Carbonate Content of Oil Lye Clarified by Centrifugation and Long Settling JOHN E. S. HAN, Shanghai, China
T
The carbonate content of the siphoned lye was slightly higher than that of the filtered lye; on an average they amounted to 0.11 and 0.10 per cent, respectively. Neither the siphoned nor filtered lye was perfectly clear, because of the presence of minute quantities of solid particles which had passed through. (The carbonate contents were slightly lower than the average value of oil lye clarified by heating, which also became slightly turbid on cooling.) The author also examined a number of long-settled oil lyes; some had been settled for 1 to 5 months, and others for 2 to 2.5 years. Their carbonate contents seem to depend primarily on the temperature a t which they were settled. Lyes 1 to 5 months old, which were settled and siphoned ( o r f i l t e r e d ) a t temperatures not higher than 18" C., contained 0.07 per cent of carbonate, while three lots of lyes 2 to 2.5 years old all contained 0.09 per cent. The lyes 2 to 2.5 years old had been settled for much longer periods and were siphoned or filtered at temperatures not higher than 19" C., but they had passed two successive summers (with maximum temperature of 38" C.) in contact with solid sodium carbonate. Apparently the redissolved sodium carbonate formed supersaturated solutions. Experimental data for the centriFIQURE1 fuged lyes and settled lyes 4 to 5
HE small amount of carbonate remaining in volumetric sodium hydroxide solutions after different treatments'
for carbonate removal has been determined by Han and Chao (3). Although the "oil lye" method does not remove carbonate as completely as precipitation with barium salts, yet it has the decided advantage of not introducing foreign ions into the solution. The long time required for the solid carbonate to settle out is sometimes a disadvantage. Han and Chao found that when settling was hastened by heating as recommended by Pregl (4, the oil l y ~ contained 0.09 to 0.19 per cent of carbonate. (The carbonate content was expressed in terms of total alkali. Thus on an average 0.15 per cent of the NazO present was in the form of Na2C03.) Allen and Low ( I ) shortened the time of settling by centrifuging oil lye at 2200 to 2300 r. p. m. for 30 minutes. Their data were obtained by a volumetric procedure somewhat different from that of the author and were not checked against a standard method. The centrifuge method, however, has a distinct advantage over that of Pregl in not requiring heating which might increase the solubility of sodium carbonate. The author considered it worthwhile to redetermine the carbonate content of centrifuged oil lye by both gravimetric and volumetric methods. The author prepared oil lye by dissolving sodium hydroxide (reagent quality) in an equal weight of water, allowing it to cool, and centrifuging four 250-cc. portions in closed tubes at 2000 to 2300 r. p. m. for 30 minutes. The lye became perfectly clear and most of the solid matter acked tightly on the bottom of the tubes. A small amount o?solid matter, however, remained floating on the surface of the lye and could be easily disturbed on the introduction of a siphon. For volumetric analysis the simplified procedure of the author (9)was used. An Erlenmeyer flask was freed from carbon dioxide, filled with oil lye, and attached to the buret as shown in Figure 1. The buret was filled with N hydrochloric acid in the absence of carbon dioxide. No titration head was used, as entry of carbon dioxide was prevented by soda-lime guard tubes.
TABLEI. COMPARISON OF GRAVIMETRIC AND VOLUMETRIC METHODS Volumetrio Method
Gravimetric Method Oil Lye Useda Na@ in form coz Total of oarbonate VOl. found Na,O Uram Gram Uram % cc. 25.66 0.0193 0.0272 0.11 46 46 26.66 0.0194 0.0273 0.11 c
Description of Oil Lye Frsshly prepared oil. 1 e, cooled to centrifuged, and sipxoned
a
b 0
17O
c.,
..
...
....
....
Freshly prepared oil lye cooled to 17O C., centrifuged, and filterid through Jena 61ter tube ( G 3 )
90 90 90
51.18 61.18 51.18
0.0370 0.0372 0.0370
0.0621 0.0624 0.0621
Settled for 5 months, siphoned
90 90 90
61.42 51.42 61.42
0.0264 0.0266 0.0272
0.0372 0.0376 0.0383
Settled for 4 months, filtered through Jena filter crucible 1G3
90 90 90
60.69 60.59 60.69
0.0266 0.0260 0.0246
0.0361 0.0352 0.0347
Settled for 4 months, filtered through Jena filter cruoible 1Q4
90 90 90
52.23 62.23 52.23
0.0245 0.0242 0.0248
0.0346 0.0341 0.0349
(0.h 0.10 0.10 0.10 (0.10) 0.07 0.07 0.07 (0.07) 0.07 0.07 0.07 (0.07) 0.07 0.07 0.07 0.07)
NazO in Form of Carbonate 1st End Point 2nd End Point Direct 0.9983 0.02066 0.02066 0.02618 calcula-Correoted N HCI N ECI N €IC1 N NaOH tion (-0.02) Cc. 0.64 0.76 0.86
Cc. 2.10 1.88 2.38
%
%
42.80 42.80 42.81
0.67 0.28 0.84
0.124 0.129 0.131
42.68 42.68 42.68
0.80 0.84 0.48
1.88 2.38 1.62
0.50 0.94 0.32
0.123 0.119 0.119
41.90: 41.90 41.900
0.52 0.90 0.60
2.02 1.84 1.54
0.84 0.74 0.48
0.096 0.090 0.092
41.220 41.220 41.220
0.64 0.33 0.46
1.64 1.42 1.47
0.60 0.40 0.42
0.091 0.091 0.094
0.10 0.11 0.11 (0.11) 0.10 0.10 0.10 (0.10) 0.08 0.07 0.07 (0.07) 0.07 0.07 0.07 (0.07)
42 66C 42.560 42.660
0.68 0.16
1.14 1.29 1.64
0.08 0.28 0.38
0.099 0,090 0.102
Cc.
Original oil.lye without dilution, prepared by dissolvin sodium hydr0xid.e in an equal weight of water. 46 oe. of orlginal oil lye diluted to 871 CC. and 46 cc. ofthe solutlon obtrwned used for each titration. !.022 N.
Figures ID parentheses are averaged vdues.
140
0.48
Cc.
0.0s
0.07 0.08 (0.OS)
MARCH 15, 1937
ANALYTICAL EDITION
months old are given in Table I. All filtrations were carried out by gravity, without suction and without access of carbon dioxide. Pressure was obtained by maintaining a fairly high column of lye over the filtering medium. and Oil 1J7e can be in paraffinlined bottles until needed. Preference should be given to the centrifuge method rather than the heating method, when oil lye must be clarified in a short time. The author is indebted to K. F. Tseng and M. I. Okada
141
for permission to use the laboratories of the Shanghai Scienm Institute for part of the experiments.
Literature Cited (1) (2) (3) (4)
Allen and Low, IN=.EN^. CHEM.,Anal. Ed,, 5, 192 (1933). H ~Ibid,, ~ 6,, 2~~ (1934). H a n a n d Chao, Ibid., 4,229 (1932). Pregl, 2.anal. Chcm., 67,23-7 (1925).
R B C ~ I V ENovember D IO, 1936.
Anhydrous Sodium Carbonate as a Standard of Reference in Acidimetry J
Stability of Sodium Carbonate in the Temperature Range 300' to 400" C. G. FREDERICK SMITH AND G. F. CROAD, University of Illinois, Urbana, Ill.
THE
generally accepted procedure for the preparation of anhydrous sodium carbonate by the conversion of pure sodium bicarbonate calls for decomposition a t 300" C. Waldbauer, McCann, and Tuleen (3) state that this conversion can be carried out a t temperatures from 102Oto450' C. The wide difference between the previously accepted maximum temperature of 300' C. and the findings of Waldbauer and collaborators (3)has led to the present investigation.
Preparation of Materials
APPROXIMATELY 0.2 N HYDROCHLORIC ACID. Portions of constant-boiling hydrochloric acid were weighed from weight burets, transferred to calibrated volumetric flasks, and diluted to volume.
Experimental Procedure The purity of the anhydrous sodium carbonate was first experimentally demonstrated. Weighed portions of anhydrous sodium carbonate (corrected to the vacuum bash) were weighed into 400-ml. beakers, dissolved in water, and titrated, using the standard hydrochloric acid and Bureau of Standards calibrated burets. The agreement between the calculated normality of hydrochloric acid and the values found by this method, assuming the anhydrous sodium carbonate to be pure, is indicated by the following series of results:
CONSTANT-BOILING HYDROCHLORIC ACID. This was made by the rocess described by Foulk and Hollingsworth ( I ) , and the distihion flask and condenser as well as the pressure-regulating apparatus were exact duplicates of those which they described. Since but two fractions of distilled acid were desired, the receiver was modified as shown in Figure 1. By its use the first 400 ml. of distillate were collected with the receiver in position as shown in Figure 1. The last portion of distillate, 50 ml. of constant0.2320 0.2320 0.2322 0.2319 Av. 0.2320 (calcd. 0.2318 boiling acid, was collected in the smaller of the two receivers 0.2006 0.2003 0.2000 0.2002 Av. 0.2002 (odd.O.ZW2] after the receiving flasks had been inverted without discontinuing the process of distillation. The constant-boiling hydrochloric The results show an agreement t o Within less than 0.01 per acid was taken at 750-mm. pressure, after correcting the existing cent of theory, and are typical of results obtained from 10 barometric reading with the pressure-regulating system as different solutions of standard hydrochloric acid from differshown. A 5000-ml. flask was placed between the acid receiver from the still and the pressure-regulating device to minimize ent samples of prepared constant-boiling acid. The indicator fluctuations in the water manometer shown. Ten grams of used in these titrations was an aqueous solution of 0.10 per platinum scrap were used in the distilling flask to prevent bumpcent methyl orange and 0.25 per cent indigo carmine. The ing, the distillate was collected at a rate of 4 to 5 ml. per minute color change is from green in basic solution to gray a t the end as recommended, and 50 ml. of undistilled acid were left in the still. ANHYDROUSSODIUM CARp o i n t a n d violet in acid BONATE. Pure sodium bicarsolution. It is concluded bonate was dissolved in pure that the anhydrous sodium water t o make a saturated carbonate was pure as presolution at 80' C., which was filtered and allowed t o cool. pared. The sodium bicarbonate thus obtained was centrifuged and Change in Alkaline dried at approximately 50 C . Qualitative tests showed the Value absence of chloride, sulfate, potassium, etc. Anhydrous Samples of the same prepasodium carbonate was preration of anhydrous sopared from the bicarbonate dium carbonate were heated by the process described by for 4 hours a t various temSmith and Hardy ( 2 ) . The sodium bicarbonate was disperatures between 300' and sociated at 290" c. at 1- to 390" C. and used to stand4-mm. pressure d u r i n g a ardize a given solution of period of 1 hour and stored standard hydrochloric acid in glass-stoppered bottles in a desiccator over a n h y d r o u s made from constant-boiling magnesium perchlorate. The material as described. apparatus assembly for this The results, s h o w n in preparation is shown in FigFIGURE1. APPARATUS FOR PREPARATION OF CONSTANTTable I, are averages from at BOILINGHYDROCHLORIC ACID ure 2.
