Quantitative Determination of the Concentration of Vaporized Carbon Tetrachloride JOHN C. OLSEN, Brooklyn Polytechnic Institute, Brooklyn, N. Y. HENRY F. SMYTH, JR., University of Pennsylvania, Philadelphia, Pa. GEORGE E. FERGUSON AND LEOPOLD SCHEFLAN, Pyrene Manufacturing Company, Newark, N. J.
IN
of gas, an electrically driven suction pump was used and the volume measured by means of a gas meter. The various reagents used to absorb the hydrogen chloride are given in the tables.
THE course of investigation of several research problems dealing with low molecular weight alkyl halides of the paraffin series, it became necessary to make a large number of determinations of the concentrations of vapors of these compounds in air. The problem of analyzing such airhalogenated hydrocarbon mixtures is not new and has been dealt with in various ways in numerous chemical and toxicological studies.
Experimental Work SETI. A very satisfactory method was devised to introduce accurately weighed samples of carbon tetrachloride into a stream of air.
Fieldner, Katz, Kinney, and Longfellow (2) found the concentration of vaporized carbon tetrachloride in air by drying the sample over calcium chloride and soda lime, absorbing the organic vapor with weighed activated charcoal, and finding the increase in weight, making suitable deductions for the presence of inorganic halogen compounds. Robbins and Lamson (6) used an apparatus developed by Palmer and Weaver (4)for the determination of carbon tetrachloride in air, in which the resistances of two electrically heated wires, one surrounded by the gaseous unknown and the other by a reference gas, are compared. Nuckolls (3’) found the concentration of carbon tetrachloride, chloroform, dichloroethylene, dichlorodifluoromethane, dichlorotetrafluoroethane, ethyl bromide, ethyl chloride, methyl bromide, methyl chloride, methylene chloride, and monofluorotrichloromethane, respectively, in air by means of a modified Burrell apparatus. “The apparatus consisted essentially of a liquefaction bulb having a side arm connected to a mercury manometer. The inlet of the bulb was provided with a three-way stopcock which connected on one side to a vacuum pump and on the other side to a U-tube, one arm of which was provided with a connection to the sampling tubes.” The water vapor was removed by contact with anhydrous magnesium perchlorate and the sample of halogenated hydrocarbon was frozen with liquid air in the bulb from which the air was then removed by means of a vacuum pump. After returning the bulb to the original temperature, observation of the pressure exerted by the alkyl halide in a mercury manometer and the atmospheric pressure made it possible to calculate the concentration of the halogenated hydrocarbon in the sample.
The tip of an ordinary glass Gooch funnel (Figure 1) was sealed and a narrow arbitrary scale from 1 to 10 was attached along the length of the stem. The funnel was provided with a shellaccovered 2-hole cork stopper through which two right-angular glass tubes had been fitted. The inlet tube was long and drawn to a capillary which reached down to the stem of the Gooch funnel. The outlet tube was short and led to the hot silica tube. Before each run the Gooch funnel was closed with a solid shellac-covered cork stopper and weighed. Then 0.5 ml. of carbon tetrachloride was placed in the stem of the funnel, which was closed with the solid cork stopper and weighed again, thus giving the weight of the carbon tetrachloride used. A wire hook had been fastened around the modified Gooch funnel so that it could be suspended in a balance for weighing purposes. The arbitrary scale had been chosen so that 0.5 ml. of carbon tetrachloride reached approximately up to the 10 mark. Just before starting the run, the solid cork stopper was quickly replaced with the 2-hole stopper mentioned above. A porcelain boat was filled with water and placed in the silica tube, as shown in Figure 1, in order to provide sufficient hydrogen for the formation of hydrogen chloride. In making the run a stream of uncontaminated air was sucked at a definite rate through this carbon tetrachloride vaporizer into the heated silica tube and the reagent bottles. The volatilization of the carbon tetrachloride into the air was kept as constant as possible by slightly raising or lowering the inlet tube within the vaporizer. The internal diameter of the combustion tube was 1.56 em. (0.625 inch). It is important to mount the constricted end of the tube as close to the furnace as possible without burning the rubber tube joint to prevent moisture from condensing in the cold end, which would hold hydrogen chloride in solution. SET11. The experiments in set I1 were conducted in an especially constructed experimental room having a volume of approximately 32 cubic meters. The walls and floor of t.he room were concrete and the ceiling was “transite” asbestos board. The room had five steel casement windows, 70 X 100 cm., four opening t o the outside and one to the adjacent analytical laboratory, and a door in the end of the laboratory wall. The entire inside of the experimental room had been given two coats of sodium silicate, brushed with dilute hydrochloric acid, and finally sprayed with two coats of a Bakelite varnish. Each covering was allowed to dry thoroughly before a new layer was applied to the wall. Two linen towels were suspended in this room and wetted with a measured volume of carbon tetrachloride, taking care that no liquid carbon tetrachloride dropped from the towels onto the floor. Then a powerful fan was turned on in the experimental room for 10 to 15 minutes in order to volatilize the carbon tetrachloride and render the atmosphere in the room as uniform as possible. Afterwards, air was drawn from this experimental room through a glass tube located at the 150-cm. (&foot) level directly into the hot silica tube in the test room and thence into the gas-washing bottles.
Kone of the determinations described seemed suitable to the authors’ purpose, as they were interested in a simple, specific chemical method which could be employed for large as well as small gas samples. Therefore, another method was developed, somewhat similar to that used by Robbins in determinations of carbon tetrachloride in animal tissues ( 5 ) .
Principle of the Method The method is based upon the observation that carbon tetrachloride vapor mixed with moist air is decomposed quantitatively into hydrogen chloride when passed through a silica tube heated to 1000” to l l O O o C. By absorption and determination of the hydrogen chloride the concentration of the carbon tetrachloride vapor can be calculated. If water vapor is not present in sufficient amount, small amounts of chlorine are produced. The accuracy of the method was checked by the determinations of known amounts of carbon tetrachloride vapor. The apparatus used is shown in Figure 1. The silica tube was heated by means of the electrical furnace, the temperature being controlled by means of the rheostat and measured by the thermocouple. The gases were drawn through the train by means of a calibrated water-filled aspirator of 18 liters in capacity. When it was necessary to measure larger volumes
SET111. I n connection with experimental work on the physiological effect of carbon tetrachloride vapor, it was desired to modify the method of determination so that it was suitable for low concentrations, and could thus be used 260
JULY 15, 1936
ANALYTICAL EDITION
26 1
TABLE I. EXPERIMESTAL CONDITIONS AND RESULTS OF TESTS IN SET I
So.
CC14 Used
Mff, 2 3
765.1 765.1 741.5 774.2
4
5
Temp. of Furnace C. 993 1038 1017 1040
Rate L./min. 0.5 0.5 0.5 0.33
(Using known amounts of carbon tetrachloride vapors in air) Volume of CClr Found i n Each Gas-Washing Bottle Sample 1 2 3 4 5 Lzters % % % % % 1.9" 1.7b 0.0 3.8a 10 91.45 10 79.5~ 2 . 3 ~ 1 . 3 ~ 1.3: O.Od 84.0e 4.8e 2.9e 1.5 2.61 9.75 2.81 1.3C 1.51 85.6e 5.4e 8.33
CCla in h r b y Volume Used Found
CCla Found
MQ.
%
%
755.9 645.8 710.4 747.9
98.8 84.4 95.8 96.6
1.20 1.20 1.19 1.45
% 1.19 1.01 1.14 1.40
Reagents used: 50 ml. of 1 N aqueous sodium hydroxide. b 50 ml. of 95 per cent ethyl alcohol. C 50 ml. of 1 N alcoholic sodium hydroxide. d 50 ml. of paraffin oil (used in order t o absorb chlorides or undecomposed carbon tetrachloride, if present). * 50 ml. of 2 N aqueous sodium hydroxide. f 50 ml. of 10 N aqueous sodium hydroxide.
TABLE
S O .
1 2 3 4 a
CC14 Used Grams 50 7 50.7 101 4 101.4
11. EXPERIMENTAL CONDI'PIOXS AND RESULTS O F TESTS IN
SET
11
[Using carbon tetrachloride-air mixtures in experimental room of 32 cu. meters (1130 cu. feet) capacity] Temperatuie Time Volume cc14 Found i n Each Sampling Concentration of CClr of of of Bottlea in Room Furnace Sampling Sample 1 2 3 CClr Found Used Found c. Xin. Lifers % % % % Grams P. p . m. P. p . m. 49 2 97 0 250 243 97 0 0.0 0 0 1100 65 18 72 18 95.6 95 6 48.2 250 239 0.0 0.0 1100 95 0 72 18 93.7 . 0.0 93 7 500 469 0.0 1100 96 4 72 18 95.1 0.0 95.1 500 476 0.0 1100 Av. 95.4
Three gas-washing bottles were used in series, each bottle containing 50 ml. of 10 N aqueous sodium hydroxide. R a t e , 0.5 liter per minute.
as a check on the calibration of more indirect but more rapid methods for estimation. To increase the efficiency of the method slightly, the silica tube was packed with 10-mm. lengths of 5-mm. quartz tubing. The total packed length of the quartz combustion tube was 35 cm. (14inches) with a 30-cm. (12-inch) furnace. Enough of the small packing tubes were used to fill the space, and were held in place with loose plugs of ignited asbestos fiber, about 2.5 cm. (I inch) of plug at each end. After packing the tube, the free flow of air through the tube was tested by gently blowing through one end. It is important to make this simple test, as the asbestos is easily packed too tightly. The chloride absorbed was determined by titration with standard silver nitrate solution (1 ml. = 1 mg. of carbon tetrachloride) using potassium chromate as indicator and working in a darkroom in bright yellow light, as is done in water analyses ( 1 ) . Otherwise, no change was made in the method for these trials. Nine trials were conducted, using air samples of 10 liters as measured by the aspirator bottle (actually close to 9 liters when corrected for pressure drop and water picked up in the aspirator). For lower concentrations of carbon tetrachloride it was desirable to decrease the volume of absorbing fluid to avoid the need for inconveniently large air samples. It was found possible to absorb the hydrogen chloride formed in the silica tube in 50 ml. of 2 N sodium hvdroxide with the same accuracy as in the five absorbing bottlesof the original method, if a fritted glass (Jena) distributing disk was used for the production of fine bubbles, and if 5 ml. of ethyl alcohol ,or 0.5 ml. of 0.1 per cent saponin were added to' reduce bubble size. The determination was carried out as before, save that the sodium hydroxide and washings were made up to only 100 ml. For the measurement of smaller amounts of carbon t,etrachloride (1mg.) with accuracy equivalent to that when weighing 10 mg., a capillary buret similar to that described by Smyth (7)was employed, :L mm. on the capillary corresponding to 0.22 mg. of carbon tetrachloride, and estimates to 0.02 mg. being possible without a reading telescope. In all trials at c o n c e n t r a t i o n s below 100 p. p. m., a buret graduated in 0.02 ml. was used for the titration. As a preliminary to contemplated work on the determination of carbon tetrachloride by automatic means employing a recording conductivity bridge, tests were made of the efficiency of absorption of the hydjfogen chloride formed in distilled water. Fifty milliliters of water in a fritted glass gas wash-
ing bottle were used. The acid absorbed was titrated withsodium hydroxide, 1 ml. of which is equivalent to 1.9235 mg. of carbon tetrachloride. Bromothymol blue was used as the indicator, carrying the titration to a pH of 7. Some error must have been introduced by the carbon dioxide formed in the silica tube, but in view of the results obtained it is judged to be low. Since no formation of free chlorine in the silica tube was desired, tests were made with preliminary humidification of the air before it entered the tube, but after it picked up the carbon tetrachloride. SETIV. The tests outlined in set I1 were repeated using the improved method described in set IV. The changes made included packing the silica tube with a large number of 5-mm. lengths of 5-mm. quartz tubing held in place by loose plugs of ignited asbestos fiber, the use of a gas-washing bottle provided with a fritted glass (Jena) distributing disk 20 mm. in diameter, and the addition of 5 ml. of ethyl alcohol to 50 ml. of 2 N sodium hydroxide.
Titration Procedure
A t the end of the sampling, some additional pure air was drawn through the apparatus in order to flush out any residua1 vapors. As soon as the run was completed the contents of each absorption bottle containing alcoholic or aqueous sodium hydroxide were transferred to a 100- or 200-ml. volumetric
m FYROVOLER
RHEOSTAT
/A----L
FIGURE 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
'262
TABLE 111. EXPERIMENTAL CONDITIONS AND RESULTS OF TESTS IN SET I11 (Using the improved method of determination of known amounts of carbon tetrachloride vapors in air) CClr CClr in by VolTest cc14 No. Used Air ume CClr Found Special Conditions M ~ . ~ g . / i .P. P. m. Mo. % Standard, aave silica tube paoked
48 47 24 29 37 28 30 45 40
19.4 20.7 51.8 56.7 04.7 75.2 140.1 180.2 426.4
2.2 2.4 5.7 0.3 7.2 8.4 15.9 20.2 47.8
350 380 910 1000 1150 1340 2530 3200 7000
Tube packed HCl absorbed in 5'0 ml. of 2 N NaOH saponin
88 91 97 99 98
51.2 55.1 58.5 74.5 98.4
5.0 0.0 0.4 8.2 10.8
950 1020 1300 1720
Tube packed HCl absorbed in {O ml. of 2 N NaOH ethyl alcohol
95 82 81
49.1 64.5 116.3
5.3 7.1 12.8
840 1130 2040
+-
+
Tube packed CClr by volume adsorbed in 9 ml. oftNaOH in spi-
109 110 108 107
1.03 1.80 3.59 11.68
111 112
0.58 3.60
890
0.11 0.20 0.39 1.27
18 32 02 202
0.003 0.39
10 02
ral
Tube packed, absorbed in water: Sample 0% humidity
124 123
52.5 100.0
5.0 10.7
890 1700
Sample 70% humidity
134
43.4
4.0
730
Sample 100% humidi ty
128 130 127 122 120 125 120 121 119 129
32.8 42.4 50.0 52.3 55.4 57.0 04.4 73.3 98.0 138.0
3.0 4.0 5.6 5.7 0.1 0.3 7.1 8.1 10.7 14.8
570 730 890 910 970
1000
1130 1290 1700 2360
19.2 20.0 50.9 55.5 03.3 73.4 137.5 177.8 420.6
99.'0
99.6 98.3 99.6 97.8 97.0 98.1 98.7 98.9 Av. 9 8 . 4 49.9 97.5 54.0 98.0 57.7 98.3 73.8 99.1 95.7 97.3 Av. 9 8 . 0 48.0 97.8 03.5 98.4 114.5 98.4 Av. 9 8 . 2 1.01 9 8 . 0 1 . 8 1 100.6 3 . 0 2 100.8 11.50 9 8 . 5 Av. 9 9 . 6 0 . 5 8 100.0 3.54 98.3 Av. 9 9 . 2 21.0 43.9
40.0 43.8 Av. 4 1 . 9 42.1 99.3 Av. 9 9 . 3
31.8 42.1 50.2 50.5 52.6 50.1 03.9 72.4 97.8 130.4
97.0 99.3 99.2 90.5 95.0 98.4 99.2 98.8 99.8 98. 8 Av. 9 8 . 2
aask and diluted to the mark. Several samples were pipetted out and two different analyses were made. Since all the carbon tetrachloride was to be titrated as sodium chloride, when tests showed some of the chlorine formed during the thermal decomposition was present in the solution in the form of sodium hypochlorite, it became necessary to convert the sodium hypochlorite to sodium chloride. This reduction was brought about by the addition of 0.1 N sodium sulfite. However, in order to ensure the addition of a sufficient amount of this reducing agent, it became necessary to conduct a preliminary analysis for the purpose of determining the sodium hypochlorite concentration of the solution. This is unnecessary when it is certain that the relative humidity of the air sample approaches 100 per cent, since in this case no hypochlorite is formed during absorption. PRELIMINARY ANALYSIS. The test portion was treated with 10 per cent potassium iodide and acidified with dilute hydrochloric acid. The iodine liberated by the interaction between the potassium iodide and the sodium hypochlorite was titrated against 0.1 N sodium thiosulfate, using starch as indicator.
VOL. 8, NO. 4
PRINCIPAL ANALYSIS. As the volume of 0.1 N sodium thiosulfate used in the preliminary analysis was a direct measure of the sodium hypochlorite concentration of the solution, this volume was taken as an indication of the proper amount of 0.1 N sodium sulfite to be added t o the sample. Actually, the amount of 0.1 N sodium sulfite added exceeded the volume of 0.1 N sodium thiosulfate used by 10 per cent. The solutions taken for analysis were treated with the proper amount of 0.1 N sodium sulfite and a few drops of phenolphthalein; enough dilute nitric acid was added to make the solution only faintly alkaline to phenolphthalein. The samples were allowed t o cool to room temperature, 2 ml. of 1 M sodium bicarbonate were added, and the solutions were made just faintly alkaline to litmus with dilute nitric acid. Then 2 drops of 10 per cent potassium chromate were added as indicator and the solutions were titrated with standard silver nitrate, using yellow artificial light and excluding daylight. In the case of the nonalkaline reagents some aqueous sodium hydroxide was added at the end of the run and the analysis was conducted as given above. Suitable blanks were run in every case and proper deductions were made to account for chlorides present in the reagents and the atmosphere.
Experimental Results and Conclusions Tables I to IV give the conditions and data in the four sets of experiments described above, and clearly indicate that this method is well adapted for the determination of the concentration of vaporized carbon tetrachloride in air. I n carrying out the determination given in Table I, various absorbing reagents for the hydrogen chloride were tried. As even the fifth bottle showed appreciable amounts of chloride, it is obvious that absorption was not complete with the type of absorption vessel and procedure used. The results given in Table I11 showed an average of 98.6 per cent of the carbon tetrachloride accounted for, with concentrations from 350 to 7600 parts per million by volume. Varying the sampling rate from 250 to 1000 ml. per minute did not affect the accuracy of the method. Five trials a t concentrations between 890 and 1720 p. p. m. with saponin averaged 99.1 per cent recovery and three with alcohol 98.2 per cent recovery, as indicated in Table 111. When using the capillary buret, previously described, samples of 10 liters of air with carbon tetrachloride concentrations ranging from 18to 202 p, p. m. gave recoveries averaging 99.5 per cent when saponin was used in 50 ml. of sodium hydroxide. Similar trials where the hydrogen chloride formed was absorbed by 9 cc. of sodium hydroxide in a spiral absorber similar to that described by Smyth (7) gave recoveries averaging 99.1 per cent for concentrations of 10 to 62 p. p. m. It is believed that 10 p. p. m. is not the lower limit of accuracy of the method, although no present need required trials with lower concentrations. Using water as absorbent, it was shown that 70 per cent humidity (obtained by bubbling the air sample through 10 N sodium hydroxide) prevented the formation of chlorine, and data reported in Table 111 show that a t this humidity determination of hydrogen chloride by absorption in water is accurate. Ten trials with 100 per cent humidity (obtained by bubbling the air sample through water) showed recoveries averaging 98.2 per cent with concentrations between 570 and 2360 p. p. m., just as good as when the hydrogen chloride was absorbed in sodium hydroxide.
TABLEIV. EXPERIMENTAL CONDITIONS AND RESULTS OF TESTSIN SETI V (Using carbon t,etrachloride-air mixtures in experimental room of 1130 oubic feet capacity and utilizing the improved method of determination) Temperature Time Volume cc14 Found in Conoentration of CCI4 of of of Each Sampling Bottle" CCL in Room No. Used Furnace Sampling Sample 1 2 Used Found Grams c. Min. Liters % % % Grams P. P. m. P. P. m. 1 2 3 4
101.4 101.4 101.4 50.7
1100 1100 1100 1100
72
72
72 72
18 18 18 18
97.2 97.7 96.5 97.0
0.0 0.0 0.0
0.0
97.2 97.7 96.6
97.0
98.0 99.1 97.8 49.2
600 500 500 250
480 489 483 243
Av. 9 7 . 1 The first absorption bottle contained a fritted disk, while the second waa of the ordinary type. t
1
JULY 15, 1936
ANALYTICAL EDITION
The experiments outlined in Table IV again indicate the quality of the results obtained with the improved method in the experimental room. However, experiments carried out in such a test room can yield good results only if (1) the atmosphere ii3 uniformly mixed, (2) the test room is sufficiently tight so that there will be no appreciable flow of atmosphere from the test room to the outside, or vice versa, during the course of the test, and (3) the surface of the interior of the test room does not react with any constituent of the atmosphere tto be tested. The experiments can become highly unsatisfactory if any of these conditions is not fully satisfied. The thermal decomposition method with the slight modifications given accounts for a t least 97.3 per cent of carbon tetrachloride vapor present in air, down to a concentration of 10 p. p. m., and probably lower. Since absorption in distilled water will give recoveries of almost this degree, the method is suitable for development of continuous automatic indicating equipment based on electrical conductivity. It is believed that the chemical method described, as well as the
263
electrical method suggested, is generally applicable to the quantitative determination of vaporized halogenated hydrocarbons other than carbon tetrachloride in air. It is planned to conduct further tests in this field in order to confirm this conclusion.
Literature Cited (1) Am. Pub. Health Assoc., “Standard Methods for the Examination of Water and Sewage,” 7th ed., New York, 1933. (2) Fieldner, A. C., Katz, S. H., Kinney, S. P., and Longfellow, E. S., J . Franklin Inst., 190, 543 (1920). (3) Nuckolls, A. H., Underwriters’ Laboratories’ Report, Miscellaneous Hazard No. 2375 (November 13, 1933). (4) Palmer, P. E., and Weaver, E. R., BUT.Standards Tech. Papers 249 (1924). (5) Robbins, B. H., J. Pharmacol., 37, 212 (1931). (6) Robbins, B. H., and Lamson, P. D., J. Pharmacol., Proc., 31, 220 (1927). (7) Smyth, H. F., Jr., J.I d . Hug., 9, 338 (1929). RECEIVED March 31. 1936
Determining the Resistance of Portland Cement to Sulfate Waters An Accelerated Test R. W. STENZEL, Metropolitan Water District of Southern California, Banning, Calif.
D
U R I N G t h e p a s t few years many investigations
is e c o n o m i c a l l y feasible. A number of specifications have recently been written with a restriction of this nature, notably those of t h e M e t r o p o l i t a n Water District of Southern California @), and of the Bureau of R e c l a m a t i o n (S), and the r e s u l t s of t e s t s have shown that this procedure has been r e a s o n a b 1y we 11 justified. Nevertheless, it is not to be presumed that a similar sulfateresis tance-compound-composition r e l a t i o n s h i p will necessarily hold for other geographical areas where the raw materials and m a n u f a c t u r i n g practice mav be somewhat different. Therefore it is desirable to have a reliable short-time test which will directly measure the sulfate-resistance of a cement and whose results will be available by the time the usual 28-day strength tests are completed. One such test has been incorporated in the specifications (7) for the Fort Peck Dam, Montana, but no data regarding the results of its use and comparison with actual concrete tests have been published. The slab-warping test which is here described has been applied to Portland cements having a wide variation in chemical composition, and has been found to give a good correlation with long-time compressive strengths of the corresponding mortar and concrete cylinders. Since it is fundamentally an expansion test, it must be used with caution on cements other than the Portland variety, such as cements with pozzuolanic admixtures, and it is not applicable to highalumina cements in which sulfate disintegration may proceed without external volume changes. The test consists in casting a neat-cement specimen 5 x
The present active interest in the manufacture of Portland cements which will produce concretes highly resistant to the action of natural waters has created a need for a reliable but short-time laboratory test to determine this resistance. The slab-warping test herein proposed is believed to give a reliable indication of the probable resistance of the cement to sulfate-bearing waters, and compares favorably with longtime tests of concrete cylinders made from the same cement. It has the merit of being completed within 28 days, so that it is suitable for acceptance test purposes.
have been made On the resistance of Portland cement concrete to corrosive salt waters. The conclusions regarding the actively c o r r o s i v e constituent therein have almost been that the sulfate ion is primarily responsible for the reactioru leading to the eventual disintegration of the conCrete. I t is likewise now generagreed that even the most dense p r a c t i c a1 combinations of aggregates and cement will not resist the corrosive action ofhighly sulfated natural waters. It is only by the use of a cement which does not readily react with sulfates that long life of an exposed concrete structure is to be expected. The preponderance of experimental evidence indicates that, if the cement is made under conditions obtaining in the best modern practice of manufacture, its resistance to sulfate action can be reasonably well deduced from its chemical composition. The method is to compute the hypothetical compound composition from the results of the usual chemical analysk;, as proposed by Bogue ( I ) , and then from the percentage of the sulfate-sensitive compounds to estimate its probable resistance. The tricalcium aluminate is widely regarded as the source of all evil in the family of cement compounds in most of those properties which tend to make concrete less durable, and indeed its properties-i. e., those of the pure compound-fully warrant these suspicions. Therefore the present practice in consumer specifications, when a high Bulfate-resistance is desired, is to specify a composition which will make the percentage of this compound as low as
