I-1-D GSTRIAL A N D ENGINEERI,VG CHEMISTRY
October, 1926
1069
Apparatus for the Direct Determination of Carbon Dioxide' By J. E. Underwood RESEARCH DEP.ARTMEST, %T.ATIOSAL LIMEASSOCI.%TIOh-, 918 G S T . ,
HE determination of carbon dioxide in limestone and lime products may be carried out by either of two general methods applicable to carbonates. The more rapid and less accurate method depends upon the loss of weight which results when a carbonate is decomposed by a strong acid or other means. ?rIany different forms of apparatus have been devised for use in this process and the results obtained are sufficiently accurate for ordinary control purposes. I n the other general method the carbon dioxide evolved by the decomposition is purified and led into a suitable absorbing agent contained in an apparatus of such form that it may be detached and weighed. The purification of the gas requires a number of separate units in the form of a continuous train. Each unit contains some reagent rvhich must function effectively in removing any contaminating gases. Accurate results are obtained, but inasmuch as all parts of the train must be swept clean of carbon dioxide, this method requires a longer time. I n order to gain the desired accuracy of this second method and also to reduce the period of time for the determination, an apparatus has been devised as is shonn in the accompanying drawing.
T
Apparatus and Procedure
The manipulation procedure varies little from that eniployed in using the ordinary train. [-sua1 prerautions are taken to sweep out the apparatus with carbon dioxide-free air before the determination is started. The weighed sample in powdered form is boiled with hydrochloric acid. (In case of quicklime or hydrated lime, a catch sample should be made from a weighing bottle pro9
A
N.\V.,\VASHISGTOK. D.
C.
After introduction into tube A the sample is covered with water and the tube is attached to the apparatus. The previously weighed absorption bulb H is attached to G. Hydrochloric acid contained in separatory funnel B is allowed to flow into tube il until B is empty, the rate being governed by the rate of evolution of gas. The original amount of hydrochloric acid must be previously regulated so that the level of the contents of A is not above P. A current of carbon dioxide-free air is started through the apparatus and the contents of A brought to the boiling point. The form of A allows the gases generated to be quickly and effectively swept out. Water has been placed in tube C to point P ' . The gases from d enter the water in C in very small bubbles. Although the contents are heated by the steam, practically no acid progresses beyond bulb C. The gases containing the carbon dioxide then pass through D, which is filled with mossy zinc. This not only acts as a condenser but also removes any hydrochloric acid passing C The microdrier E is analogous to C, the water being replaced with concentrated sulfuric acid. The issuing gas from E passes through small bulb G containing phosphorus pentoxide, which eliininates the possibility of residual moisture or entrained sulfuric acid entering the absorption bulb. Although any carbon dioxide absorption apparatus may be used, an ordinary Midvale bulb, H , is found satisfactory when iiscarite2 is used as the absorbent. To preclude the loss of the moisture produced in the absorbing reaction, the gases are also passed through a layer of phosphorus pentoxide which is separated from the Ascarite by glass wool. The Ascarite and dehydrating agent are consequently weighed together. I n preparing this bulb a layer of glass wool, extending aboi-e the end of the outlet tube, is placed in the bottom, and on this a layer of phosphorus pentoxide from 6 to 10 mm. in thickness. Immediately above is another layer of glass wool, and the rest of the bulb is filled with Ascarite, except for a final layer of glass wool a t the top to distribute the incoming gas evenly over the cross section of the bulb. When the sample evolves hydrogen sulfide in the treatment with hydrochloric acid, another bulb exactly like E is interposed between D and E . This bulb contains a solution of cadmium chloride, which removes the hydrogen sulfide without disturbing the progress of the carbon dioxide. Tube C gradually fills by condensation. This condensate is eliminated and fresh water again added by means of stopcock I. Frequently, a t the same time, the train is disconnected between bulbs D and E and the former is also flushed out. Stopcock I1 may also be utilized in emptying and refilling E. Comparative Results
n d e d with a ground stopper.) The hydrochloric acid and water vapor are eliminated and the purified carhon dioxide is absorbed by any suitable absorbent. The apparatus containing the absorbent is disconnected and weighed. Provision may be made for the elimination of hydrogen sulfide if this is also generated with the carbon dioxide.
' Received
June 7, 1925
The following results were obtained using a standard argillaceous limestone from the Bureau of Standards, averaging 30.68 per cent COS. W'eight of sample Grams 1,4274 0.4223 0.3iZ2 0.3245 0,2925 2
COn found Per cent 30 78 30.i9
30 78 30.80 30 80 ;2verage 3 0 . 7 9
Stetser and S o r t o n , I r o n .Age. 102, 443 (1918).
I N D L'STRIAL -4SD EATGI,VEERING C H E J f I S T R Y
1070
The results of analysis of two different hydrated limes are as follows: OESERVED DATA-Hydrate A Hydrate B
r
Weight of sample Grams
cot
Weight sampleof Grams
COZ Per cent
0.97 0.92 0.94 0.95 0.97 0.95 0.95
2.4331 2.4950 2.7554 2.7381
0.75
Per cent
3.2633 3.i 8 4 9 2.8334
3.5343
3.1645 3.7234
Average
0.79 0.81
0.81 0.19
BUREAU OF STANDARDS FIGURES
*
H y dCO? rate H5'$6f Per cent Per cent
0.97 0.96 0.93 0.91 0.97 0.90 0.94
0.83 0.80 0.78 0.85 0.80 0.75 0.80
Vol. 18, No. 10
Advantages of the Apparatus
1-Accurate and consistent results are obtained with very small amounts of carbon dioxide. 2-The contaminating gases are removed quickly and efficiently and carbon dioxide is not retained except in the absorbent. 3-Those materials in the train units which need to be frequently replaced are in solution form, and new material may be easily substitut'ed. 4--The total volume of the apparatus is small making for rapidity of determination.
The Absorption of Gases in Milk of Lime' Part I By H. C. Weber and K. T. Nilsson DEPARTMENT O F CHEMICAI,
EWIS and Whitman*
ENGINEERING, hIASSACHUS8lTS
L
is assumed that there is a film of comparatively stationary gas on the gas side and of comparatively stationary liquid on the liquid side of the interface. The assumption is made that there are no convection currents in these films and that the transfer of matter takes place entirely by diffusion. It must be evident that there is a rapid change in concentration through these films and that the rate of transfer of matter is proportional to the driving force (concentration difference), to the cross section, and inversely proportional t o the film t,hickness. I t is often assumed, for the sake of simplification, that substantial equilibrium exists between the gas and the liquid a t the interface. This furnishes another equation for the determination of the film coefficients, as the equilibrium concentrations in the gas and liquid are generally known. The rate of absorption of highly soluble gases is governed by the gas-film resistance, while the liquid film is the controlling factor for slightly soluble gases. Rapid motion of the fluid-as, for instance, stirring-decreases the film thickness. The rate of diffusion through the film is a function of the viscosity. The effect of temperature on absorption and on film resistance has already been pointed out by Haslam, Hershey, and Kean.3 It is known that as the molecular weight of the solute increases its diffusivity decreases, but the decrease in diffusivit'y is usually small compared with the increase in molecular weight. Note-The diffusion of electrolytes in the presence of other electrolytes is a complicated case t o handle quantitatively.4 The rate of diffusion of an ion is dependent on its mobility, but since the ions of an electrolyte are oppositely charged their rates are not independent of each other. Krdusj gives the following equation for the rate of diffusion:
2uv u
TECHNOLOGY, CAMBRIDGE, MASS.
An apparatus has been constructed for determining the conditions governing the absorption Of gases in milk of lime solutions. The present article gives the results obtained by absorbing practically pure carbon dioxide in various lime solutions under conditions of constant temperature. The results have been interpreted by a consideration of the multiple-film theory of absorption.
have d e v e l o p e d t h e two-film theory for the absorption of gases in liquids. This theory applied to experimental and data has proved most useful in the study of absorption. ~t
D=-
INSTITUTE OF
+ I'
RT
1 Presented at the 8th Annual Convention of the h'ational Lime Association, French Lick, Ind , June 10, 1926. 1 THISJOURNAL, 16, 1215 (1924). 8 Ibid., 16, 1224 (1924).
while it is 4.67 i n a solution ammonium chloride.
0.52
where
and
are the ionic mobili.
ties, R is the gas constant, and T the absolute temperature. This equation holds fairly well
Ee~ : e e , t ~ ~ ~ ckt ~ t e ~ ~ is still more complicated where we have a mixture of two or more electrolytes. Thus the diffusion coefficient for 0.52 N hydrochloric acid in water a t 12' C. is 2.09, N in hydrochloric acid and 3.43 N in
The results obtained in this investigation will be interpreted on the basis of t,he multiple-film theory developed by Lewis and Whitman. Apparatus and Procedure
A round Pyrex flask was set up in a constant-temperature bath (Figure 1). This flask contained a stirring device and an outlet tube, both of which were sealed with mercury. Carbon dioxide gas from a cylinder was admitted to a copper coil a t 2. From here the gas passed through a scrubbing bottle filled with water, through a second copper coil, and then through a second scrubbing bottle containing water, then on to a flowmeter containing a thermometer where both temperature and rate of flow of the gas were determined. The wash bottles and the coils were placed in a separate constant-temperature bath so regulated that saturated carbon dioxide gas was delivered to the flowmeter a t the same temperature as was being maintained in the main thermostat (28.5" C.). Before making a run the water pump, P , was started and water from the thermostat was circulated through the measuring buret, B. The hydrate of lime was prepared by adding the required quantity of oxide to somewhat less than 300 cc. of boiling distilled mater. The solution was kept bofiing for 3 minutes and then allowed to cool, after which the volume was made up to 290 cc. This solution was transferred to flask A and the whole apparatus with the exception of the gas buret was flushed out with carbon dioxide a t 28.5" C. for 3 minutes flowing a t the rate of 4 liters per minute. During this time the stirrer was not running. A threeway stopcock a t the bottom of the buret made it possible 4 Haskell, P h y s . R e v . , 27, 145 (19081. 6
Kraus, "The Properties of Electrically Conducting Systems," 1922,
p. 282.
