ANALYTICAL EDITION
26
and the cover are washed, 4 drops of 0.1 per cent alcohol solution of dimethylaminobenzene are added, and the solution is titrated with 0.25 N sodium hydroxide to a slight pink color of the indicator. The number of cubic centimeters of 'acid required to dissolve the precipitate of calcium carbonate multiplied by 1.4 gives the per cent of CaO in the sample. Table I-Representative RZOS SAMPLEPresent Found Per cent Per cent 9.4 1 9.3
Analyses of Cementa
MAGNESIUM OXIDE Present Per cent
Found Per cent
CALCIUM OXIDE
Present Per cent
Found Per cent
5.0 61.8 62.0 64.0 64.5 1.1 8.9 2 8.9 61.7 61.9 10.4 3.3 3 10.5 1.5 62.5 82.7 9.3 4 9.2 a Acknowledgment is made to the Bureau of Standards, from whom the 4.9 1.1 3.1 1.5
analyzed samples were obtained.
Discussion of Method I n the calculation of results, for strict accuracy, the number of cubic centimeters of acid required to dissolve the magnesium hydroxide should be multiplied by 1.008 instead of 1, and the number of cubic centimeters of acid required to dissolve the calcium carbonate should be multiplied by 1.4018 instead of 1.4. However, since this method will be of use only for control work, where the highest accuracy is not required, the approximations given will be satisfactory. The fact that the results by this method are as near correct as shown in the above representative set of analyses is due to a balancing of errors. The loss of magnesium hydroxide in the filtrate is offset by the precipitate of calcium carbonate, due to the slight amount of carbon dioxide absorbed from the air, and to the presence of a small amount of sodium hydroxide not washed out of the precipitated magnesium hydroxide. After magnesium was determined, the solutions were filtered and the calcium determined by precipitation of the oxalate and titration with potassium permanganate. The results, expressed in terms of MgO, were 0.3, 0.3, 0.4, and 0.2 per cent, respectively, for samples 1, 2, 3, and 4. The slightly high results for calcium, in spite of this loss, must be due to the sodium carbonate remaining after three washings. I n order to cut carbonation oi the calcium to a minimum, the precipitate of magnesium hydroxide should be filtered in a room in which there are few burners, and the beaker and funnel containing the precipitate should be kept covered as much as possible. To see what would be the effect of filtering in the presence of an abundance of carbon dioxide, the following experiment was carried out: In two solutions, each containing 10 cc. of magnesium chloride solution (1 cc. = 2 mg. Mg) and calcium chloride equivalent to
Vol. 1, No. 1
300 mg. of CaO, the magnesium was precipitated as the hydroxide and the precipitates were filtered off with lighted Bunsen burners at full height on each side 10 cm. from the funnels.
In one case the beaker and funnel containing the magnesium hydroxide were left uncovered and the beaker was allowed to stand by one burner. In the other case both beaker and funnel were kept covered except while the funnel was being filled. The magnesium was determined as described above and the calcium present with the magnesium hydroxide precipitate was determined as the oxalate. The values obtained are given below: UNCOVERED
SAMPLE 1Mg.
Magnesium Magnesium equivalent of calcium
22 8 33
COVERED SAMPLE
Mg. 21.3 2.1
It is quite evident from these results that precautions should be taken to prevent carbonation. However, if due precautions are taken, no great error should be introduced, for even with the excellent chance for carbonation in the covered sample, the magnesium found was only 1.3 mg. higher than the amount present. I n a 0.5-gram sample of cement, this corresponds to a little over 0.4 per cent of MgO. The determination of iron and aluminum oxides by this method takes a little longer than by two precipitations with ammonium hydroxide, for when this method is used the first washing must be thorough enough to insure practically complete removal of calcium and magnesium. This is because the filtrate from the second precipitation contains ammonium hydroxide, which, if mixed with the original filtrate, will interfere with subsequent tests. The accuracy of the two methods should be about the same. This method for the determination of calcium and magnesium is much more rapid than the customary procedure of precipitating the calcium as the oxalate and the magnesium as magnesium-ammonium phosphate, particularly if a double precipitation of magnesium is carried out. I n this procedure no evaporation is necessary, and both calcium and magnesium are determined volumetrically with one set of standard solutions. However, it is not quite so accurate as the customary procedure, for calcium oxalate can be washed more thoroughly than can calcium carbonate, without danger of loss, and in spite of balancing errors, the results for magnesium are not so accurate as those obtained by the more tedious gravimetric method. This procedure should be of especial advantage for control work, where magnesium alone is determined. When extreme accuracy is not required, it should find a field of usefulness, also, when Rz03and calcium are to be determined.
X-Ray Quantitative Analysis of Tetraethyl Lead in Gasoline' R. .H. Aborn and R. H. Brown DEPARTMENT OF CHEMICAL ENGINEERING, MASSACHUSETTS INSTITUTE
-RAY methods have been applied successfullyto quantitative analysis in but very few instances and these have been confined largely to spectral absorption methods. The possibility that a mass absorption method might serve as a means of determining the amount of tetraethyl lead in gasoline was suggested to the writers by George Calingaert of the Ethyl Gasoline Corporation. The concentration range of tetraethyl lead in commercial
X 1
Received August 20, 1928.
OF
TECHNOLOGY, CAMBRIDGE, MASS.
gasolinesvaries from under 0.5 to 3 cc. per gallon (3.7854 liters), and an error in analysis under 0.1 cc. per gallon is desirable. With the experimental arrangement described below the method is capable of an accuracy of 0.1 cc. per gallon. With further refinements it is believed the precision can be increased to the accuracy required in commercial analysis. 0.1 cc. per gallon is equivalent to 1 part in 14,000 parts by weight. Such high sensitivity is possible only when the constituents (in this case solvent and solute) differ very widely
,
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 15, 1929
in absorbing power. It seems probable, however, that a modification of this method might be applied to other materials whose constituents differ less widely in absorbing power, provided the required sensitivity is not so high.
a X-RAY
TUBE
I
/LEAD
PROTECTIVE RESISTANCE SAMPLE CONTAINER
-
C A LVAN OMETER SHUNT
., SULPHUR INSULATOR
L---J
H.V.
IONIZATION CHAMBER
-
!
BATTERY OF 100 VOLTS
Figure 1
A diagram of the experimental arrangement is shown in Figure 1. All wires, batteries, and instruments were electrically shielded. A water-cooled molybdenum target diffraction type Coolidge tube, operating a t 35 kilovolts and 20 milliamperes, was found well suited for the work. The ionization chamber was of the Bragg type and the galvanometer was a Leeds and Northrup moving-coil type instrument with a sensitivity of 10-10 amperes. Specimen containers made from brass tubes having an inside diameter of 3.97 cm. with an effective length of 5.08 em. were found satisfactory. The capped ends contained 2.54 cm. diameter holes, over which 0.00508 cm. thick aluminum windows were placed. The standard solutions were made up from tetraethyl “fluid” of such a composition that 3 cc. of “fluid” contained
27
1.65 CC. of P b ( C Z H ~ ) Eight ~. samples were made up containing from 0.0 to 3 cc. of tetraethyl lead per gallon (3.7854 liters) using commercial gasoline as the solvent. Among the conditions which exert a marked influence on the shape of the curve will be the type of radiation and the thickness of specimen penetrated by the beam. Figure 2 shows two curves obtained under the above operating conditions. From these curves i t seems evident that: (1) The method holds distinct promise as an analytical tool; (2) the experimental conditions as outlined give practically straightline curves; (3) an accurate control of operating conditions is important. It was also observed that close current control is equally important, Among further refinements to increase the precision may be mentioned a high sensitivity resistance bridge in conjunction with an i o n i z a t i o n 4 chamber, or two ionization chambers bal- 2 a n c e d a g a i n s t each other, one for a standard specimen and the a 20 2 30 other for t h e “uncc known.” Figure 2 As the time required for each determination by this method may reasonably be anticipated t o be as short as 5 minutes, while the usual chemical method requires 40 minutes, a further practical and economic point is added to the value of this new method.
ti
I O
IS
CONC
Pb(ET)*PEI
CAL
Note on the. Estimation of Borate in Natural Waters‘3z Margaret D. Foster SURVEY, UNITED STATES GEOLOGICAL
I
N T H E examination of natural waters information on
the probable content of borates is sometimes desired. The Gooch m e t h ~ d involving ,~ the distillation of methyl borate, takes more time and requires more water than are usually available for the determination. It has been found satisfactory to use for such samples an adaptation of the wellknown qualitative test with turmeric. When all the details described below are followed carefully the results obtained are sufficiently accurate for the purposes of a general survey. Time has not been available to make a study of possible interfering substances or of the possibility that boron might be present in a form that would not react with the turmeric. It appears, however, that the quantity of borate in most natural waters is indicated fairly closely by the method described.
WASNINGTON,
D.
c.
has been repeatedly washed in water are dissolved in 500 cc. of alcohol. Filter before use. HYDROCHLORIC ACID SOLUTION-4 cc. of hydrochloric acid (sp. gr. 1.178-1.183) are added t o 96 cc. of distilled water. SALT SOLUTION-25 grams of sodium chloride and 25 grams of sodium sulfate (anhydrous) in 1 liter of distilled water. Procedure
Add 1 cc. of the hydrochloric acid solution and 1 cc. of the turmeric solution to 10 cc. of the sample in a small white evaporating dish. Evaporate to dryness very slowly on the steam bath. If the residue is golden, with no trace of pink, no borate is present.’ If it has a pink or rose tint, borate is present. The quantity may be estimated by comparison with standards prepared by evaporating to dryness Reagents very slowly known quantities of the borate solution, made up STANDARD BORATESOLUTION-(^) 0.16 gram of borax in 1 to a volume of 10 cc. with distilled water, to which 1 cc. of liter of distilled water (1 cc. contains 0.1 mg. BOs); (2) hydrochloric acid solution and 1 cc. of turmeric solution have 25 cc. of solution 1 diluted to 250 cc. (1 cc. contains 0.01 mg. been added. The standards may range from 0.000 to 0.50 mg. of BO,. Bod. TURMERIC SOLUTION-5grams of powdered turmeric which Standards containing 0.000, 0.0025, 0.0050, 0.0076, and 0.010 mg. of BOs show distinct differences in tint, and in samples 1 Received July 31, 1928. containing such quantities the BOa may be estimated to about 2 Published by permission of the Director, United States Geological 0.001 mg. Above 0.01 mg. the standards must have wider Survey. ranges-0.01, 0.03, 0.06, 0.10, 0.25, and 0.5 mg. of BO8 to a A m . Chem. J . , 9, 23 (1887).
