April 15, 1932
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
matter in the coal is not known to be less than 35 per cent. Longer periods of digestion (60 to 120 minutes) were employed in search of results indicating the loss of sulfuric acid by volatilization. This might be expected but was not found at the temperatures of the boiling 70 per cent perchloric acid (200” C.) under ordinary barometric pressures. (Compare analyses 21 and 22 with 19 and 20, as well as analyses 25 and 26 with 27 and 28.)
229
method of this paper, complete precipitation of the barium sulfate does not result (3). This error is not alone sufficient to account, except in part, for the low results obtained.
APPLICATION OF METHODTO ANALYSIS OF COKE The method as described was applied to the analysis of coke and gave very satisfactory comparisons in values obtained for some samples and very poor results for others. The disCOMPARISON OF ESCHRA AND PERCHLORIC ACIDMETHODS crepancies were not explained, and, until this can be done and the remedy found, the method is not recommended for sulfur A comparison of the Eschka and perchloric acid methods determinations in coke. for the determination of sulfur in coal is hardly justified on the basis of the present work when compared with the work of ACKNOWLEDGMENT
insoluble matter before barium sulfate is precipitated. This probably is a much more complete removal of silica from the solution before barium sulfateis precipitated than by the methods investigated by Selvig and Fieldner. Second, because of a comparatively high concentration of perchloric acid a t the time of precipitation of barium sulfate in the
LITERATURE CITED (1) SelVk and Fieldner, I N D . CHEM.9 19, 729 (1927). (2) Willard and Lake, J. Am. Chem. Soc., 42, 2208 (1920). (3) Wolesensky, ENG, 20, 1234 (1928).
cHEM.,
RECEIVED October 16, 1931.
Carbonate Content of Volumetric Sodium Hydroxide Solutions JOHN E. S. HANAND T. Y. CHAO,Y-1065CNorth Szechuen Road, Shanghai, China
T
The minute amount of carbonate present in tions were filtered through Jena HE best reagent quality lye??and sodium hydroside solutions treated sintered-glass crucibles, G4 (7). of s o d i u m h y d r o x i d e c o n t a i n s m o r e than 1 Filtration and siphoning were with various precipitants has been determined by per cent of sodium carbonate. carried out in absence of carbon various methods have been degravimetric and volumetric methods. Barium dioxide, vised for removing c a r b o n a t e hydroxide and salts were found to be the most MILK OF LIME (6) AND CAL from s o d i u m hydroxide soheffective precipitants. The technic of Warder’s CIUM CHLORIDE METHODS.Onemethod of differential titration has been improved hundred twenty-five grams of sotions intended for volumetric analysis. T h e s e m e t h o d s indium hydroxide were dissolved in and the results obtained checked within 0.02 per clude (1) precipitation with the water and made up to 2.7 liters. hydroxides or soluble salts of cent against the gravimetric evolution method. To this 300 cc. of milk of lime, the alkaline earths; (2) utilizing prepared from 20 grams of marthe small solubility of sodium carbonate in a concentrated ble lime, or 300 cc. of a solution containing 16 grams of calsolution of sodium hydroxide which is known as “oil lye” (14) ; cium chloride (dry neutral granules, Merck’s reagent) were (3) using metallic sodium with ether vapor as a barrier against added. The mixture was vigorously shaken for an hour and atmospheric carbon dioxide (3); and (4) employing an electro- allowed to settle for at least 4 days. lytically prepared sodium amalgam ( 1 , 5 ) . OIL LYE METHOD(14). Five hundred grams of sodium For general use, the precipitation and oil lye methods are hydroxide were dissolved in 500 cc. of water in a stoppered preferred for their simplicity and the ease with which large measuring cylinder of Jena glass. The total volume amounted quantities of solution can be prepared. The authors deter- to about 646 cc. A rubber stopper carrying a soda lime tube mined the small amounts of sodium carbonate remaining in and a siphon was fitted into the neck of the cylinder. The lye such solutions prepared under practical conditions, by both was clarified by heating near the boiling point of water (10) gravimetric and volumetric methods. in a specially constructed water bath for several hours, and cooled slowly. The water bath was provided with a false PREPARATION OF VOLUMETRIC SODIUMHYDROXIDE bottom and the measuring cylinder was completely enclosed SOLUTIONS except for the neck. Carbon dioxide-free water was used in all the experiments. For a normal solution, about 240 cc. of the oil lye from the The methods used for removing carbon dioxide from water, center of the container and sufficient water for diluting to 4.5 for storing and standardizing volumetric solutions, and for liters were siphoned into a 5-liter bottle without access of filling burets were the same as those described by Han and carbon dioxide, and mixed. METHODS USINGHYDROXIDES OR SALTS OF STRONTIUM AND Chu (4). The sodium hydroxide was of reagent quality (Merck’s pure), and a sample of it was found to contain 1.40 BARIUMAS PRECIPITANTS. For a 4 N stock solution (IS), per cent of sodium carbonate. All sodium hydroxide solu- 170 grams of sodium hydroxide were dissolved in water and
ANALYTICAL
230
EDITION
Vol. 4, No. 2
TABLEI. COMPARISON OF GRAVIMETRIC AND VOLUMETRIC METHODS VOLUMETRICNaOH SOLN.U S ~ D
GRAVIMETRIC METROD Carbonate in total Soh. No." Normality alkali Soh. No."
-
VOLVMETRICMETHOD --ACID INTO ALKALI Carbonate in Total Devn. Alkali from rav. Obsvd. C6r.b metgod 1
Normality
%
ALKALI INTO ACID Carbonate Devn. in total from grav. alkali method
%
%
%
Ca(0H)z siphoned
1
1.155
1.03 1.04 1.03 1.03
1
1.155
1.07 1.07 1.07 1.07
1.04 1.04 1.04 1.04
+0.01
0.56 0.66 0.76 0.66
-0.37
Ca(0H)z siphoned
2
1.024
1.09 1.07 1.08 1.08
2
1.024
1.12 1.12
+0.01
0.48 0.60 0.65 0.58
-0.50
0.00
+O.Ol
0.11 0.10 0.10 0.10
-0.04
$0.02
0.11 0.11 0.14 0.12
-0.01
0.03 0.02 0.01 0.02
+0.01
1.12
1.09 1.09 1.08 1.09
CaClz siphoned
3
0.9388
1.07 1.06 1.06 1.06
3
0.9388
1.09 1.09 1.08 1,09
1.06 1.06 1.05 1.06
Oil lye siphoned0
4
1.058
0.15 0.12 0.16 0.14
4
1.058
0.19 0.18 0.18 0.18
0.16 0.15 0.15 0.15
Oil lye filteredc
5
1.043
0.13 0.13 0.14 0.13
5
1.043
0.18 0.19 0.18 0.18
0.15 0.16 0.15 0.15
Sr(0H)z
6a
4.091
0.06 0.06 0.06
6b
1.114
0.08
0.08 0.08
0.00
1.11
0.08
0.06 0.06 0.06 0.06
9a
4.010
0.02 0.02 0.02 0.02
9b
0.8020
0.04 0.04 0.04 0.04
0.02 0.02 0.02 0.02
0.00
Ba(0H)r filtered
13a
4.103
0.01 0.01 0.01 0.01
13b
0.9965
0.03 0.04 0.03 0.03
0.01 0.02 0.01 0.01
0.00
BaCh siphoned
15a
4.305
0.01 0.01 0.01 0.01
15b
0.9493
0.04 0.04 0.03 0.04
0.02 0.02 0.01 0.02
I9a
3.756
0.01 19b 0.9109 0.01 0.01 0.01 Solution "b" was repsred by diluting solution "a" of the same number. For percentages &ve 0.10,correction is 0.03;for lower percentages, only 0.02. Solutions 4 and 5 were prepared from same oil lye.
0.03 0.04 0.04 0.04
0.01 0.02 0.02 0.02
0.06
SrCh siphoned
BaClz
0
b c
+ Ba(0H)z siphoned
mixed with a solution of the precipitant. The solution was 0' 1 liter and allowed to settle overnight. For a normal solution, 750 cc. of the clear stock solution were siphoned into a 4-liter flask and diluted to 3 liters. The solutions remained clear after dilution with an excess of precipitant present. For 1 liter of a 4 N solution, the following quantities of precipitants were used: Sr(OH)z.8H20, 9.8 grams; SrC12.6H20, 9.8 grams; Sr(NO,)z, 7.8 grams; Ba(OH)2.8H20, 11.6 grams; BaC12.2H20,9 grams; Ba(NO&, 9.6 grams. Strontium hydroxide was dissolved in boiling water, added to the sodium hydroxide solution, and the mixture shaken for some time. BARIUMNITRATEAND SODIUMSULFATEMETHOD. The details were the same as those described by Han and Chu (4). BARIUMCHLORIDE AND BARIUM HYDROXIDE METHOD(8). A normal sodium hydroxide solution previously treated with barium chloride and freed from barium carbonate was nearly saturated with barium hydroxide. GRAVIMETRIC ESTIMATION The apparatus used was an ordinary carbon dioxide train. The carbon dioxide liberated passed successively through concentrated sulfuric acid and phosphoric anhydride, and was absorbed in a Fleming bulb containing soda lime and phosphoric anhydride. Sulfuric acid was used for acidifying the sample. Where the sample was treated with a chloride in its preparation, a saturated solution of silver sulfate in 18 N sulfuric acid was used.fgr removing the traces of hydrogen chloride that happened to pass over. The air used for sweep-
+O.Ol
+O.Ol
ing the train was thoroughly washed by passing successively through two spiral wash bottles containing 28 per cent potassium hydroxide solution (16). VOLUMETRIC ESTIMATION Although accurate and reliable, the gravimetric method requires 200 to 700 cc. of sample and considerable time for each determination. A quick volumetric method is desirable, using 45 cc. of sample and giving results of comparable accuracy. For the volumetric analysis of hydroxide-carbonate mixtures, the method of Winkler is usually used. However, for the minute amount of carbonate left in a solution of sodium hydroxide after treatment with barium salt, this method is not suitable. Warder's method (16) is generally considered as being less accurate. Loss of carbon dioxide before the first end point and the hydrolysis of bicarbonate are the usual causes of error. Fortunately no difficulty is encountered when the amount of carbonate is small. The result for carbonate is seriously affected, however, by slight errors in the two end points. Thus, if 45 cc. of standard acid are used for the complete titration, and an error of 0.04 cc. of acid is made in each end point, the result for carbonate would be affected by 0.35 per cent when the errors are accumulative in nature. Rather (11) modified the original procedure of Warder by titrating nearly to t&firs.t end point with 2 N acid and finishing both with 0.2 N aejd. With this method of decimal end-point titration and o$her refinements in technic, the authors have been able to improve the precision to a remarkable degree. The results
April 15, 1932
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
obtained, after correction, checked the gravimetric method within 0.02 per cent. APPA~ATUS.A 50-cc. stopcock buret with a long nozzle was used for N hydrochloric acid. The nozzle was inserted through the central hole of a three-holed rubber stopper, whose two side holes carried a bent glass tube and a soda lime tube. During titration, the stopper was fitted into a 200-cc. Erlenmeyer flask of Jena glass, and a current of carbon dioxide-free air was passed into it through the bent glass tube without bubbling through the solution. The Erlenmeyer flask was thoroughly rinsed with carbon dioxide-free water immediately before use. The buret was flexibly supported from above, so that the Erlenmeyer flask could be rotated during titration. All burets were protected with soda lime tubes. MATERIALS.Hydrochloric acid, 1 N and 0.01 N : The normal solution was freed from carbon dioxide by boiling for 20 minutes and standardized against sodium carbonate. The 0.01 N solution was prepared by diluting the normal solution with carbon dioxide-free water. Sodium hydroxide, 0.01 N : A measured amount of oil lye was diluted and standardized against the 0.01 N hydrochloric acid. PROCEDURE. A plug of cotton wool was inserted into the neck of 8 200-cc. Erlenmeyer flask, and carbon dioxide-free air was passed through it, until the end of the analysis. Then 45 cc. of the 1N sodium hydroxide solution to be analyzed were introduced from a long-nozzle buret without removing the cotton plug. Two drops of phenolphthalein were added. The three-holed rubber stopper was immediately fitted into the flask, and 1 N hydrochloric acid, about 0.05 cc. less than that required for complete neutralization, was added very slowly. (The exact amount for complete neutralization was determined by a preliminary titration.) During the addition of acid, the flask was gently rotated to effect thorough mixing of its contents. The three-holed rubber stopper was removed from the flask and 0.01 N hydrochloric acid added until the faint pink color was just discharged as shown by comparison with water in a similar flask. A known amount of 0.01 N hydrochloric acid was added and the solution boiled for 15 minutes under a small reflux condenser with a current of carbon dioxide-free air slowly bubbling through it. A soda lime tube was fitted into the flask and the solution cooled with running water. The excess acid was titrated back with 0.01 N sodium hydroxide, and the faint pink color was finally discharged again with 0.01 N acid. The first end point was sharper when only small quantities of carbonate were present. The results obtained were expressed in terms of total alkali. 'Thus if 45 cc. of normal acid were used for the complete titration and 2.25 cc. of 0.01 N acid used for the second end point, then 0.10 per cent of the total alkali present was in the form of carbonate. COMPARISON OF RESULTS.Table I gives a comparison of the results by the two methods. The volumetric method gave slightly higher results than the gravimetric and the difference increased with the carbonate content of the sodium hydroxide solution. For percentages lower than 0.1, the correction was about 0.02, while for higher percentages of carbonate, it amounted to 0.03. Other results obtained by the volumetric method are shown in Table 11. The volumetric method is suitable for estimating the carbonate content of volumetric sodium hydroxide solutions, although with less than 0.03 per cent the accuracy is rather uncertain. REVERSEDTITRATION. Unreliable results are obtained if alkali is run into acid durine: u the titration.
231
TABLE11. VOLUMETRICESTIMATIONS SOLN. No.
1
NaOH SOLN.USED
NORMALITY
CARBONATE IN TOTAL ALKALI^
%
Ca 0H)z Ca lz CaL0H)a Oil lye Oil lye Sr(0H)r
1.155 1.024 0.9388 1.058 1.043 1.114
(1.04) (1.09) 1.06) 0.15) 10 0:06! 15
7
Sr(0H)z filtered
1.049
0.04 0.04 0.04 (0.02)
8
Sr(0H)z siphoned
1.116
0.03 0.03 0.04 (0.01)
9b
SrClz
0.8020
(0.02)
10
SrClz filtered
0.9955
0.05 0.04 0.04 (0.02)
11
Sr(N0a)a siphoned
0.9834
0.04 0.04 0.04
12
Sr(N0s)a siphoned
1.062
13b
Ba(0H)a filtered
0.9965
0.03 0.04 0.03 (0.01)
14
Ba(0H)a filtered
0.9457
0.04 0.04 0.04 (0.02)
15b
BaCla
0.9493
(0.02)
16
BaC12 siphoned
1.020
0.04 0.04 0.03 (0 * 02)
17
Ba(N0a)a siphoned
0.9434
' 0.02
Ba(N0a)a aiphoned
1.089
2 3 4 5 6b
(0.02)
0.04 0.04 0.04 (0.02)
18
0.02 0.03 (0.00)
19b
BaCIz f Ba(0H)z
0.9109
20
BaClz f Ba(0H)z filtered
1.092
21
Ba(N0a)z
22
23
4
+ NaaSOr siphoned
0.02 0.03 0.03 (0.01) (0.02) j
0.03 0.03 0.04 (0.01)
1.090
0.01 0.01 0.02 (0.00)
Ba(N0s)a f NazSOi (BaCOa filtered, Ba804 siphoned)
0.9803
0.02 0.02 0.02 (0.00)
Ba(N0a)z f NaaSOi siphoned
0.8845
0.02 0.03 0.08 ' (0.01)
Figures in parentheses are corrected average values.
COMPLETENESS OF CARBONATE REMOVAL The authors did not attempt to make a study of solubilities. The results presented show only the carbonate content of sodium hydroxide solutions treated and tested under practical conditions. Barium hydroxide and salts remove carbonate most completely and are to be recommended for general use. Although strontium carbonate is less soluble than barium carbonate (Q),yet strontium compounds were found to be less reliable for carbonate removal. Milk of lime does not remove carbonate so completely as compounds of strontium or barium, but
*
232
I
ANALYTICAL EDITION
it has the decided advantage of introducing the least amount of alkaline earth into the solution. The oil lye method has the advantage of requiring no precipitant. In a number of normal solutions prepared, 0.09 to 0.18 per cent of the total alkali was found to be present in the carbonate form, corresponding to 0.0048 to 0.0095 gram of actual sodium carbonate per 100 cc. Coles (2) obtained a 0.1 N solution of sodium hydroxide which gave no precipitate with barium hydroxide, by settling oil lye overnight and diluting a portion with freshly boiled water. Rising (18) prepared a similar 0.1 N solution by filtering oil lye and diluting with water which had been re-distilled over barium hydroxide, and found that the sodium carbonate content was about 0.0005 per cent. ACKNOWLEDGMENT The authors wish to acknowledge the valuable help received from I. M. Kolthoff and C. L. Shao in the preparation of the manuscript.
Vol. 4, No. 2
LITERATURE CITED (1) Clark, “The Determination of Hydrogen Ions,” p. 197, Wil(2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)
liams and Wilkins, 1928. Coles, J . Am. Chem. Soc., 30, 1192 (1908). Cornog, Ibid., 43, 2573-4 (1921). EN*. CHEM.,Anal. E d . , 3, 379 (1931). H a n and Chu, IND. Jorissen and Filippo, 2. angew. Chem., 23, 726-7 (1910); Chem. Weekblad, 6, 145-9 (1909). Kolthoff, Pharm. Weekblad, 58, 1413-17 (1921); 2. anal. Chem., 61, 48-51 (1922). Kolthoff-Furman, “Volumetric Analysis,” Vol. 11, p. 77, Wiley, 1929. Lunge, 2. angew. Chem., 11, 169-71 (1897). McCoy and Smith, J . A m . Chem. Soc., 33, 468-73 (1911). Pregl, 2. anal. Chem., 67, 23-7 (1925). R a t h e r , J . Am. Oflcial Agr. Chem., 1, 317-29 (1915). Rising, Svensk Farm. Tid.,16, 549-51; 566-8 (1913). Solvay Process Co., “Solvay Bulletin” No. A, sheet 8, 1925. Sorensen, Biochem. Z., 21, 186 (1909). Warder, J . Am. Chem. SOC.,3, 55 (1881). Wolf and Krause, Arch. Warmewirt., 10, 19-21 (1929).
RECEIVBD September 25, 1931. Presented before the annual convention of the Chinese Society of Science and Arts, Nanking, December 5 , 1930.
Composition of Vapors from Boiling Binary Solutions D. F. OTHMER,302 Seneca Parkway, Rochester, N. Y.
A
Vapor-composition curves, elevation of boiling The heating unit is formed by P R E V I O U S article (6) points of solutions, and related data on liquiditself before attachment to the described a m e t h o d and apparatus h a v i n g rest of the unit. It should be devapor systems necessary-for the design of engisigned to draw between and several advantages for the deneering equipment may be obtained conveniently 200 watts of power, Platinum termination of the composition of vapors arising from boiling and accurately with the apparatus and method and n i c h r o m e coils have been solutions of two volatile liquids. described. This work is a n imDrovement over used, and tungsten2would beuseSince this work was published, ful because of its low coefficient that previously published which lhas been used of thermal expansion which apthis system has been used by also, in obtaining various data. by several others proximatesthat of Pyrex,inmakthe writer and others in obt a i n i n g d a t a necessary for Several representative vapor-composition curves ing seals. Because of the high resistance of nichrome, a heater severaltypes of engineering are given. of this metal may be designed to problems, and various improvements have been made in the design of the glass apparatus. operate across an ordinary 110-volt circuit, but a platinumcoil unit should be designed to operate at a reduced voltage, APPARATUS USED The calculated length of wire is wound on a tube of Pyrex Figures 1 and 2 illustrate the apparatus’ used more recently previously pierced with two very small holes a t each end in studies of this nature. It is constructed of Pyrex glass, and of the length reserved for the coil. The ends of the wire it will be seen that, although several changes have been made, terminate in mercury wells attached to the sides for conthe same principles which governed the design previously used nection to the power supply. The lower end of the tube have been followed. An internal electric heater, incorporated carrying the heating coil is pierced with four holes about in the Kjeldahl flask which serves as the boiling pot, is the 5 mm. in diameter as close as possible to the inseal, so that largest single change, although the improved unit without no pocket is formed for liquid to remain undisturbed during the electric heater has been used as before, giving excellent the operation. OPERATION. When the flask is charged and current supresults with an external electric heater or a Bunsen flame. The unit is fabricated in one piece, being built around a plied, the bare wires lose their heat very readily to the surstandard Kjeldahl flask. This design is much simpler in rounding liquid. The vapor bubbles cause the boiling liquid construction, and offers several other advantages over the to rise around the coil, drawing fresh liquid down through the previous one which used a length of large-diameter glass tube, and through the holes a t the bottom. A cycle is made tubing. The methods and details of construction are ap: which ensures complete mixing throughout the liquid phase. parent by reference to the figures, and the changes from the Because of the very small bubbles formed in contact with the earlier model may be noted by comparison with the figure in fine wire, which is a t a temperature only slightly above the the previous article. If an external heat source is to be used boiling point of the solution, and the homogeneity of this rather than the internal one shown, the drain tube for sam- solution, this boiling is probably very nearly an “equilibrium ’ pling the boiling liquid is attached to the bottom of the flask at vaporization.” Vapor compositions have been determined from pressures a point opposite the inlet from the condensate reservoir, and supplied with a cock as before. 2 Tungsten wire may now be obtained from the Fansteel Co , Chicago, 1
The writer is prepared to supply directly orders for this apparatus.
111.
)
