SEPTEMBER 15, 1936
AZALYTICAL EDITION (2) (3) (4) (5) (6) (7)
ment. Neither of these appellations is satisfactory; neither is sufficiently descriptive of the purpose and the first is in some ways actually misleading. Since the instrument is expected to minimize the effect of radiant energy absorption and increase the transfer of heat by convection, and since the principle is applicable to a.t least two different types of measuring elements, it is suggested that such a piece of equipment be termed an aradiant convection pyrometer.
(8) (9)
(10) (11) (12)
Literature Cited (1) Forrest, Special Report, Mass. Inst. Tech., Dept. Chem. Eng., 1923.
393
Guillon, Chaleur & Ind., 7, 395, 472 (1920). Haslam and Chappell, Bull. Mass. Inst. Tech., 60, No. 80 (1925) Hildebrand, Arch. Wtirmezuirt., 7, 319 (1926). Kreisinger and Barkley, Bur. Mines Bull. 145 (1918). Laoey and Woods, IND.ENQ.CHIM.,27, 379 (1935). Mattocks, Ind. Gas, 13, No. 2, 15 (1934). Monrad, IND.ENQ.CHEM., 24, 505 (1932). Mulliken, Power, 78, 565 (1934). Nusselt, 2. Ver. deut. Ing., 53, 1750, 1808 (1909). Parkin and Winks, J. SOC.Glass Tech., 26, 315-26T (1932). Robinson, J. IND.ENQ.CHEM.,13, 820 (1921).
RncEIvEn November 21, 1935. Presented before the Midwest Regional Meeting, Louisville, Ky., October 31 to November 2, 1935.
Laboratory Gas-Absorption Vessels WILLIAM MCKINLEY MARTIN,l Montana Agricultural Experiment Station, Bozeman, Mont.
T
HE gas-absorption vessels shown in Figure 1 were developed after considerable experimentation with various types of absorbers. They operate on the same principle as the absorbers designed by Weaver and Edwards (8), Milligan (7), Beaumont, Willaman, and De Long ( I ) , and Harvey and Regeumbal (S),but in certain respects are perhaps better adapted for general laboratory use.
gas wherever needed in the laboratory. It has been found especially useful in preparing large volumes of carbon dioxide-free distilled water by the aspiration method. When used for this purpose, the stream of carbon dioxide-free air supplied from the scrubber is dispersed in the water by means of a sintered-glass distributing disk which may be prepared by the methods described by Kirk, Craig, and Rosenfels ( 5 ) , and Cool and Graham (9). The carboy aspiration assembly is shown in C. The air may be forced through the system by either compression or suction, the latter usually being preferable when the aspiration is allowed to run overnight, or when compressed air is not readily available. The efficiency with which carbon dioxide is removed from water by this method
Gas Scrubber Apparatus -4is a convenient and efficient gas scrubber designed to supply a continuous stream of purified air or other 1 Present address. Research Department, American Can Company, Maywood. Ill.
STANDARD ACID
------a
COMPRESSED AIR,
7
D
c
C02 FREE
1
C . -
_ _
1
I A
B
FIGURE1. A. B.
Laboratory gas scrubber. Quantitative gas-absorption vessel in which absorbing solution is titrated directly; a current of carbon dioxide-free air being used to stir and circulate the solution in the vessel during titration.
D
APP.4RATUS
C.
Removal of carbon dioxide from a carboy of distilled water by aspirating with a current of carbon dioxide-free air.
D. .issernbly for stirring solution with a current of carbon dioxide-free air during titration.
396
INDUSTRIAL AND ENGINEERING CHEMISTRY
is obviously determined by the rate of aspiration, the degree of dispersion of the gas stream, and the length of the path of the gas bubbles through the liquid. Using a small water pump of the usual laboratory type, adjusted to draw a gentle stream of air through the system, a 40-liter carboy of distilled water is rendered carbon dioxide-free overnight, or in from 12 to 16 hours. Following aspiration, the inlet to the distributing tube is closed with a pinchcock and the outlet connected to a soda-lime trap, the carbon dioxide-free water being withdrawn as needed through a siphon tube not shown. The scrubber may also be used to supply a current of carbon dioxide-free air to stir soIutions which are affected during titration by carbon dioxide or other reactive atmospheric gases. The stream of purified air not only stirs the liquid during titration and thus permits the operator to observe more closely the approach of the end point, but it also sweeps the atmosphere above the liquid free from carbon dioxide and other interfering gases, thereby obviating errors which inevitably occur when alkaline solutions are exposed to the atmosphere. Although any form of titration vessel may be used, the stirring action is most effective in a cylindrical vessel similar to that shown in D. The solution to be titrated is put into the vessel in a countercurrent of carbon dioxide-free air for the reasons already mentioned. Many other uses may be found in chemical and physical laboratories for a gas scrubber of the type herein described. For example, it may be used not only for purifying gas streams, but also for drying or controlling their moisture contents at any desired degree of saturation. For the latter purpose, the scrubber may be charged with concentrated sulfuric acid, sulfuric acid solutions, or saturated solutions of certain salts (4). When the saturated salt solutions are used in the presence of an excess of the solid salt, a gas stream may be maintained a t a constant degree of saturation continuously over long periods. The scrubber is easily charged with the excess salt by filling it with a hot saturated solution and then allowing it to cool, the amount of salt crystallizing from the solution being determined by the temperature at which the solution is saturated. To prevent closure of the tubes by the crystallizing salt during cooling, air is drawn into the spiral from the inlet jet, after which the outlet tube is closed with a pinchcock. As cooling proceeds, an occasional bubble of air is drawn into the system through contraction, thus keeping the inlet orifice open. The crystallizing salt settles to the bottom of the apparatus where the solution is continually circulated in contact with it to maintain a state of saturation. Obviously, the volume of gas which may be treated without recharging the apparatus will depend on its moisture content and on the quantity of undissolved salt, the latter going into solution when the partial pressure of the water vapor of the gas stream is greater than that of the saturated solution, and crystallizing out when it is less. For general laboratory use, the following dimensions (outside measurements) have been found very satisfactory, but if desired the apparatus may be constructed with larger reservoirs to increase its capacity. DIMENSIONS OF LABORATORY GASSCRUBBER A Height of apparatus, om. Up er reservoir: &eight, om. Diameter om. volume (Aspacity), ml. Lower reservoir: Height om. Diameier om. VoluFe (ba aoity), m!. Cylindrical tuge connecting upper and tower reservoirs: Height om. Diameier om. Helical tub;: Length, em. Diameter om. Inlet jet, dikmeter of orifice, om. .4spiration rate, liters per hour
65
12 10
500
20 13 1000
25 3.5
VOL. 8,NO. 5
Absorption Vessel Apparatus B is a quantitative absorption vessel in which the absorbing solution is titrated directly, thus obviating the errors which inevitably occur when aliquots are removed for titration. This is an especially important consideration in titrating alkaline solutions to an alkaline end point. The gas to be determined is passed through the apparatus charged with the absorbing solution, which is then titrated by connecting the absorber to scrubber A as shown. The stream of carbon dioxide-free air effectively stirs the solution and circulates it in the absorber during titration, while a t the same time the countercurrent of air prevents carbon dioxide and other interfering atmospheric gases from diffusing into the vessel. Either compression or suction may be used to force the air through the system. If the latter is used, the tip of the buret is inserted through a rubber stopper (not shown) fitted into the tubulure at the top of the absorber. The dimensions (outside measurements) of the various parts of the apparatus are as follows: DIMENSIONS OF QUANTITATIVE ABSORPTIONVESSELB Height of apparatus, om. 60 Spiral tube: Reservoir : Length, cm. 180 Height, am. 11 Diameter, om. 0.6 Diameter om. 8 Inlet jet: Volume ohpacity, ml. 300 Diameter of lead-in tube, cm. 0.4-0.5 Vertical tube: Diameter of or!fice, om. 0.05 Length, om. 42 Aspiration rate, liters per hour 20-25 Diameter, om. 0.6 The aspiration rate given is for the aomplete absorption of COa in 0.1 N barium hydroxide solution. Obviously, the efficienoy of absor tion is dependent on the concentration of the absorbing solution as w e t as on the aspiration rate.
The principal advantages of the above absorber over most of those in general use are its efficiency in absorption, its small capacity for absorbing solution, and its design which permits direct titration of the absorbing solution without removing it from the vessel. Inasmuch as it will operate on as little as 30 ml. of liquid, relatively concentrated absorbing solutions may be used without requiring inconveniently large volumes of standard solution in titration. The importance of this feature has been discussed by Martin and Green (6) in their studies on the efficiency of absorption of carbon dioxide by barium hydroxide solutions of different concentrations. Although originally designed for the determination of carbon dioxide in respiration studies, it has been found highly satisfactory for the determination of free and combined ammonia by the aspiration method. The ease with which the absorbing solution may be titrated in the vessel makes it especially suitable for the determination of ammonia nitrogen in soils and similar material. Both gas-absorption vessels were made in a commercial glass-blowing laboratory operated by Mr. Greinke, Physics Department, University of Minnesota.
Literature Cited (1) Beaumont, J. H., Willaman, J. J., and De Long, W.A,, Plant Phz/siol., 2,487-95 (1927). (2) ENG.CEI~IM., Anal. Ed., 6, . . Cool, R. D.,and Graham, J. D., IND. 479 (1934). (3) Harvey, R. B., and Regeumbal, L. O., Plant Physiol.. 1, 205-6 (1926). (4) International Critical Tables, Vol. 1, pp. 67-8, 1926; Vol. 3, pp. 302-3, New York, MoGraw-Hill Book Co., 1928. (5) Kirk, P. L., Craig, R., and Rosenfels, R. S., IND. ENQ.CHEM., Anal. Ed., 6,154 (1934). (6) Martin, W. McK., and Green, J. R., IND. ENQ.CHEM., Anal. Ed., 5,114-18 (1933). (7) Milligan, L.H., IND. ENG.CHEM.,16,889(1924). (8) Weaver, E. R., and Edwards, J. D., Ibid., 7,534-5 (1915).
200
0.6 0.1 75
RECEIVEDJune 23, 1936. Contribution from the Department of Chemiatry, Montana Agricultural Experiment Station, as Paper 79,Journal Seriea.
