium acid carbonate dissolved in 1100 cc. of water is run into A through D, followed by 100 cc. of water t o rinse out the stopcock and bubble trap. The system is evacuated with a vacuum pump through D and E simultaneously for about 15 minutes. Mercury is introduced into the manometer and trap, C, and the generator is set in operation as outlined in a previous publication (5)2 Trap C is constructed with the volume of the inner and outer chambers about equal. Should the pressure in the system, for any reason, fall so low as to break the mercury seal, mercury will be forced into B, and its presence will show that the system has been contaminated with air. In this event the apparatus must be completely emptied and rechar ed. Any drops of mercury which cannot be removed from Eulb B by ordinary means should be dissolved with nitric acid, and the apparatus thoroughly washed to remove nitrates, C is placed in a diagonal position in such a manner that when it is forced the bubbles of gas will travel u one wall. Thus the entire column of mercury cannot be foreelinto the upper bulb, to prevent action of the trap. Since the solid potassium sulfate formed in the generator is water-soluble, the generator can be cleaned by running water in a t D and out a t E . After emptying the generator of water, it is ready for recharging. This generator will deliver pure carbon dioxide with small fluctuations of pressure, is compact and sturdy, and can be used for the generation of gases other than carbon dioxide. This piece of apparatus is available from E. H. Sargent and Company, Chicago, Ill.
Literature Cited (1) Lowe,
E.W.,and Guthmann, W. S., IND.ENQ.CHEM.,Anal.
(3) Ibid., 3,202 (1931). (4) Shelberg, E.F., Zbid., 10,704 (1938).
