Feb., 1920
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
TABLEI1 SOLUTION A ' SOLUTION B Amount of CO already Amount of CO already absorbed.. . . . . . . . . . . . 0 . 0 cc. absorbed.. . . . . . . . . . . . 0 . 0 cc. Volume of gas taken.. 5 0 . 0 cc. Volume of gas taken.. ... 5 0 . 0 cc. Time Amt. CO Time Arnt. CO Min. Absorbed Min. Absorbed 1 47.4 1 48 0 2 2 0.4 0.6 3 0.2 3 0.4
THE DETERMINATION OF OXYGEN BY THE COPPERAMMONIA-AMMONIUM CHLORIDE REAGENT
...
Amount of CO already absorbed.,. . . . . . . . . . 433.2 cc. Volume of gas taken.. 5 0 . 0 cc. Time Amt. CO Min. Absorbed
..
1
47.8
2 3
0.0
'
..........
..
2 3
0.6
Amount of CO already absorbed. . . . . . . . . . . . 9 12.4 cc. Volume of gas taken,. . . 5 0 . 0 cc. Time Arnt. CO Min. Absorbed I 2 3
Amount of CO already absorbed.. 433.6 cc. Volume of gas taken.. 5 0 . 0 cc. Time Amt. CO Min. Absorbed 1 48.0 0.2 0.0
Amount of CO already absorbed.. . . . . . . . . . . 912.4 cc. Volume of gas taken 5 0 . 0 cc. TimeAmt. C O Min. Absorbed
47.4 0.4 0.4
...
1
2 3
47.6 0.2 0.4
R. P. Anderson1 states t h a t t h e rapidity with which a solution absorbs a relatively pure gas is much greater t h a n t h a t with which i t absorbs a gas from a mixture. This fact undoubtedly explains why Solutions A and B seem t o be more efficient after renewal. The gas which was run into the renewed solutions was more nearly pure carbon monoxide than the gas used with the fresh solutions, and hence the greater speed with which the second sample of gas was absorbed. Since this second series of tests was otherwise run under practically the same conditions as in the first series, i t is evident t h a t solutions of cuprous chloride which have been saturated with carbon monoxide may be renewed b y driving off the carbon monoxide by heating, and the solution made as efficient for the absorption of carbon monoxide as i t was originally. CONCLUSIONS
I-The presence of stannic and stannous chlorides, even in relatively large amounts, in a hydrochloric acid solution of cuprous chloride, does not impair the efficiency of the solution for the absorption of carbon monoxide. 11-A practical and efficient method for the preparation of a solution of cuprous chloride for absorbing carbon monoxide consists in dissolving cupric chloride in concentrated hydrochloric acid and reducing t o cuprous chloride by the addition of stannous chloride. If a slight excess of stannous chloride is added the solution may be transferred from one container t o another and the pipette filled without oxidation of the cuprous chloride. 111--A hydrochloric acid solution of cuprous chloride, when saturated with carbon monoxide, may be renewed b y heating t o 60' and 70° C. t o drive off t h e carbon monoxide. A solution treated in this manner will be as efficient for the absorption of carbon monoxide as i t was originally, and if in renewing t h e solution in this way a small amount of the copper is oxidized, and the solution is not colorless, a few drops of a concentrated stannous chloride solution will again reduce it. 1
THISJOURNAL, 7 (191.9, 587.
161
By W. L. Badger CHEMICAL ENGINEERING LABORATORY, UNIVERSITY OF MICHIQAN, ANN ARBOR, MICHIGAN Received June 26, 1919
Hempell described a reagent for the determination of oxygen which consists of spirals of metallic copper covered with a solution which consists of a mixture of equal parts of saturated ammonium carbonate solution and ammonia of specific gravity 0.93. He states t h a t such a solution has a vapor tension which may be neglected in most cases, and t h a t i t will absorb twentyfour times its volume of oxygen. Dennis2 repeats Hempel's account of this reagent practically word for word. No investigation seems t o have been made since Hempel's original statement. I t seemed t o the writer t h a t a different concentration of reagent might be desirable, and t h a t other ammonium salts might be substituted for the carbonate. I n determining the capacity of this reagent, the conception of Anderson3 of the specific absorption of a gas reagent was followed. The reagent was used t o determine oxygen in air, and attempts were made t o determine the point a t which this reagent no longer gave quantitative results on air after 5 minutes' shaking. All the analyses were made over water and the value of 20.9 per cent oxygen was adopted with a n allowable error of *O.I per cent. The apparatus employed is illustrated in Fig. I . A and B form a standard Hempel pipette for solid reagents. The additional bulb C and the leveling bulb D were filled with mercury which acted as a seal t o prevent access of oxygen t o the reagent. E is a Hempel burette modified4 by attaching a three-way stopcock t o the top instead of the ordinary two-way stopcock. The manipulation was as follows: The bulb A was filled with spirals of clean copper wire, and the whole apparatus was flushed out with nitrogen. A definite quantity of the solution t o be investigated was introduced through Stopcock I . This was forced over into A and up into the capillary just t o Stopcock 2 . By means of t h e funnel and Stopcock 3 , the whole of the apparatus between Stopcocks 2 and 4 was filled with water. I n the burette was measured a 100-cc. sample of air, and in passing i t over into A the water in the capillary connections was forced out through the third way of Stopcock 2 , thus preventing any dilution of the reagent. With the three-way stopcocks as shown, the volume of the capillary was entirely eliminated and, therefore, a capillary of rather large bore was used, making the manipulation more rapid. The sample of air was shaken for 5 min. with the reagent, and on returning it t o the burette, the reagent was allowed t o rise in the capillary only up t o Stopcock 2 . Water was then introduced through the third way of Stopcock 2 t o finish flushing the gas through the capillary connection into the burette. 1 2 8
4
"Gasanalytische Methoden," 1900 Edition, p. 142. "Gas Analysis," 1913, p. 166. THISJOURNAL, 7 (1915), 575. White and Campbell, J . A m . Chem. Soc., 37 (1905), 734.
.THE J O U R N A L O F I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
162
E
L
FIQ.1
Since the capacity of the reagent for oxygen proved t o be so large t h a t i t would require many hundreds of samples of air, a large receiver filled with commercial oxygen was substituted a t intervals for the burette E and 500 or 1000 cc. a t a time introduced into A. TABLEI-HEMPEL'S SOLUTION Equal parts NHaOH, sp. gr. 0.93,and saturated (NHa)sCOa soh.,220 cc. Oxygen Taken cc. 20.9 20.7 20.9 20.8 20.8 20.8 2069.0 20.3 20.7 20.7 20.7 20.7 20.5 20.9 20.5 98.8 20.3 98.4 20.9 98.2 20.7 97.6 99.2 20.9 20.7 98.0 20.3 98.0 20.9 196.6 20.5 292.6 20.6 185.5 20.7 20.6
Total Oxygen in Soh. cc. 20.9 41.6 , 62.5 83.3
104.1 124.9 2193.9 2214.2 2234.9 2255.6 2276.3 2297. O 2317.5 2338.4 2358.9 2457.9 2478.0 2576.4 2597.3 2695.5 2716.2 2813.8 2913.0 2933.9 2954.6 3052.6 3072.9 3170.9 3191.8 3388.4 3408.9 3701.5 3722.1 3907.6 3928.3 3848.9
Oxygen in Air Per cent 19.0 20.3 21 .o
Carbon Dioxide cc. 1.5
Ammonia c c.
... ...
1.4
20.7 20.8
1 .o 2.5 1.6 1.6 1.5
17.4 20.0 20.5 20.2 20.7 20.6 20.6 20.4
2.2 0.8 0.3 0.0 0.6 0.7 0.6 0.2
0.2 0.0 0.0 0.0 0.5 0.2 0.0 0.0
20.4
0.2
0.0
...
...
... ...
20.8
...
20.6
... ...
20.7 20.3
... ...
20.5 20.8
... ... 20.9 ... 19.8
20.8
19.9
...
...
... 0.1 ... 0.2
... ... ... 0.0
0.2 0.1
... 0.3 ...
0.0
... .. .. ..
...
...
... 0.3 ... 0.0 ... ... 0.7 0.1 ... 0.4 ... 0.1 ... 0.7
0.8
... ... 0.1
0.0
... ... 0.7
0.8
0.0
Vol.
12,
No.
2
The residual impurities were, of course, measured and allowed for in the calculations. Oxygen was thus introduced and, a t frequent intervals, analyses of air made until the reagent either became so foul t h a t the gas could no longer be handled quantitatively or until i t failed t o give 20.9 per cent in 5 min. The first reagent experimented with was the one described by Hempel, namely, a mixture of one p a r t of a saturated solution of commercial ammonium carbonate with one part of ammonia, sp. gr. 0.93. This reagent seldom gave 20.9 per cent of oxygen in air. It was found necessary t o treat the nitrogen returned t o burette E after a n analysis, first with a caustic solution t o remove the carbon dioxide, and then with a dilute sulfuric acid solution t o remove the ammonia. The amount of ammonia reported b y this manipulation naturally varied since considerable ammonia was dissolved by the burette water, and consequently the amount reported depends upon the rapidity of manipulation. Table I gives the results with the Hempel solution. I t is evident t h a t this solution will not give satisfactory results for the determination of oxygen. Various ammonium salts were investigated, b u t preliminary experiments showed t h a t ammonium chloride would possess the largest capacity and give the most satisfactory results. The following solutions were investigated: SOLUTION I-Concentrated ammonia, sp. gr. 0.90, saturated with ammonium chloride (see Table 11). It is evident t h a t this reagent is exhausted a t about 5500 cc. of oxygen, giving a specific absorption of about 2 2.5 volumes. Oxygen Taken cc. 20.9 20.8 10.5
10.4 10.4 968.2 20.9 20.9
10.4 970.9 10.6 10.9 971.2 18.2 20.9 16.7 968.1 16.7 16.7 16.7 16.8 483.7 16.7 16.7 481.9 16.9 15.5 481.8 16.3 16.3 16.6 483.9 16.7 16.5 16.6 480.8 16.5 16.7 17.0 16.9 483.4 16.1 16.7
TABLE11-200 Cc. OB SOLUTION 1 Total Oxygen Oxygen in Soh. in Air Ammonia Per cent cc. REMARKS cc. 20.9 20.9 7.8 41.7 20.8 30.5 52.2 21.0 3.4 62.6 20.8 2.6 73.0 20.8 8.4 1041.2 2i:o 1062.1 20.9 18.3 1083.0 20.8 2.0 1093.4 2064.3 20:8 2074.9 4.6 2085.8 20.9 3057.0 20:9 ;:6 3075.2 2.4 20.9 3096.1 5.6 3112.8 20.9 At about 3600 cc. of oxygen a 4080.9 precipitate of cuprous oxide began t o form 4097.6 20.9 7.3 4114.3 20.9 3.4 4131.0 21 .o 3.6 4.0 4147.8 20.9 4631.5 26:9 0:7 4648.2 20.9 4664.9 0.4 5146.8 26:9 5163.7 4.0 20.9 5180.2 5662.0 20:s 1:6 5678.3 1.6 20.5 5678.3 3.2 5694.9 20.7 Solution absorbs oxygen more 6178.8 rapidly after standing over night 6195.5 20.9 3.3 20.7 5.6 6212.0 20.8 5.6 6228.6 6709.4 20:4 1:9 6725.9 6742.6 3.8 20.5 10 min. 3.2 21.0 6759.6 4.8 10 min. 20.9 6776.5 7259.9 26:2 1:9 7276.0 10 min. 20.9 3.3 7279.7
1:7
i:s
..
..
2:5
..
..
Feb., 1920
T H E J 0 L ; R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
SOLUTION 2-Two parts concentrated ammonia, one part water, the mixture saturated with ammonium chloride (see Table 111). The limit in this particular case is about 9500 cc. of oxygen, although this is not due t o a failure t o react b u t t o t h e precipitate slowing down the reaction until it takes longer than t h e 5 min. arbitrarily set. This would give a specific absorption of 45 t o 47 volumes.
Oxygen Taken cc.
TABLE 111-200 CC. O F Total Oxygen Oxygen in S o h . in Air Ammonia Cc. Per cent Cc. 20.9 1.0 20.8 1.4
975.2 20.9 977.5 978.0 20.9
6903.9 6924.8 7902.3 8880.0 8901.2
977.0 20.9 20.9
9878.2 9898.4 9919.3
4.8
2Q:9
2.8
20:9
1.8
...
...
., , .. .. ., . ..
7 min. for absorption 6.5 min. 6 min. precipitate began form 7 min.
.. .. ..
20 min.
2019
..
0.5
2019
0.2
20:2 20.9
REMARKS
...
20:9
.. .. ..
2
SOLUTION
to
12 min.
...
Copper heavily precipitate 35 min.
...
10 min.
0.2
coated
with
3-One part concentrated ammonia, one part water, t h e mixture saturated with ammonium chloride (see Table IV). The limit of this reagent came a t t h e point where t h e precipitate was so bulky as t o clog t h e capillaries or entrap bubbles of oxygen in t h e pipette. Otherwise t h e reaction was still quantitative. The limit is somewhere between 11000 and 1 2 0 0 0 cc. of oxygen, giving a specific absorption of 5 5 t o 60 volumes. TABLEIV-200 Oxygen Taken cc. 965.6 21.0 964.8 20.9 965.2 20.9 966.1 20.9 977.5 20.9 977.7 20.9 977.3 20.9 978.0 21.0 977.0 20.9 977.0 20.9 978.0 20.9 964.0 20.9
CC.
O F SOLUTION
Total Oxygen Oxygen in S o h . in Air Ammonia Cc. Per cent Cc. 965.6 986.6 2i:o 3.8 1951.4 ... 1972.3 20:9 3.0 2937.5 ... 2958.4 1.9 2619 3924.5 ... 3945.4 1.6 20:9 4922.9 ... ..
7919.6
8916.6 8937.5 9914.5 9935.4 10913.4 10934.3 11898.3 11919.2
974.7
4895.1
..
20.9 975.0
4916.0 5891.0
20.9
20.9 974.5 20.9 20.9
5911.9 6886.4 6906.6 6927.5
20.9
None
20:9 I 20.5 120.9
Node None
Oxygen in Air Ammonia Per cent Cc.
..
20:9
..
..
*.
... Node ., .... ...
None
...
REMARKS 30 min. 12 min. 10 min. 8 min. precipitate began to form
lo--min. precipitate heavy; trouble capillary
very with
14 min. copper heavily coated and solution foaming badly 25 min.
5 min. shaking 10 min. shaking
6 . 5 min.
8 . 5 min. 12 min.
CONCLUSION
15 min.
I-The solution of ammonia and ammonium carbonate recommended by Hempel and copied by Dennis is not a satisfactory reagent for oxygen. 11-The most convenient solution is made by saturating with ammonium chloride a mixture of one part concentrated ammonia and one part water. This solution will absorb from fifty t o sixty times its volume of oxygen, and then fails, not by refusing t o absorb quantitatively, but by the formation of so heavy a precipitate t h a t i t becomes unmanageable. The reagent is still useful for a considerable time after t h e precipitate begins to form. 111-The advantages of this reagent are: t h a t i t is cleaner t o use and has a longer life than pyrogallate;
20:9
0.1
26:9
Oxygen Taken cc. 975.0 974.8 20.9 974.9 974.8
SOLUTION 4
... 0.1 ...
1.6
2i:o
OF
...
20.9
20:9
3
Cc
Total Oxygen in S o h cc. 975.0 1949.8 1970.7 2945.6 3920.4
I n the analysis of commercial oxygen, where t h e residue of unabsorbed gas is very small, care must be taken that one or two copper wires project clear up into t h e entrance t o the capillary; for if t h b g a s residue is not in contact with metallic copper, the last traces of oxygen will not be absorbed. I t would seem, then, t h a t the mechanism of the reaction is t h a t t h e copper is first oxidized, and t h e ftmction of t h e solution is simply t o dissolve this oxide, leaving fresh and active copper surfaces for further oxidation.
...
4943.8 5921.5 ’ 5942.4 5919.7 6940.6 7918.6
are fairly reliable because, by this time, so many analyses had been run t h a t the manipulation was very uniform. I n spite of t h e fact t h a t during the earlier part of its use considerable quantities of ammonia are liberated, it would seem t h a t Solution 3 represents t h e most desirable composition. Some tests have been made which indicated t h a t in these solutions, after considerable copper has been dissolved, the absorption of acetylene is as rapid and as complete as the absorption of oxygen; and much more rapid than any of the other reagents for acetylene noted in the literature. Systematic investigation of this point has not been made. Van Brunt1 says t h a t in t h e use of this reagent, a considerable amount of oxygen is absorbed by t h e cuprous salts in solution. The present set of experiments and some four years’ experience with this reagent in large classes in gas analysis have shown t h a t this is not true. Even with reagents containing large amounts of cuprous salt in solution, if t h e copper in t h e absorption pipette falls below the surface of the liquid, absorption of oxygen almost completely stops. TAWEV-2b0
SOLUTION
163
None None
26:9
ik’;dne
26:9
ik’dne
26:9
Nine
REMARKS 18 min. 12 min. 10 min. 10 min. 10 min. precipitate beginning t o form on coils
8 . 5 min.
35 min. 45 min. Precipitate very heavy on coils and in solution. At this point capillary became clogged
S O L U T I O N 4-One part of concentrated ammonia, two parts water, t h e mixture saturated with ammonium chloride (see Table V). Here the limit was somewhere above 6000 cc. of oxygen, giving a specific absorption of 30 volumes. The figures in Tables I1 t o V showing t h e amount of ammonia given off were determined by passing the gas residue left after the analysis of air into a sulfuric acid pipette and noting t h e decrease. These figures
1
J . Am. Chem. S o t , 36 (1914), 144.
164
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
i t is free from the danger and the influence of catalyzers which interfere with phosphorus; i t is readily prepared from common reagents; and i t is active a t almost any temperature. IV-Its disadvantages are t h a t it cannot be used on gas mixtures which contain either carbon monoxide or acetylene; and when fresh, it leaves measurable amounts of ammonia in the gas. This last may be remedied by keeping the burette water slightly acid. ACKNOWLEDGMENT
The writer wishes t o express his appreciation of the work of Mr. Wyatt A. Miller, who made the analyses on Hempel's solution, and t o Mr. E. 0. Scott, who did all the rest of the analytical work.
EQUILIBRIA IN SOLUTIONS CONTAINING MIXTURES OF SALTS. 11-THE SYSTEM WATER AND THE CHLORIDES AND SULFATES OF SODIUM AND MAGNESIUM AT 25' By Walter C. Blasdale DEPARTMENT OF CHEMISTRY, UNIVERSITY BERKELEY, CAL.
OF CALIFORNIA,
Received June 6, 1919 INTRODUCTION
The equilibria which exist in aqueous solutions containing chlorides and sulfates of sodium and magnesium were discussed by Hildebrand' who prepared the phase-rule diagram representing the system a t 25' based upon data from a number of sources, but owing t o the incompleteness of these data two of the important points on his diagram were conjecttiral only. I n attempting t o ascertain by actual experiment the location of these points it became evident t h a t some of the results used in the preparation of the diagram were incorrect, and since the diagram is of immediate importance in discussing methods for the recovery of magnesium salts from bittern and from the waters of certain lakes, it was thought desirable t o redetermine all the data needed for the construction of the complete diagram. I n carrying out the experimental work needed to obtain these d a t a I have received much valuable assistance from Miss Carolyn Steel.
Vol.
12.
No.
2
equilibrium with each of the eight solid phases. Since the system can be expressed in terms of three components, and since a liquid phase is always assumed t o be present and the pressure is constant, i t would be impossible to prepare solutions which are in equilibrium with more t h a n three of these solids simultaneously, unless the transition temperature had been chosen fortuitously, in which case four solids might be present. I n ascertaining the limits of the eight fields the following procedure was adopted: First, the compositions of solutions saturated with respect t o the four simple salts MgS04.7Hz0, N ~ ~ S O ~ . I O H Z MgC12.6H~0 O, and NaCl were determined, and the ends of the two axes already referred t o were fixed. Second, the solubility of each of these four salts in solutions containing increasing concentrations of a second salt which yielded a common ion, and, therefore, contained three ions, was determined up t o the point a t which a second solid phase appeared; this fixed a number of points lying between the extremities of the two axes representing solutions in equilibrium with two solid phases. Third, starting with solutions saturated with respect t o two solids, the composition of solutions saturated with respect t o each pair of solids in the presence of increasing concentrations of t h a t salt which yielded a fourth ion was ascertained up t o the point a t which a third solid was separated.
EXPERIMENTAL METHODS U S E D
This system forms a reciprocal salt pair, which can be represented graphically b y reference t o two axes intersecting a t right angles, provided the concentrations are expressed in double equivalents per unit weight of water, t h a t is, by using one axis t o represent the relative proportions of MgS04 and NazClz, and the other of Na2S04and MgC12. The previous work FIG I-TRE SYSTEM MgSOrNaCl AT 25' on the subject indicates t h a t the solid phases t o be expected a t this temperature are MgS04.7Hz0, MgS04.This procedure made i t possible t o check each step 6 H z 0 , MgS04.Hz0, NazSOe.IoHzO, Na2S04, MgC12.- in the process of establishing the critical points of t h e 6Hz0, NaCl and the double sulfate MgS04.Na2S04.- diagram, and gave more detailed information regard4H20known as astracanite. The problem presented ing the exact form of the different fields t h a n is usually was t o determine the limits of the fields representing shown on similar diagrams. The details of procedure the composition of all the solutions which can be in adopted in carrying out the solubility determinations differed in no essential respect from those used in similar 1 THISJOURNAL, 10 (1918), 9 6 .
