628
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Vol. 13, No. 7
The Calcium Chloride Method for the Determination of Water in Gasoline and in Certain Other Substances‘ By Charles W. Clifford CHEMICAL LABORATORIES, DEVELOPMENT DEPARTMENT, THE GOODYEAR TIREA W
During an investigation in this laboratory it became desirable to obtain and verify, or to construct, the solubility curves for water in a certain gasoline and in benzene. This information is essential in many cases where a comparatively large change in temperature would cause separation of water from these solvents. The only useful reference in the literature is to the work of E. Groschuff,* who determined solubilities of water in paraffin oil, kerosene, and benzene by heating and cooling definite amounts of the liquids with water in sealed tubes and noting the temperatures a t which turbidity disappeared and reappeared. The original article was not available, but the two abstracts apparently covered all the essential points.
RUBBERCO., AKRON, OHIO
The most promising method, then, were: 1-The sodium method of Graefe. 2-Volatilization of the sample and absorption of the moisture in a dehydrating agent which would not absorb or react with the oil vapor.
Three 2.5-liter samples of this gasoline were secured a t different times. The specific gravity was taken on the fresh sample with a pycnometer. All samples were kept securely stoppered in glass-stoppered bottles to avoid loss of the lighter fractions, and specific gravity determinations made on these samples from time to time gave constant values. This gasoline had R gravity of 0.70 (70” Be.), and it was a “straight run” product. The initial boiling point was 40” C., and the “dry point’’ 145” C. INVESTIGATION OF POSSIBLE METHODSFOR DETERMINATION THESODIUMMETHOD OF WATERIN GASOLINE A constant-temperature bath was set up to maintain With the procedure described above, the solubility is temperatures from 5” to 50’ C., so that samples might be somewhat affected by change in pressure, and, therefore, saturated with water a t the desired temperatures. I n testing the higher the temperature, the greater the pressure in the the apparatus described by Allen and Jacobs1 for the determisealed tubes, and the more deviation from the true value nation of water by treatment with sodium, it was found that a t atmospheric pressure. Whether the solubility under 100 cc. of saturated gasoline would yield only 4 or 5 cc. of pressure a t a given temperature will be increased or decreased hydrogen, and that considerable time elapsed before the depends upon whether solution is accompanied by contraction evolution was complete. Also, it was practically impossible or expansion in volume. The effect of the small pressure to avoid some leakage during this time. in these cases of very slight solubility was perhaps negligible, A simple one-piece apparatus was devised so that absolutely but with a gasoline having an initial boiling point around no leakage could occur, but here a vapor pressure correction 40” C. the pressure might become an important factor. The became necessary. Attempts were made to determine the application of this method would also present practical vapor pressure of this gasoline by the “barometer method,”2 difficulties in sealing the tube, when applied to gasoline. and results of from 168 mm. to 704 mm. Hg were obtained. Therefore it seemed desirable to determine solubilities of Since gasoline is not a single chemical compound, but a mixwater in gasoline by some other method, and to compare ture, its vapor pressure will vary with the boiling points the resulting values with those given for kerosene and paraffin of its constituents, the temperature, and the ratio of volume oil. of sample to the space into which it can vaporize. Tubes Allen and Jacobs3 enumerate ten methods for the determi- of various heights filled with this gasoline alone also gave nation of water in petroleum products. Only one of these varying results. Calculation of the vapor pressure values3 (the method of Graefe 4 which consists of treatment with was not attempted. A table4 of gasoline vapor pressure sodium and measurement of the evolved hydrogen) seemed values is given in the literature, but the method of deteraccurate enough for this problem where such a small amount mination is not specified, and, since the boiling point of the gasoline quoted is considerably higher than that of this of water can be dissolved. A study of other possibilities suggested a number of meth- gasoline, the values for this gasoline could not be safely ods, including the following: (1) by calculation, based estimated. on the difference in specific gravities of the sample before The sodium method, therefore, was considered unsatisand after dehydration; (2) by freezing out the water by factory for the determination of these small amounts of immersion in a low-temperature bath; (3) by dilution with water in gasoline. an oil dissolving much less water than gasoline; and (4) THECALCIUMCHLORIDE METHOD by selective absorption of water from the vaporized sample In the literature no mention is made of the ordinary by some suitable reagent. Method 1 has been shown by Graefe to be inaccurate for drying agents, phosphoric anhydride, sulfuric acid, and anwater in crude petroleum, and in the case of dissolved water hydrous calcium chloride, although the use of plaster of in gasoline the difference in specific gravities would probably Paris (both qualitatively6 and quantitativelye) is given. be less than one in the fourth decimal place. Method 2 It seemed reasonable to expect that calcium chloride, a is not a very practical one. Method 3 is difficult, since practically neutral salt, might prove a satisfactory selective gasoline dissolves an extremely small amount of water, and absorbent, while phosphoric anhydride and sulfuric acid is itself often used to precipitate water “quantitatively” might react with substances in the gasoline. from other organic liquids. Method 4 seemed worthy of 1 L O C . ctt. 2 Holde-Mueller, “Examination of Hydrocarbon Oils,” 1916, 45. trial, although no mention is made in the literature in regard 3 Williamson, “Pressure and Temperature Relations for Vapor of to employing the most common dehydrators. Received September 23, 1920. 2 Elektrochem., 17 (1911), 348; C.A , , 6 (1911), 2550, J . Chem. Soc Abs., 100, 11, 595. Bureau of Mines, Technical Paper 26 (1912). 4 Petroleum, 1 (1906), 813; J . Soc. Chem. I n d . , 26 (1906), 1035. 1
,
Liquids,” Chem. Met. Eng., 22 (1920), 1151. Olsen, Van Nostrand’s “Chemical Annudl,” 1918, 541. 6 Allen, “Commercial Organic Analysis,” 1916, 111, 116; cf. Lunge, “Coat Tar and Ammonia,” 1909, I, 320. 6 Gill, “ 0 1 1 Analysis,” 1918, 22; cf Allen, “Commercial Organic Analysis,” 1916, I. 430.
July, 1921
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
QUALITATIVE TESTS-A very delicate test for water in gasoline was desired, in order that the portion of sample remaining after each trial run might be tested and the presence or absence,of water ascertained. A comparison of three qualitative tests was made, with the results shown in Table I.
TABLE I-COMPARISONOF QUALITATIVE TESTS FOR WATERIN GASOLINE Reagent Sodium KMn.04 AlClr (Anhyd.) Indication of water. Evolution of HZ Solution Evolution of HCI Gasoline dehydrated with N a Negative Negative Negative Gasoline, partly saturated. Positive Negative Negative Gasoline, saturated, Positive Negative Negative
.................. ........ .. ........
The qualitative test with sodium, therefore, is the only satisfactory one of the three enumerated.
Air- +
629
for 2 hrs., the bulb was removed, and dry air alone passed for 2 hrs. The results of this test appear in Table 111. TABLE 111-TEST
QUANTITATIVE RECOVERY OF WATER ADDEDTO ANHYDROUS GASOLINE No. of absorption tube. 1 2 3 Increase in weight, mg . . . . . . . . . . . . . . 62.2 1.0 0.6 Actual water added, rng.. 61 .O Water recovered, allowing blank of 0 . 6 mg 62.0 OF
.............
............... .................
...
...
The remaining portion of the gasoline sample was tested with metallic sodium, and water was found to be entirely absent. These results show that the water added was entirely recovered, and indicate that the method is accurate for water in gasoline. Solubility determinations with additional blanks (described in a following paper’) and later results furnish additional proof of the accuracy of this method. These results show that the water is entirely recovered in the first two absorption tubes, and that the first of these absorbs all except about 1 mg. The correct method of calculating results is found to be:
+
-
(Increase, Tube 1 Increase, Tube 2) 2 (Blank) (Volume of sample) X Specific gravity per cent water by weight FIQ. 1 PRELIMINARY TESTS-TeStS were carried out in the apparatus shown in Fig. 1. Samples of water-saturated gasoline were volatilized with dry air, and the water was absorbed in the reagent contained in the U-tubes. The rate of air flow employed was 5 to 15 liters per hr. Separate tests were made with phosphoric anhydride, sulfuric acid, and calcium chloride; in each case the drying tower contained the same dehydrating agent as the absorption tubes.1 The first U-tube after the drying tower merely protected the sample from foreign moisture. The absorption tubes filled with phosphoric anhydride, and especially those containing sulfuric acid, increased in weight out of all proportion to the dissolved water. The first tube containing calcium chloride showed a reasonable gain of a few milligrams, and the remaining gasoline from this trial run gave a negative test for water with metallic sodium. Further tests were made, therefore, with calcium chloride. This reagent was ‘IC. P. anhydrous” in small lumps, produced by a reputable firm; it was crushed and screened rapidly, rejecting all except the portion from 10- to 20-mesh. BLANK DETERMINATION O N GASOLINE-A sample of the gasoline was dehydrated with metallic sodium. About 39 g. of this anhydrous material were placed in a Vanier bulb, which was substituted for the larger gas-washing bottle employed in the previous tests. Air was passed through for about 2 hrs., then the Vanier bulb was removed, and dry air alone passed for over an hour. Table I1 summarizes the results obtained.
TABLE11-BLANK DETERMINATION ON GASOLINEDEHYDRATED WITH
METALLIC SODIUM No. of absorption tubel. ............... 1 2 3 Increase in weight, m g . . 0.9 0.7 0.9 The tubes are numbered in the order shown in the sketch from left to right, excluding the tube which made certain that n o moisture from the air passed through to the sample and following tubes, No data for this tube are given in these tables. It was weighed with the other three tubes, I t s gain in weight was in most cases about 1 mg. or less.
...............
The results show that the blank is small and fairly constant. TEST FOR QUANTITATIVE RECOVERY O F ADDED WATER-
The Vanier bulb containing anhydrous gasoline was next weighed, and reweighed after the addition of three drops of water from a 1-cc. pipet. The bulb was connected, and air was passed through. When the contents were shaken so as to suspend the water in fine droplets and allow good circulation, this water was apparently carried over in 0 . 5 hr. Without shaking, more time would have been required. Air was passed 1
Fresenius-Cohn, “Quantitative Analysis,” 1911, 11, 51.
The dissolved or suspended water in any petroleum product can probably be determined satisfactorily by this calcium chloride method, first diluting the substance, if necessary, with anhydrous gasoline or kerosene. APPLICATION OF THE CALCIUM CHLORIDE METHOD TO BEN-
accuracy of this method as applied to water in benzene was next investigated. This material was of the grade known as “100 per cent benzol,” and when dehydrated had a specific gravity of 0.856 in air. The “dry point” was 80” to 82” C., and the liquid was clear and colorless. Blanks were run on both Na- andCaCl2-dehydrated material. The average blank (from a total of 26 values) was 0.3 mg. Three tests for quantitative recovery of added water were made, and the results were as follows: 57.8 mg. taken, 56.9 mg. found; 44.0 mg. taken, 4 5 . 1 mg. found; 101.2 mg. taken, 101.8 mg. found. The remaining benzene from one run was again analyzed for water, and blank values were the result. The benzene remaining after each run was tested with metallic sodium, and water was entirely absent in each case. These results show that water in benzene can be accurately determined by this method. EXTENSION OF METHOD TO WATERI N OTHER SUBSTANCES The possible application of this method to other organic solvents and many solid substances offered an interesting field for investigation. If applicable, the method would furnish a ready means for determining large and small percentages of water and would preclude danger of decomposition, oxidation, or loss by vaporization which might occur upon heating. Its accuracy was tested with some other liquids, using a Vanier bulb as a container in most cases. The method was also applied to a number of solid substances, using a gas-washing bottle as a container. Where convenient, tests were made with (a) samples of the solid alone, (6) samples suspended in a suitable tested medium (imm‘scible with water), and (c) samples dissolved in a suitable tested solvent (immiscible with water). CHLOROFORM-The chloroform was of U.8. P. grade. After dehydration with CaC12, the specific gravity was 1.481 in air. The average blank was 1 . 2 mg. (average of eight values, including three from one run on a CaClz-dehydrated sample). With an anhydrous sample to which 38.0 mg. water had been added, 36.6 mg. were found upon analysis, and the water disappeared from the suspension in 0 . 5 hr. These results indicate that the method is accurate for water in chloroform. ZENE-The
1 THISJOURNAL, 13
(1921), 631.
630
T H E J O U R N A L OF I N D U S T R I A L AAND ENGINEERING C H E M I S T R Y
CARBON TETRACHLORIDE-The sample was obtained by allowing the technical product to stand over sodium hydroxide, and then distilling over calcium chloride. It was clear, colorless, and neutral, and its specific gravity in air was about 1.60. The blank on this material was 0 . 6 mg. (average of six values, including those from one run on a CaClZ-dehydrated sample). After 47.2 mg. of water had been added to an anhydrous sample, 48.2 mg. were found upon analysis. This method, then, is accurate for water in carbon tetrachloride. CARBON BISULFIDE-This was obtained from technical material by one distillation over calcium chloride. It was clear and colorless, and had a specific gravity of 1.25 in air. The blank was 0 mg. (average of seventeen values, including those obtained with one test on a CaClz-dehydrated sample). 59.3 mg. of water were added to an anhydrous sample and upon analysis60.3mg. were found. The method is apparently satisfactory for water in carbon bisulfide. ETHER-one test was made on U. 8.P. ether saturated with water. The results indicated that the method is probably applicable to water in ether. ACETONE-Technical acetone was distilled over calcium chloride, A portion of the distillate was shaken with fresh calcium chloride and allowed to stand several days, after which it was decanted, again shaken with calcium chloride, and allowed to stand. I n these treatments the calcium chloride swelled to several times its original volume. When a sample of the clear supernatant acetone from the second dehydration was taken and an attempt made to obtain a blank by the calcium chloride method, the results showed that large amounts of acetone were held by the calcium chloride and that determination of water in acetone by this method is impossible. PYRIDINE--SVhen an attempt was made to dehydrate pyridine with calcium chloride, the latter swelled enormously. This was considered sufficient indication that pyridine would react with or be absorbed by the calcium chloride in the absorption tubes, and that the method was inapplicable. ETHYL ALCOHOL-Atest indicated that water cannot be removed quantitatively from ethyl alcohol by means of a current of dry air, as with gasoline. This test also indicated that the alcohol vapor is held to a certain extent by the calcium chloride in the absorption tubes, and that only after prolonged passage of dry air is the vapor displaced to a definite point. The calcium chloride method is therefore probably not applicable to water contained in alcohol. GLYCERoL-One test run made with glycerol indicated that, as with alcohol, the water cannot be entirely removed in several hours by a current of dry air. This run, however, gave a small and constant blank. (Glycerol does not vaporize to an appreciable extent under these conditions.) The calcium chloride method is probably not applicable to the determination of water contained in glycerol. CASTOR om-Castor oil was taken as a fairly typical oil of vegetable origin. One run with the oil dissolved in anhydrous benzene indicated that water in castor oil could probably be determined by this method. SUCROSE-TWO samples (one air-dry and the other moist) of granulated refined cane sugar were analyzed for water by the CaClz method, using 10- to 15-g. portions. The actual moisture in each sample was determined by heating about 10 g. to constant weight (1.5 hrs.) in a ventilated electric oven a t 105' C., and the duplicate values obtained agreed within 0.002 per cent with each sample. The only run made with the air-dry material checked within 0.001 per cent of the average value obtained by heating. Of three runs on the moist sucrose containing about 0.3 per cent water (with the sample alone, suspended in anhydrous
Vol. 13, No. 7
benzene, and suspended in anhydrous carbon tetrachloride), the first result was within 0.002 per cent of the average value obtained by heating, the second was within 0.005 per cent, and the third checked this average value. With the sucrose taken alone, indications were that 0 . 5 hr. was sufficient to carry over all water. These results probably justify the conclusion that moisture in granulated sucrose can be accurately determined by the calcium chloride method. ZINC OXIDE-The technical material intended for use as a pigment was employed. Results on two samples (taken alone, and suspended in anhydrous benzene) were much below the moisture values obtained by heating in the 105' C. oven to constant weight. The calcium chloride method, therefore, is not applicable. CALCIUM CARBON-4TE-ThiS was technical material intended for use as a pigment. Two samples were analyzed for moisture, one alone and the other suspended in anhydrous carbon tetrachloride. The results in both cases were only a fraction of the value obtained by heating a t 105' C. to constant weight. The calcium chloride method is evidently not accurate for moisture in this pigment. . RUBBER sTocK-Small, freshly cut pieces of an uncured, reclaimed stock were weighed out. These pieces swelled but did not disintegrate when benzene, carbon bisulfide, carbon tetrachloride, or a mixture of these was added and a current of dry air passed through. The results obtained in these runs were very much lower than the value accepted as correct (obtained by heating samples for 2 hrs. a t 105" C. in a very efficient vacuum dryer), and the calcium chloride method was considered inapplicable under these conditions.' SULFUR-A test to determine moisture in flowers of sulfur was made, employing anhydrous carbon bisulfide as a solvent. The loss (0.034 per cent) after heating 4 hrs. a t 70" C. was considered as representing the actual moisture present. The blank was small, but the results of this run showed no absorption of water. The calcium chloride method, therefore, cannot be considered applicable. OXALIC ACID AND COPPER SULFATE-TeStS on these substances in crystalline form would give some information as to whether water of crystallimtion can be determined by the calcium chloride method. Using materials of C. P. grade, the water was completely removed from the oxalic acid, while copper sulfate lost none. It seems from these results that air dried over calcium chloride may or may not remove water of crystallization in the time specified, depending upon the vapor pressure of the substance. DESCRIPTION OF METHOD This method, then, is essentially as follows: A current of air previously dried by calcium chloride is passed through, or brought into intimate contact with, the sample a t the rate of 5 to 15 liters per hr. for from 1 to 2 hrs. If a part of the water has settled out in the sample, it must be kept in SUSpension by frequent shaking, or by the current of air itself in order to secure complete vaporization in the time specified. The moisture abstracted from the sample by this air is absorbed in two calcium chloride tubes. If the sample is an appreciably volatile substance or is suspended or dissolved in such a substance, as gasoline, passage of a current of dry air direct from the calcium chloride tower a t the rate of a t least 5 liters per hour for a t least 1 hr. is necessary in order to displace the vapor from the tubes before weighing. When the sample has an inappreciable vapor pressure and is taken alone, as sucrose, the tubes may be weighed immediately after absorption. A third CaClz tube is advisable in order to secure a blank value for correction of results. Before each weighing, the tubes should be wiped carefully and all The application of this method to molsture in pure unvulcanized gum (which can be readily dispersed in benzene or other solvents) was not investigated.
July, 1921
THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY
631
SUMMARY
lowed to reach the temperature of the balance. Suitable precautions should be taken to minimize introduction of air containing moisture, and the action of certain vapors o n rubber connections. If, a t the close of any run, there is doubt in regard to quantitative dehydration of the sample, the remaining portion may be analyzed again by this method, or a suitable qualitative test for water applied. The calculation of results is simple, and (for liquid samples) has been described above. In all of these tests, where weighed amounts of water were added to liquids immiscible with water, the results show quantitative recovery within the limits of experimental error1 (about 1 mg.). I n tests where water was added to, and thoroughly suspended in, the liquid sample, it was noted that all water was apparently carried over in less than 0 . 5 hr. The explanation of results obtained with all the liquids described lies in the law of partial pressures: I n the cases where water was taken with an immiscible liquid, the vapor pressure of the water was the same as though the water existed alone, while in the cases where water was miscible in all proportions with the liquid, the water vapor pressure was markedly lowered and slow vaporization resulted. The small amount of alcohol in the chloroform used apparently did not affect the blank or the quantitative test. I n the case of ether, which dissolves a comparatively large amount of water (the sample contained some alcohol also), the indications were nevertheless that this method could be successfully applied. Obviously, any suitable dehydrator might be substituted for calcium chloride in cases where the vapor of the sample would not react with, or be held by, the dehydrator, and the method is applicable to moisture in gases when such a dehydrator is used,
1- The sodium method is inapplicable to the determination of the small amounts of dissolved water in gasoline. 2-The calcium chloride method herein developed is accurate for the determination of water in gasoline, benzene, chloroform, carbon tetrachloride, and carbon bisulfide. Whether the water in these liquids is in solution or in suspension makes no difference in the accuracy of the method. The method should be accurate for water in any liquid with which it is entirely immiscible. It is probably accurate when applied to water in ether and in suitably diluted vegetable oils. 3- Acetone, pyridine, ethyl alcohol, and glycerol cannot be analyzed for water by the calcium chloride method. The first three, liquids which are miscible with water and appreciably volatile, are held to some extent by the calcium chloride and cannot be readily displaced. Ethyl alcohol and glycerol do not give up all contained water readily when dry air is passed through. The prediction may be safely made that this method will not be satisfactory for water contained in any liquid with which it is completely miscible. 4-The calcium chloride method is apparently accurate for moisture in granulated refined sugar (with the sample taken alone, or suspended in anhydrous benzene or carbon tetrachloride). 5-The method was unsuccessful when applied to moisture in the pigments examined (zinc oxide and calcium carbonate), in flowers of sulfur, and in a rubber stock. B--Water of crystallization may or may not be accurately determined by this method, depending upon the vapor pressure of the compound.
~~~
The Solubility of Water in Gasoline and in Certain Other Organic Liquids, Determined by the Calcium Chloride Method By Charles W. Clifford THE GOODYEAR TIRE CHEMICALLABORATORIES, DEVELOPMENT DEPARTMENT ,
The actual solubility of water in the gasoline and in the benzene previously described3 was sought, in order to determine the importance of this factor in a case where water appeared in cements containing these solvents. The calcium chloride method was employed for this determination. SOLUBILITY OF WATERI N GASOLINE The apparatus described in the preliminary tests of the method was used, and the air was passed successively through a gas-washing bottle, through a U-tube containing calcium chloride, through a gas-washing bottle containing the sample, and through three U-tubes filled with calcium chloride. After passing air from the compressed air line a t the rate of 5 to 15 liters per hr. for about 1 hr., or until the U-tubes had attained constant weight, a 100-cc. sample of the saturated gasoline was carefully introduced and air again passed for 2 hrs., or until about one-fourth of the sample had been volatilized. The bottle containing the sample was then cut out and dry air passed for 1 hr. The tubes were then wiped thoroughly, allowed to reach the temperature of the balance, and weighed. Care was taken in manipulation that no air containing moisture was admitted into any piece of the apparatus, and where rubber connections were necessary as little surface as possible was exposed. The air from the last calcium chloride tube passed through a long glass 1 T h e experimental work was limited by the amount of time available, but each test was very carefully performed. Received September 23, 1920. See preceding paper.
I
AND
RUBBERCo.,
&IRON,
OHIO
tube which dipped under water, thus permitting the rate of air flow to be gaged approximately. Qualitative tests with metallic sodium on the rema.ining portions of several TABLEI-SOLUBILITY OF WATERIN GASOLINE: SUMXARY OF RESULTS B Y THE CALCIUM CHLORIDE METHOD Grams Saturation' Water Conditions Increase in Weight per 100 Temp. hTumber Fraction2 Mi:!igrams Grams C. Hours of Run of Sample Tube' 1 Tube 2 Tube 3 Solution 37.5 3.5 1 a 11.5 3.3 0.0175 1.7 2.4 37.5 3.5 1 b 2.6 2.5 37.5 3.5 1 C 37.5 3.5 1 d -1.1 0.2 ...... 37.5 3.6 2 a 10.7 2.0 0.0145 1.8 3.2 37.5 3.5 2 b 37.5 3.5 2 C 2.6 2.1 37.5 3.5 2 d -1.0 6.0 ...... 35.0 5 3 a 11.2 2.6 1.7 0.0161 35.0 5 4 a 10.0 1.0 0.0121 25.0 3 5 a 6.4 2.1 0.0085 25.0 3 5 b 0.0 1.0 ...... 25.0 3 6 a 7.1 3.1 0.0110 25.0 3 6 b 0.0 0.0
...
... ... ... ... ... ... ... ... ... ... ... .,. ... ... ... ... .. ,. .. .+. ...
...... ...... ...... ......
...... ...... ......
Dehydrated (Blank) 7 1.4 1.7 Dehydrated (Blank) 7 1.0 1.7 Dehydrated (Blank) 8 2.2 1.1 Dehydrated (Blank) 8 1.3 1.1 Dehydrated (Blank) 9 0.6 0.4 Dehydrated (Blank) 9 0.2 0.0 Dehydrated (Blank) 10 1.0 0.7 Dehydrated (Blank) 10 0.3 2.0 1 It was noted t h a t after thorough agitation, the time necessary for complete settling out of water from this gasoline varied from 0.7 hr. a t 27 ._ S o to more than ~. 10 ~ hrs ~s-. t ~ Iso.. . .-. ._ 2 These letters designate successive fractions of the 100-cc. sample volatilized by passing air for 2 hrs. (A test showed t h a t for volatilizing successive fouvths of the sample passage of air for approximately 2, 4, 7, and 20 hrs., respectively, were required.) 3 The tubes are numbered in order, starting with t h a t nearest the sample and excluding the tube which made certain t h a t no moisture in the air passed through the drying tower to the sample and following tubes.
__
~
~
...... ...... ...... ...... ...... ......
