IhTDUSTRIAL A N D ENGINEERING CHEMISTRY
January 15, 1929
an indicator. A definite amount of the indicator-for example, 0.5 ec. of 0.02 per cent solution, the reaction of which has been adjusted to approximate neutrality-is added to the solution before titration and the end point determined by matching with the faint pink color of a standard solution. This titration is very readily carried out and the end point is extremely permanent and sensitive, 0.1 cc. of 0.002 N alkali being sufficient to cause a definite color change. A blank titration must also be made. Table I-Sulfur Dioxide in Mixtures of Sulfur Dioxide a n d Air a s Indicated by Hydrogen Peroxide a n d Iodine Methods
sox CONCENTRATION
DIFFERENCE BETWEEN CONDUCTIVITY METHOD AND: TION METHOD
ConducAcid tivity titration Iodine ~
1
1 1 1 1 6 15 20 20 6 15 8 12 4
--
0.37 0.39 0.40 0.69 0.93 0.35 1.36 1.71 3.19 6.41 13.58 24.1 36.4 58.3
0.35 0.37 0.41 0.71 0.90 0.30
...
1.61 2.90 6.40 13.55 24.3 37.2 59.1
0.38 0.38 0.39 0.69 0.88 0.35 1.44 1.75 3.24 6.43 13.40 24.4 35.0 56.4
Average
Maximum
0.05
0.10
0: i7
0: 40
0.30 0.07 0.20 0.2 0.8 0.8
0.50 0.10 0.50 0.3 1.7 1.2
I
second absorber placed in series with the first having indicated that this amount of gas escaped absorption. At 15 p. p. m. less than 1 per cent of the gas reached a second absorber. Advantages of New Method The new method has several advantages over the iodine method. The solutions are easier to prepare and the absorption is as rapid and complete as with the iodine method. It is not necessary to adjust the strength of the oxidant to correspond to the particular concentrations of sulfur dioxide with which it is desired to work. The data give the amount of gas absorbed directly and not indirectly through the decrease in concentration of another constituent of the system.
IODINE METHOD
Measurement of Both SOz a n d SOs
Aver- Maxiage mum
0.00 0.07 0.04 0.06 0.14 0.27 0.3 1.4 1.9
0.03 0.10 0.09 0.10 0.25 0.5 0.7 2.2 2.7
Comparison of Methods The new method has been checked against the iodine method, previously described, by analyzing uniform gas mixtures simultaneously with both procedures. The results are given in Table I and ,show a satisfactory concordance over a range from less than 0.4 p. p. m. to 60 p. p. m. The five single det,erminations represent large samples of gas, 120 t o 200 liters; the other values are the mean of a number of consecutive analyses of a uniform gas mixture carried out according to the regular procedure. At the highest concentrations the results are probably low to the extent of 2.5 per cent, a
15
If it is desired to measure both sulfur dioxide and sulfur trioxide in a gas mixture, the two methods could be conveniently applied to this end-the iodine method to measure the sulfur dioxide and the hydrogen peroxide to measure the total acidity. As a general rule, however, the amount of sulfur trioxide is inappreciable compared with the sulfur dioxide, and can be neglected. Application in the Field The method can doubtless be applied to the problem of the continuous measurement of the concentration of sulfur dioxide in the field. Only slight modifications would be necessary to permit the apparatus to operate for 1 or 2 days without any attention. The period of sampling could conveniently be increased to about 10 to 20 minutes since concentrations greater than 5 p. p. m. would seldom be encountered. The final adjustment of the carbon dioxide equilibrium, which is always accomplished in less than half a minute, would then have a negligible effect on the results. It would also be desirable to have a record of the gas volumes and liquid volumes, even though these values are constant. A thermograph and barograph would complete the necessary equipment to permit the calculation of the sulfur dioxide concentrations.
Continuous Laboratory Extractor for Liquids' Alfred W. Francis ARTHUR D. LITTLE,INC., CAMBRIDGE, MASS.
ONTINUOUS extractors for liquids with volatile immiscible solvents have been described in the literature,2 but most of them'require either elaborate glass blowing, or else, since fairly large volumes of solution are used, the extraction is very slow. A simple apparatus was devised for the analytical extraction of liquids. Two forms are illustrated ( A ) for solvents lighter than the extracted solution, and ( B )for heavy solvents. Each is made from a pipet of any desired size with the stems bent and connections sealed, as shown. In ( A ) the bulb of the pipet is filled four-fifths full with glass beads before bending the upper stem. The bulb in ( B ) can be filled completely afterwards. The sample, about half the capacity of the bulb, is pipetted into the bulb, before the solvent in ( A ) and after it in ( B ) . Enough solvent is used to fill the rest of the bulb and tubes and have 20 to 30 cc. in the receiving flask. The solvent is distilled by means of a hot plate through the upper tube which is bent downward to avoid excessive r d u x condensation. After dropping back from the condenser, the solvent bubbles through the
C
1 Received November 9, 1928. * Fiske, A m . Chem. J., 41, 510 (1909): Berlin, German Patent 251,459 (June 24, 1911), see C. A., 7 , 7 (1913);Watkins, IND. ENG. CHEM.,il, 612 (1925).
sample in the bulb, up in ( A ) or down in ( B ) ,and overflows back into the receiver. If the extract can be titrated directly, as in the case of acetic acid, it is convenient to provide a buret and follow the extraction as it proceeds. This permits extrapolation to infinite time with great accuracy. An extraction of acetic acid from 50 cc. of salt solution with ether removed half the total in 8 minutes, half the remainder in the next 8 minutes, etc., so that in an hour the extraction was practically complete.
b-----d A
