ANALYTICAL CHEMISTRY
348 Table I.
Determination of Total Iron (FenOa) in Soil
(With ceric and Versenate titrations after perchloric acid digestion and after sodium carbonate fusion) % FezOt, HClOl Digestion % FezOa, NazCOt Fusion Ceric Versenate DifferCeric Venenate DifferSoil titration titration ence titration titration ence Oquawka 1.51 1.49 +0.02 1.57 1.55 +0.02 Toledo 2.06 -0.01 2.07 2.07 2.04 iO.03 Oblong 2.25 -0.03 2.29 2.28 2.31 -0.02 Aledo 3.49 3.44 +0.05 3.45 3.49 -0.04 Kewanee 3.41 3.33 +0.08 3.36 3.38 -0.02
-
~
Table 11.
~~
cobalt in soil (S), as well as for the decomposition of silicates for the determination of total iron (Tables I and 11). The residue. after digestion with perchlorio acid and filtration, was treated with hydrofluoric acid; no measurable amount of iron was found. .4s indicated by Holmes (S), there may be soils high in certain unweathered minerals which are not sufficiently decomposed k)y perchloric acid digestion. I n such cases, the insoluble residue may be decomposed by repeated treatments with hydrofluoric acid, evaporated to dryness, taken up with 1 N hydrochloric acid and added to the filtrate.
Determination of Total Iron in Standard Samples by Versenate FelOa Present,
Fez08 Determined,
% Sample" Flint clay 97 0.98 Plastic clay 98 2.05 From Xational Bureau of Standards.
Difference,
%
70
0.97 2.00
-0.01 -0.05
ACKNOWLEDGMENT
The authors wish to thank G. F. Smith of the Chemistry Ilcpartment for his helpful suggestions and discussions, LITERATURE CITED
were obtained by adding an excess of Vcrsenate and back-titrating with the iron solution. Large amounts of aluminum and copper caused high results; however, amounts normally present in the soil had no effect. For the determination of total iron, fusion of the sample in a cast silver crucible has been suggested (8), because platinum crucibles containing an indefinite amount of iron are not suitable for decomposing silicates and organic matter in the soil. The perchloric acid digestion decomposes soil organic matter and has been successfully used in the determination of copper, zinc, lead, and
Cheng, K. L., and Bray, R. H., Soil Sci., 72,449-55 (1951). Goetr, C. A,, Loomis, T. C., and Diehl, Harvey, ANAL.CHEM., 22,798 (1950). Holmes. R. S.. Soil Sci.. 59. 77 11945). Pribil, R., and Matyska, B., Colleciton Czechoslov. Chem. Communs., 16,139 (1951). Robinson, W. O., Soil Sci., 59,7 (1945). Schwarzenbach, G.. and Heller, J.. Heln. Chim. Acto, 34, 576 (1951). Schwarzenbach,G., and Willi, A , , Ibid., 34,528 (1951). Shell, H. R., ANALCHEM.,22,326 (1950). FValden, G. H., Jr., Hammett, L. P., and Edmonds, S, SI., J . Am. Chem. SOC.,56, 350 (1934). Yoe, J. H., and Jones, L., ~ ~ N A LCHEM., . 16, 1 1 1 (1944). RECEIVED for review June 9, 1952.
Sccepted September 24, 1952,
Determination of Moisture in Oils and Greases R. Y. MEELHEIM AND J. N. ROARK Monsanto Chemical Co., Nitro, W . Va. HE Roberts and Levin ( 2 ) method for determining small Tamounts of water by distillation through a closed system to a receiver where the distillate, a water-solvent mixture, is titrated with Karl Fischer reagent has proved to be a valuable tool in determining moisture contents of materials which are immiscible with Karl Fischer reagent or react with it. However, it has been found necessary to distill large quantities of solvent for long periods of time, from 1 to 2 hours, in order to dry the solvent sufficiently, purge water from the sample and walls of the apparatus, and transfer all of the water to the receiver for titration. Such a serious limitation prevents the use of this method for routine control. To eliminate' this fault certain refinements have been made in the procedure which increase the accuracy, precision, and speed of the determination. These refinements are: the use of an efficient fractionation column; a method of heating the column, tubes, and condenser; and a better azeotrope former. The apparatus shown in Figure 1 accomplishes the above objectives and gives highly accurate and reproducible results. Much less time is required for an analysis using the refined apparatus.
might not be swept or flushed into the receiver, the distillatiori flask, fiactionation column, connecting tube, and condenser are sealed together with a minimum of bends in the path of the hot vapors. The column packed with glass helices affords sufficient fractionation to reduce greatly the amount of distillation necessary to recover all the mater in the receiver. Furthermore, by wrap; ping the top of the column and all of the connecting tube with electrical heating tape and asbestos insulation (see 8 and 9 in Figure l ) , the tube walls are maintained a t a sufficiently elevated temperature to ensure that the water will continue in a vapor state and be swept into the receiver for titration. Water is not circulated through the condenser but allowed to stand and reach its boiling point. This ensures a condensing surface for the distillate, which remains hot enough to prevent water from adhering excessively to the walls of the condenser. Experience has shown this condensing surface is adequate to condense the water as it enters the receiver. Thus, none is lost via the vent dryer.
REAGENTS
Karl Fischer reagent, 1 ml. equivalent to approximately 2.5 mg. of water Water-methanol standard, approximately 5.0 mg. of water per ml. Toluene, technical Pyridine, reagent grade Methanol, dry APPARATUS
The assembly is shown in Figure 1. I n order to prevent "dead" spots where a film of moisture
Table I. Typical Results Sahple"
A
B
C
D D D
Sample Weight,
H20 Added, G.
H10 Recovered, G.
HIO,
.... ....
0.0428 0,0404 0.0419
0.0422 0.0402
.... ....
G. ,,..
97.7 101.7 101.8
Propylene polymer.
.... ....
....
0.0403 0.0224 0.0225 0.0234
%
,...
0.0230 0.0221 0.0230
Approximate Analysis Time, Min. 30 30 30 30 30 30
V O L U M E 25, NO. 2, F E B R U A R Y 1 9 5 3
349 have fallen into receiver 15 for a t least 5 minutes. Turn on Powerstat 1 to a voltage high enough to heat the column and tubes to about the boiling point of toluene and continue to distill until the water in the condenser jacket has boiled for a t least 15 minutes. Turn off both Poiverstats. Read the volume on the watermethanol buret and titrate the excess Karl Fischer reagent in receiver 15 to a dead-stop end point. Reread the water-methanol buret to determine the volume used.
_1
Calculation. ( A ~
x
B
- c x D )100 = E
%H,O
where A = ml. of Karl Fischer reagent B = Karl Fischer reagent factor, grams of water per ml. = ml. of water-methanol solution D = water-methanol solution factor, grams of water per ml. E = weight of sample, grams
c
DISCUSSlON
Figure 1. A p p a r a t u s 1, 2.
3. 4. 5. 6. 7. 8. 9. 10.
11. 12.
13. 14.
15. 16. 17. 18.
18.
20.
Powerstats Distilling flask, I-liter Heating mantle, Glas Col Weighing-dropping funnel Fractionation column, length 25 inches diameter 15 mm. Glass helix packing, I/r-inch diameter ;urns Asbestos insulation Heating tape Water-methanol solution reservoir, capacity 2 liters Water-methanol solution buret, capacity 50 ml. Drying, tube, CaCh Karl Fischer reagent reservoir, capacity 2 liters CaC12 receiver vent Flask 500-ml., round-bottomed, 3-necked, electrode joint, vent Bbtldurn wire electrodes M a netic stirrer KaA Fischer reagent buret, capacity 50 ml. Condenser Ground-glass standard-taper connection
The sample container is attached to the distillation flask by means of a standard-taper joint which facilitates weighing and interchanging of containers. DETERMINATION
Pour 500 MI. of toluene through 8 25-Inch tower 20 mm. in diameter, filled with 8-mesh activated alumina, into distillation flask 3. If the apparatus has been used previously, this step may be eliminated by reusing the old solvent. Should the distillation flask and receiver be too full, they may be easily emptied by siphoning, Fill separatory funnel 5 x-ith sample [for grease samples the Roberts and Levin ( 2 )grease sampler is convenient], weigh, and insert in the standard-taper joint, 20, in place of the tower. Through the electrode glass joint in receiver flask 15, pour 25 ml. of dry methanol. Replace the electrode firmly. Turn on Mag-Mix, 17, and add an excess of Karl Fischer reagent from automatic buret, 18, until the “dead stop” potentiometer needle is permanently deflected to a reading of a t least 40 pa. if a micioammeter is used as the current-measuring device ( 1 ) . Turn on Powerstat 2, connected to heat distillation flask 3, and set the voltage sufficiently high to distill the liquid into the flask rapidly (1 or 2 drops per second). Heat until drops have distilled into receiver flask 15 for 5 minutes, then turn on Powerstat 1 to a voltage high enough to heat the connecting tubes to about the boiling point of toluene, and continue distilling for a t least 15 minutes or until the water in the condenser jacket, 19, has boiled a t least 10 minutes. Turn off Powerstat 1 and reduce the voltage of Powerstat 2 just low enough to stop distillation in flask 3. If all the Karl Fischer reagent has reacted, add more and continue the distillation until none is consumed by further distillation, then titrate the excess to a dead-stop end point ( 1 ) with water-methanol from automatic buret 11. When the end point has been reached read the volume of the Karl Fischer buret, add approximately 10 ml. in excess of the amount expected to react with the water to be distilled from the sample, and reread to determine the exact volume added. Open the stopcock in separatory funnel 5 , remove the glass stopper, and allow the sample to flow into distillation flask 3. Close the stopcock and replace stopper when the funnel has emptied. Viscous liquids may be added in this manner, as the weights are determined by difference. Raise Powerstat 2 sufficiently to start rapid distillation (one or two drops per second) and allow to distill until drops of distillate
The choice of solvent or azeotrope Eormer for use in this method was mentioned by Roberts and Levin ( 2 ) . However, for very small amounts of moisture it is very necessary that a highly efficient azeotrope former be employed. The writers found that in most cases toluene was more efficient and more easily dried than benzene. I t is miscible nTith most of the same substances as benzene, and forms an azeotrope with water which contains 13.5% water and boils a t 84.1 C. (the benzene azeotrope contains 8.8% water and boils a t 69.1” C.). Toluene boils at 110.6’ C. This is a sufficiently high temperature to prevent sorption of water on the walls of the apparatus. If the sample is not soluble in toluene or benzene, it will be necessary to employ a more suitable solvent. Roberts and Levin (2) used pyridine successfully with greases. ACKNOWLEDGMENT
The authors wish to express their appreciaticn to Davenport Guerry and J. F. Santrock for their suggestions regarding design of this apparatus. LITERATURE CITED
(1) Foulk, C. W., and Bawden, A. T., J . Am. Chem. Soc., 48, 2045 (1926). (2) Roberts, F. M., and Levin, H., ANAL. CHEhf., 21, 1553 (1949), RtcEivED
f o r review August 16, 1952.
Bccepted September 30, 1962.
CORRECTIONS Isolation of Olefins from Bradford Crude Oil K. van Xes has called attention to an article entitled “Olefinic Components of a Pennsylvania Crude Oil” [Haak, F. A., and van Xes, K., J. Inst. Petroleum, 37, 245-54 (1951)], which should have been mentioned in my article entitled “Isolation of Olefins from Bradford Crude Oil” [ANAL.CHEM.,24, 1551 (1952)]. The oversight is regretted. I had every intention to include it, since we had corresponded with Dr. van Nes about his work and I have a high regard for it. It is certainly true that the two papers supplement and support each other. R,E. PUTSCHER
Polarographic Studies of Some Organochlorosilanes In the article on “Polarographic Studies of Some Organochlorosilanes” [Abrahamson and Reynolds, ANAL. CHEM.,24, 1829 (1952)l the next to the last line under Procedure should read: ((treating a known concentration of hydrochloric acid dissolved E. A. ABRAHAMSON in pyridine.”
