July, 1919
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 SUMMARY
The inapplicability of the usual forms of gas-metering device t o the measurement of small rates of flow is discussed, and the resistance-tube flow meter, developed for this purpose in the Bureau of htines, is described. The nature of the flow of gas through these resistance tubes is considered from the point of view of flow meter design. Specifications for construction, calibration, and operation are included, and the in-
1
629
fluence of temperature and pressure changes discussed. This work was carried out under the direction of the Bureau of Mines. The writer wishes further t o express his deep appreciation of the valuable suggestions of Dr. E. Buckingham, of the U. S. Bureau of Standards. GAS MASKRESEARCH SECTION RESEARCH DIVISION,C W S , U. S. A AMERICAN UNIVERSITY EXPERIMENT STATION WASHINGTON, D. C. .
ORIGINAL PAPERS EQUILIBRIUM IN THE SYSTEM NapS04-CuS04-
HQSO4-HQ01 By H. W. FOOTE Received October 28, 1918
I n considering proposals for the utilization of niter cake, Johnston2 has stated t h a t “the best mode of using a solution of niter cake for any particular purpose could be ascertained from the appropriate solubility data; this involves the investigation * * * * of four-component systems such as Na2S04-HzS04FeSC)4-H20.” I t is hoped t h a t the present investigation may serve as an aid in t h a t direction. The problem has been limited t o determining t h e solubility relations] a t two temperatures, of the following systems: ( I ) NazSO4--H2SO~-HzO ( 2 ) CUSO~-H~SO~-HBO (3) NazS04--CuS04-H20 (4) N ~ Z S O ~ - C U S O ~ - - H ~ S O ~ - H ~ O A knowledge of ( I ) , (2), and (3) is obviously necessary in considering (4). Stated in a different way, the problem has consisted in determining the changes which take place when sulfuric acid, in increasing amounts, is added t o the system Na2S04-CuSO~-Hz0. S y s t e w containing more t h a n approximately 60 per cent of sulfuric acid in solution were not investigat ecl . I n general, only the solubility of univariant systems was determined and in plotting the results the points which represent them are connected b y straight lines t o show the composition of the corresponding divariant systems. Actually, these curves are usually somewhat concave. At a given temperature, the univariant systems of three components have two solid phases in equilibrium with a solution of fixed composition and vapor pressure. With four components, there are three solid phases a t such points. METHOD
To determine the univariant points in t h e threecomponent systems, a series of crystallization experiments a t t h e given temperature showed approximately the conditions necessary. The solution which deposited one compound near the point where another formed was then treated with an excess of the latter, or in some cases with both, and the solubility of the mixtiire determined. I n all cases, a second result 1 This investigation was undertaken at the request of the Division of Chemistry and Chemical Technology of the National Research Council. 2 THIS JOURNAL, 10 (1918), 468.
was obtained by adding further quantities of one or both solids and again shaking, the constancy of the results showing t h a t the univariant point had been reached. When the univariant points in the ternary systems had been fixed, i t was usually a simple matter t o obtain the corresponding points in the quaternary system by merely adding a n excess of the third solid necessary. Here also a duplicate result was obtained after adding further quantities of the solids in equilibrium. Solubilities were determined a t 12’ and 2 5 ’ . For 1 2 ’ a low temperature thermostat1 gave excellent service. A t 2 j o the ordinary form of thermostat, heated b y gas, was used. The various mixtures were shaken in glass-stoppered bottles, kept tight by dipping the tops in paraffin. Solutions for analysis were removed through small filters of glass wool directly into weighed specimen tubes. I n analyzing solutions containing all four components] copper was determined either electrolytically or, as the amount was always small, by precipitating as sulfide, roasting, and weighing copper oxide. After removing copper, sodium was determined in the filtrate as the sulfate, the excess of sulfuric acid being removed by ignition with ammonium carbonate. Free sulfuric acid was determined directly by titrating with standard sodium hydroxide. Preliminary determinations showed t h a t the small amount of copper sulfate present did not affect t h e end-point. I n a few cases, total sulfate was determined (by precipitating as barium sulfate) instead of weighing sodium sulfate, b u t the method was abandoned as less accurate t h a n the other. Where only three components were present, the method of analysis could be correspondingly simplified. (I) SYSTEM, N ~ ~ S O ~ - - H Z S O ~ - H ~ O This system has been investigated previously by D’Ans2 a t 2 5 O and by Pascal3 through a considerable range of temperature, though the latter expresses his results only in the form of a diagram which contains some obvious inaccuracies. D’Ans gives the solubility conditions for the following salts: Na2S04.1oH20, Na2S04, N ~ ~ H ( S O ~ ) ~ . H ZNOa ,~ H ( s 0 4 ) ~ , NaHS04.Hz0, NaHS04. The salt NaaH(S04)2.H20 forms spontaneously from solutions only very rarely and D’Ans speaks of ob12.physik Chem., 55 (1900), 749. 39 (1906), 1534; 2. unorg. Chem , 49 (1906), 356; 61 (1909). 91.
* Ber., a
Comfit. rend.. 164 (1917), 628.
630
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
taining i t only by chance, though when it has formed, i t can doubtless be obtained afterward by inoculating. I n all our experience we have never observed this form. I t s solubility relations, as shown by D'Ans, are very nearly those of the anhydrous form, so i t affects t h e diagram b u t slightly and i t is not considered here. It seems unlikely t h a t this form would be met in practice'. Our solubility results agree closely with those of D'Ans a t , z s 0 . One difference as t o the solid phases in strongly acid solution is mentioned later. The following results were obtained. Percentages here and in all tables following represent the parts in I O O parts of solution. The letters in the last column refer t o the corresponding points in the diagrams which are described later. TEMPERATURE = 12'
SOLIDPHASES NazSO4.10HzO. ........................
Corresponding Per cent Per cent Point HzS04 NazS04 in Diagram A None 9.53
__ 32.96 ~.
9 A4
......... 16.52 16.51 NaaH(S0i)a and NaHSO4.HzO.. .......... 27.96 27.96 NaH(SOa)z.HnO (Divariant)l.. ........... 58.79
32.90 25.38 25.45 4.33
TEMPERATURE = 25' NdzSO4.10HzO.. None NazS04.10H~Oand NazSOa. 8.62 8.62 NazSOa and NasH(SO4)z.. 16.25 16.29 NaaH(SO4)z and NaHS04.HzO 30.59
21 .901 33.46 33.50 35.20 35.53 27.13
NazSOa.lOHz0 and NaaH(S0a)z..
....................... ............. ............... ............zn (Divariant)z.. ............. 5 6 . 2 5
Q H
G
(3)
SYSTEM,
Vol. 11, N o . 7
NazS04-CuS04-HzO
This system has been investigated in some detail by Koppell and his data are given below for 2 5 " . A transition temperature in this system exists a t 1 6 . 7 ', below which only the single salts crystallize, while above i t the double salt NazSO4.CuSOd. ZHZOforms. At I Z ' , therefore, there is b u t one univariant system and the two solids present consist of the single salts. At 2 5 ' there are two such systems. I n one the solid phases consist of double salt and CuS04.gHz0, and i n the other, double salt and NazS04.1oHzO. TEMPERATURE = 12'
SOLIDPHASES NazSOa.lOHz0..
.....................
NazS04.10HzO and CuSO4.5HzO.. CuSOa3HzO..
Per cent NapSOa 9.53
......
.......................
9 54
10.43 10.44 None
TEMPERATURE = 25O NazS04.10HnO.. ..................... 21.90 NazSOa.lOHz0 and NszS04.CuS01.2HzO. 21.20 CuS04.5HzO and NazS04.CuS04.2HzO.. 10.95 CuS04.5HzO. ........................ None 1 J . A m . Chem. S o d . , 37 (1915), 288.
.
Corresponding Per cent Point CuSOi in Diagram None A 14.69 14.51 16.19 16.11
R
None 6.28 16.85 18.471
A
D
B
C
D
(4) S Y S T E M , NazS04-CuS04-HzS04-HzO
The general method of obtaining the univariant points in the four-component system has already I been mentioned. I n most cases there was no special H difficulty when once the univariant points in the q7 -9-6. -91 * NaHS04.HzO 6.54 G ternary systems were found. For each univariant point 1 Loewel, Ann. chim. phys., 131 49 (1857), 50. in the latter, there was a corresponding point in the 2 This was as far toward t h e sulfuric end of the diagram as we considered it necessary to go. D'Ans found a univariant point with theosolids quaternary system, in which the solution was saturated NaHSO4.HzO and NaHSOd a t about t h e same concentration a t 25 b u t a t neither 12' nor 25' did we get any indication of the second salt s't the with one more solid phase. For instance, starting concentrations given. The means we had of judging as t o the solid present here was t h a t a series of crystallizations carried out in this region all showed with the ternary univariant system containing t h e the very characteristic crystalline form of the hydrated salt. T h e solusolid phases CuS04.gHzO and CuS04.3H20, a unitions contained so much free sulfuric acid t h a t the crystals could not be freed from it properly and analysis could not decide which salt was present. variant point in the quaternary system could b e A salt very different in appearance, which was probably NaHSO4, was obtained in more concentrated solutions but its identity was not determined. reached by adding sodium sulfate. As this salt, howThe solubility relations are somewhat simpler a t ever, would be converted into the double salt Na2S04.1 2 " t h a n a t z;", for a t the former temperature the CuS04.zH20 before equilibrium was established, t h e anhydrous salt is no longer stable under any condi- latter was actually used in the solubility detCrminations, as D'Ans showed originally, and the decahy- tions. This double salt was the only one found a n d drate exists in equilibrium with the salt Na~H(S04)z exists under a very wide range of conditions. It forms one of the phases in every univariant system a t the univariant point. containing t h e four components. ( 2 ) S Y S T E M , CuS04-HzS04-Hz0 The relations in the system a t 1 2 " are unusual in I n this system no acid salt forms, but the presence one respect. As already mentioned, the two salts of sulfuric acid dehydrates the pentahydrate in stages, in water do not form a double salt a t this temperayielding the trihydrate, monohydrate, and ultimately ture, but crystallize separately. With more t h a n the anhydrous salt in strong sulfuric acid. A dis- 7 . 4 per cent of sulfuric acid, the double salt forms, a n d cussion of this behavior will be found in a previous a t this concentration of acid there is a univariant. article' from which t h e solubility results a t 2 5 " have system with the three solid phases, CuS04.gH~0, been taken. Bell a n d Taber2 have also determined NazSOd.IoHzO, and double salt. The presence of t h e Following are the sulfuric acid causes the double salt t o be stable below the solubility of this system a t z 5 ', results : its transition temperature. The case is comparable TEMPERATURE = 12O Corresponding with the simpler one of sodium sulfate, in which t h e Per cent Per cent Point C U S O ~ inDiagram anhydrous form may exist in contact with sulfuric SOLIDPHASES &SO4 None CuSO4.5HzO.. ....................... 16.11 16.19 D acid solutions below its transition temperature into CuS04.5Hz0 and CuSOa.3HzO.. . . . . . . . . 5 1.63 1.67 E the decahydrate, but I a m not aware of any similar 51.38 1.61 CuSOa.3HzO and CuS04.HzO ........... 61.56 0.87 F case which has been observed with four components. 61.52 0.75 The solubility d a t a for the univariant systems are TEMPERATURE = 25' 18.47 D given in the following table. The one divariant system CuS04.5Hz0. ........................ None CuSO4.5HzO and CuS04.3Hz0.. . . . . . . . . 49.20 2.83 2.13 F E included a t each temperature shows the limiting CuSOa.3HzO and CuSOa.Hz0 ........... 55.72 value obtained on the curve a t the sulfuric acid end, 1 J . A m . Chem. SOC.,37 (1915), 288. A
J
I-.".
-
2
J . Phys. Chem., 12 (1908), 171.
12.phys.
Chem., 42 (1902), 1.
.
.July, 1919
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY TEMPERATURE = 12'
Per cent HzSOa SOLIDPHASES NazS04.10Hz0, NasH(SOa)z, D S ' . . . . . . 16.50 16.54 -hTaaH(SOa)z, NaHSO4.Hz0, D.S.. ...... 27.97 27.86 NaHSOa.Hz0, D.S. (Divariant) 58.20 50.41 CnSO.i.5Hz0, CuS04.3Hz0, D.S........ 50.54 CuS04.3Hz0, CuSOa.H?O, D.S.. ....... 59.96 59.86 7.40 NazSOa.lOHz0, CuS04.5Hz0, D.S.. 7.42 TEMPERATURE = 25' NazSOa.lOHz0, Na&Oa, D.Sl. ......... 8.58 8.59 NazSO,, NaaH(S032, D.S. . . . . . . . . . . . . 16.21 16.18 .NaaH(SOd)z, NaHSOcHzO, D.S........ 30.41 30.52 NaHSOa.Hz0, D.S. (Divariant). . . ;. 55.58 55.46 CuSO4.5He0, CuSOa.3Hz0, D.S.. ...... 47.04 47.11 ,CuSOa,3HnO, CuSOa.Hz0, D.S.. 54.15 53.80 1 Double salt. ~
.......
....
631
Corre-
Per sponding Per cent cent Pointin NalSOi CuSOa Diagram 32.92 0.18 0.13 32.89 0.08 25.47 0.14 25.36 4.65 0.77 1.60 2.53 1.59 2.51 2.59 0.73 2.80 0.73 13.62 8.65 8.82 13.69
..
.......
33.18 33.43 35.57 36.16 26.98 27.02 6.62 6.54 2.98 2.81 2.38 2.63
0.44 0.44 0.18
0.19 0.16 0.20 0.69 0.87 2.75 2.97 2.24 2.10
K
L M N
P
V
Equilibrium in the system CuS 04.5 H20- X a& 0 4 . I o H ~ O , D. S. given in the above table a t 1 2 O was -reached very slowly and it is possible for the two single salts t o remain in contact with a solution con-taining considerably more than 7 . 4 per cent of sulfuric acid and show no sign of transforming into double :salt even after a considerable time. The other syst e m s offered no difficulty in reaching equilibrium. F
FIG.2-TEMPERATURE = 2.5'
systems are, of course, limited by these three-component curves, the points inside, a t the intersection of three curves, representing univariant systems with three solid phases; the lines, divariant systems with two solids; and the fields, trivariant, with one solid. The fields, and their corresponding solid phases, are as follows: 1 2 O (Fig. 1) NazS01.CuS04.2HzO.. N MS T P V I NazSO4.1OH%O............. A Q S T R NazSO4.. .................. Absent NanH(S0a)z.. .............. Q H M S NaHSOcHzO..: ........... G H M N1 CuSOaSHzO.. D E PTR CuSOa.3HzO.. ............. E F V P 1 Field incomplete a t sulfuric acid end.
......
.............
-
FIG. I-TEMPERATURE1 2 O
The relations of the different systems appear much clearer when the results which have been given are plotted. This has been done in Figs. I and 2 . The percentages of sodium sulfate, copper sulfate, and sulfuric acid are plotted respectively on the three axes, OA, OD and 0 2 , which make an angle of I Z O O with each other. For clearness, the scale for sulfuric acid is one-half t h a t for the two salts. Points where the same solids are present a t both temperatures are lettered alike. AQHG a t 1 2 ' (Fig. I ) and AJIHG a t 2 5 ' (Fig. 2 ) represent the solubility of sodium sulfate in sulfuric acid solutions; D E F gives that of copper sulfate a t both temperatures, and DRA a t I z O and ABCD at z j O give the solubility of sodium and copper sulfates (or their double sulfate) in water i n the presence of each other. The four-component
25O (Firr. 2 ) N M L K B-C P VI A J K B
i LLKL
GHMN' D E P C
EFVP
The diagram shows the wide range of conditions under which the double salt forms and t h e extremely limited range of stability of the acid sulfates of sodium in the presence of dissolved copper sulfate, which converts them into the double salt. The very slight solubility of copper sulfate on the sodium sulfate-sulfuric acid side of the diagram is of course shown quantitatively in the solubility tables. Some of the difficulties which have been met in using niter cake t o replace sulfuric acid for pickling copper alloys are probably due to this slight solubility, which causes the double salt to precipitate. The slight solubility also points t o an obvious way of preventing copper sulfate from accumulating in solution or of removing it from solution. Sodium sulfate forms double salts with all the vitriols, which resemble each other markedly in general solubility relations and in the fact t h a t they are formed from their components above the transition temperature and break down below, this being the reverse of the common behavior of double salts. The transition temperatures also all lie near each other. On account of these similarities, it is probable that the system which has been investigated is typical of systems containing other vitriols in place of copper sulfate. SHEPPIELD CHEMICAL LABORATORY YALE UNIVERSITY NEW HAVEN,CONNECTICUT
