ANALYTICAL CHEMISTRY
1144 made in a darkened room using a narrow beam of light falling on a thin layer of the soap solution. It has been possible to obtain results indicating the amount of residual detergent present in various systems such as latices, textile dips, emulsions, and colored soap solutions under these experimental conditions. For example, the use of changes in dye fluorescence to determine th'e total area of polymer particles and, from this, particle diameters was found to. give results in agreement with those diameters determined by light scattering (9). Similarly, determinations of total areas of polymer particles using conductivity, surface tension, .and changw in dye spectra resulted in polymer particle diameters which were in good agreement with those calculated from electron microscopic data on the same samples 1 I ). LITERATURE CITED
(1) Corrin, M. L.,Klevens, H. R., and Harkins, R. D.. J . Chem. Phys., 14,206,480(1946). (2) DuBois, A. S.,Soap Sanit. Chemicals,22, 125 (1946). (3) Hartley, G. S., "Aqueous Solutions of Paraffin-Chain Salts," Paris, Hermann e t Cie, 1936.
(4) Hartley, G. S., and Runnicles, D. F., Proc. Roy. Soc. (London), 168A,420 (1938). (3) Hoffpauir, C. L., and Kettering, J. H., Am. Dyestufl Reptr., 35, 265 (1946). (6) Klevens, H. B., J . Am. Oil Chemists' Soc., 26,456 (1949). (7) Klevens, H. B.,J . Chem. Phys., 14,742 (1946). (8)Ibid.,17,1004 (1949);J. Am. Chem. SOC.(in press). ' (9) Klevens, H. B.,J . Colloid Sei., 2,301, 365 (1947). (10) Klevens, H.B.,J . Phys. Colloid C h a . (in press). (11) Klevens, H. B., unpublished data. (12) Lambert, J. M.,J . Colloid Sci., 2,479 (1947). (13) Lingafelter, E. C., Wheeler, 0. L., and Tartar, H. V., J . Am. Chem. SOC.68, 1490 (1946). (14) hlarron, T. V.,and Schifferli, T., IND.ENG.CHEM.,ANAL.ED., 18, 49 (1946). (15) Merrill, R. C.,and Getty, R., J . Phys. Colloid Chem., 52, 774 (1948). (16)Preston, J. M.,J . Soc. Dgers Colourists, 61,165 (1945). (17) Ralston, A. W., and Eggenberger, D. N., J . A m . Chem. Soc., 70, 983 (1948). (18) Sheppard, S. E., and Geddes, A. L., J . Chem. Phys., 13, 63 (1945). RECEIVED November 10, 1949.
Determination of Chlorine in Silicate Rocks PAUL K. KURODA
AND
E. B. SANDELL, U n i v e r s i t y of M i n n e s o t a , M i n n e a p o l i s , M i n n .
A suitable photometric method for the determination of small amounts of chlorine in silicate rocks may be based on the formation of a colloidal suspension of silver sulfide by treatment of the ammoniacal solution of isolated silver chloride with sulfide.
-
T
HE method commonly used for determining total chlorine in silicate rocks involves precipitation as silver chloride and weighing as such after sodium carbonate fusion of the sample. Although the gravimetric method gives satisfactory results with higher chlorine contents if a double precipitation is made (Table I ) it is not very suitable for the small amounts (usually less than 0.05%) ordinarily encountered in the common igneous rocks, when results of the greatest accuracy are desired. Moreover, the gravimetric method is inadequate when the amount of sample is limited, as when chloripe is to be determined in the component minerals of a rock. For geochemical studies it is desirable to have available a method that will allow the determination of a few hundredths of 1%of chlorine in a 0.1-gram sample within 0.005%. Two methods for the determination of small amounts of chlorine were investigated. The first was based on the potentiometric titration of chloride with silver nitrate solution to the equivalence potential existing under the conditions, as empirically determined. Although this method was not studied as fully as desirable, it appeared to be a feasible one. 'However, it seemed to offer no advantages over the second method studied, in which silver chloride is precipitated with an excess of silver nitrate, the washed precipitate is dissolved in ammonium hydroxide, and silver in the solution is then determined photometrically with sodium sulfide as reagent (yellow-brown coloration). The determination of silver, and indirectly of chloride, with sulfide as photometric reagent is an old procedure, but it has been applied more in biochemical than in inorganic analysis. I n ammoniacal medium a stable silver sulfide sol is obtained, and in the authors' experience it is not necessary to use a protective colloid when the silver concentration is less than 0.1 mg. per milliliter. The solution appears clear as long as this limit is not esceeded, and no appreciable change in optical density is shown on long standing (Table 11). The relation between silver concentration and extinction is linear up to 100 p.p.m. of silver when a suitable filter is used. The use of potassium dithio-bxalate and thioacetamide as reagents in place of sulfide was investigated, but they were found to
have no general advantages. These substances furnish sulfide ion by hydrolysis and give colloidal suspensions of silver sulfide. Dithio-oxalate behaves practically the same as sulfide, the only difference being that clear sols can be obtained a t higher silver concentrations than in the case of sulfide, Thioacetamide produces turbid solutions unless the silver concentration is less than 25 to 30 p.p.m., but the optical density is almost twice that which is obtained with sulfide or dithio-oxalate as reagent. Results obtained by the proposed sulfide method according to the directions given in the procedure following are listed in Table 111. It is believed that in the ,majority of cases, the error in the determination of 0.01 to 0.02 and 0.05% of chlorine will not exceed 20 and 10% relative, respectively, when a 0.5-gram sample is taken. Even with a 0.1-gram sample the error will not be much greater than this if the volume a t the time of precipitation is
Table I.
Gravimetric Determination of Chlorine in Silicate Rocks" Sample
Diabase
Chlorine Presentb, %
0,020
0.033 0.070 0.125 0.185 0.26 0.51
Chlorine Found, %Single pptn. Double pptn.
0.03 0.04-t 0.08f 0.14 0.21 0.28 0.50
..
o:07
.. 0:26d
0.51
0.5-gram sample fused p i t h 2.5 grams of NapCOa. AgC1 precipitated from 100.ml.of solution containtng 0.5 ml. of 1 t o 1 HNOi in excess. b Sum of chlorine originally present and t h a t added. C Silver chloride precipitate dissolved in 2 ml. of 1 t o 1 ",OH, solution diluted to 10 ml.. and slight excess nitric acid added. d Refusion of residue from leach of first sodium carbonate melt showed 3% of total chlorine remaining in this residue. a
V O L U M E 2 2 , NO. 9, S E P T E M B E R 1 9 5 0 reduced proportionately for the smaller sample. The volume of the final solution in which the silver sulfide sol is developed is maintained constant a t 10 ml. independent of the sample size, so that the photometric error may become significant when a 0.1gram sample is taken. Under the authors' conditions, 1 p.p.m. of silver in solution gives an extinction (log l o l l ) of approximately 0.003 in a 1-cm. cell. Inasmuch as 1p.p.m. of silver is equivalent to about 0.3 p.p.m. of chlorine 0.1 p.p.m. of chlorine will give an extinction of 0.001, which is the average deviation in the determination of low extinctions with a moderately good photometer. We will assume that a photometric error greater than 0.002 in extinction (about 0.4% in transmittancy) is unlikely a t low extinctions (up to 0.05 or somewhat more). This means that the photometric error will usually be less than 0.002'3$ chlorine when a 0.1-gram sample is used. Table 11.
Stability of Silver Sulfide Sols in Ammoniacal S o htion
(Final Rolution 1.5 M in PiHiOH and 0.001 M in XatS) Concentration Log Io/I (1 Cm.. Blue Filter) of Silver, P.P.M. 10 minutes 1 day 1 week 0.000 0.000 0.000 0
1145 Table 111. Determination of Chlorine in Silicate Rocks by Photometric Sulfide Method Sample Quartz monzonitea
Chlorine Present, % '
Chlorine Found, %
0.019 0.031
0.0196 0.031 0.040 0.062 0.069 0.077 0.100 0.129 0.110 0,022 0.021b 0.042
0.038
DiabaseC
0.069 0.069 0.069 0.100 0.127 0.127 0.020 0,020
0.039 0.070 0.070 0.101 0,101 0.128 0.128 0.188 Chlorine content 0.007%. 0.5-gram samples. NarCO. fusion. b K dithio-oxalate aa photometric reagent. 0 Chlorine content 0.008g. 0.5-gram samples.
0.065
0.065 0.113 0.108 0.133 0.132 0.20 CI added as NaCl before
PROCEDURE
When ample material is available, mix 0.5 gram of 100-mesh sample (0.005 to 0.07% chlorine) with 2.5 grams of sodium rarbonate (low in chlorine) in a platinum crucible and fuse in the 81 customary manner. Digest the cooled melt with about 20 ml. of 108 water, adding a drop or two of alcohol to reduce any manganate present. Filter through a small retentive filter paper (previously washed with water to remove any foreign chloride) and wash with small portions of hot water totaling about 75 ml. Neutralize the The error due to the solubility of silver chloride is largely comcold filtrate and washings by careful addition of 1 to 1 nitric arid, pensated by applying the blank correction obtained by running a using methyl orange as indicator, and add an excess of 0.5 1111. blank on the sodium carbonate under the same conditions as in Add 2 ml. of 0.2 N silver nitrate solution, heat almost to the boiling point, and allow t,he solution to stand overnight. Collect the determination itself. The use of specially purified sodium t,he precipitate in n small glass filter crucible (Jena 1G4) or carbonate very low in chloride is inadvisable in most cases, for it porous porcelain crucible. Wash the beaker, crucihle, and premay be expected to result in less complete cancellation of the cipitate carefully with five 2-ml. portions of 0.02 N nitric acid. solubility error. On the other hand, the chloride content of the Dissolve the precipitate in 2 or 3 ml. of 1 to 1 ammonium hydroxide and wash the crucible with a few milliliters of water. .4 sodium carbonate should be sufficiently low so that the error in hell-jar type of filtration apparatus is preferably used in these the determination of the blank will be small. The following operations. blank values were obtained with various amounts of sodiuni rarTransfer the solution t o a 10-ml. volumetric flask, dilute t o bonate used in the present work: about 8 ml. with water, add 1.0 ml. of 0.01 M (0.25 gram of sodium sulfide nonahydrate in 100 ml.) sodium sujfide solution, mix, dilute to the mark, and again Weight of NaTCOi, g. 0 5 0 5 1.0 1.0 2 5 2 5 5 a 5 mix. Obtain t,he transmittancy of the solution Clfound, y 5 3 13 10 35 30 59 65 53 with the aid of a blue filter (a Wratten No. 47, Equivalent % C1 C5. filter is suitable). in rock samole .~~ ~11, weight- -of Establish t,he s t a i i t l d curve by taking 0, 0.25, KaICOa 0.005 0.003 0.0065 0 . 0 0 5 0.007 0.006 0.006 0.0065 0.00jj 0.50, 0.75, and 1.0 I=g. of silver as silver nitrate in 10-ml. volumvtric flasks, treating witG 2 ml. of 1 t o 1 ammonia and 1 ml. of sodium sulfide solution, and obtaining In these blank runs the volume of the solution in which the t,he transmittancy as described above. Find the amount of chloprec.ipitation of silver chloride was carried out was adjusted to rine from the theoretical ratio Cl/hg = 0.329. correspond to the amount of sodium carbonate, so that the ratio Run a blank by taking 2.5 grams of sodium carbonate a n d was constant. However, proportionately more wash solution was treuting as described above. used for the smaller samples, particularly the 0.5-gram, which is reflected in the smaller apparent chloride content found For the latter weight of sample. Table IV. Determination of Chlorine in Diabase by The advantage in the use of the photometric method over the Photometric Sulfide Method" gravimetric method is especially marked in the case of samples of (0.1-gram samples) 0.1-gram weight. If the error in weighing the silver chloride pre0 008 Cl presentb. (70 0 020 0.022 0.022 0 038 0.040 C1 found, % ' 0.012 0.023 0.019 0.023 0.041 0 046 cipitate may amount to 0.2 mg., the resulting error in the chlorine Similar results obtained with 0.l-grain samples of granitic rooks. percentage is 0.05 compared to about 0.005 in the photometric h Sum of original chlorine (determined o n 0.5-gram sample) a n d added method. chlorine. Biomine is counted with chlorine in the proposed method, but because bromine is almost always very small compared to chlorine in igneous rocks (average bromine-chlorine ratio believed to be of If the amount of sample is limited, fuse 0.1 gram or more with five times its weight of sodium carbonate. Carry out the succeedthe order 0.01), the analytical result may be taken to represent ing operations as described above, but reduce the volumes in prothe chlorine content without appreciable error. The effect of portion to the reduction in the size of sample. Use a small porous phosphate was investigated by adding the equivalent of 1% porcelain or sint,ered-glass filter crucible of about 10-ml. volume phosphorus pentoxide to a sample of granite (0.01% chlorine) and for collect;ng the silver chloride precipitate. Wash carefully with of diabase (0.02% chlorine). The chlorine values found agreed five 1-ml. portions of 0.02 N nitric acid. Dissolve the precipitate in 2 ml. of ammonium hydroxide and proceed as directed. within 0,002'% with those obtained with the omission of phosphate. RECEIVED .4pril 21, 1950. 5.4 10.8 27.0 54
~
~
~
0.024 0.045 0.097 0,188 0.275 0.347
0,022 0.047 0.102 0.187 0.274 0,364
0.021 0.042 0,100 0.192 0.280 0.361
