129b (X1112) containing c = 0.094, a n d S = 0.224. The carbon percentages obtained in 12 determinations for each of two series are p r e s r n t d in Table IV. X 3-inch length of the lead dioxide preparation was uwd in the Fleming zinc jar B-1 of The saniple m-eight vias Figure 2 . 0.9091 g a m . The oxygen flon was continuou., a t a rate of 0.4 liter per minute. The flushing time n a s 5 minutc-, as measured from the moment combustion ceased. h faint giay ijand, 3 l S inch in height, \?ab tliaccrn;iLlt. in the lead dioxide after the fird s r i e s nas completed. Tliis 11a‘ iiioie dibtinct and slightly highu upon completing the second. The gi ny hand 11R S sharply defined, and denoted the nniount of absorbent m hich effectcstl the tomplete removal of SO2. CONTAINER DIAMETER
Eqieriiiients Tx-ith containers of various dianietm for t,be lead dioxidecoated grain? shon-ed that a n inside diametcr oi 1 inch \\-as desirable for both the gixviinetric and eudiometric nietliod~. For the latter n 2-inch
Table IV,
Determination of Carbon in Sulfurized Steel
Carbon Percentage C1144“ NBS Sample 129b 0.096 0 096 0.486 0.486 0.096 0 096 0.486 0.486 0.096 0 096 0.486 0.486 0.096 0 096 0.489 0.486 0 099 0 096 0.483 0.483 0.486 0.489 0 093 0 096 Means 0.486 0.096 Sample of free machining steel; average values were C = 0.485, S = 0.32. Q
length of the material betneen t n o glass ~vool plugs 1\89 satisfactory. Oxygen flow rates in this nicthod n-ere varied from 0.5 to 1.0 liter per minute. A crude inverse square relation appeared to exist between the inside diameter and the length of the gray band when first discerned. Hence the service life of a charge should be most satisfactory when small diameters are avoided. Satisfactory use of a 1-inch diameter column in the eudiometric
method may be attributed to the high chemical reaction activity with SO%, and compensations such as smaller combustion samples and the greatly reduced critical flushing times which are caused by high oxygen flow rates. LITERATURE CITED
(1) Johnson, C. M., “Chemical Analysis of Special Steels, Steel LIaking Alloys, and Graphites,” 2nd ed., p. 224, \Tiley Sew York, 1914.
(2) Lundell, G. E. F., Hoffman, J. I., Bright, H. A., “Chemical Analysis of Iron and Steel,” p. 168, Wiley, New York, 1931. ( 3 ) Mellor, J. W., “A Comprehensive Treatise on Inorganic and Theoretical Chemistry,” 1-01~VII, p. 689, Longmans Green, S e w York, 192T. (4) U. S. Steel Gorp., “Methods of the Chemists of Subsidiary Companies of the United States Steel Corporation for the Sampling and Analysis of Pig Iron,” 3rd ed., pp. 115-16, Pittsburgh, Pa., (1934). ( 5 ) U. S. Steel Corporation, “Sampling and Analysis of Carbon and Alloy Steels,” p. 47, Reinhold, New York, (1938). (6) Ibid., p. 48. RECEIVEDfor review June 22, 1961. Accepted January 31, 1962.
Determination of Hydrogen in Calcium by Vacuum Fusion D T. PETERSON Institute for Atomic Research and Deparfment o f Chemistry, lowa State University, Ames, lowa
V. G. FATTORE Sicedison S. p. A., Centro Sfudi e Ricerche, Bollate, Milan, Italy
b
A rapid simple method for the determination of hydrogen in pure calcium i s presented. Hydrogen was extracted b y a vacuum fusion technique using a tin bath a t 670” C. to reduce calcium volatilization and to increase the speed of hydrogen evolution. The hydrogen content was determined b y measurement of the pressure of the gas collected in a known volume. Samples containing from 200 p.p.m. of hydrogen up to almost pure calcium hydride were successfully analyzed. The precision of the results was always better than 4y0.
T
coiiyentional procedures for determining hydrogen in metals are the vacuum fusion method with or without a metal bath and the hot vacuum extraction method. These procedures I\ ere developed primarily for the determination of hydrogen in steel but have been applied successfully to FIE
many metals. 4 large number of papers dealing with these techniques is available in the literature and several authors (1, 5 ) have summarized the work done on this subject. Difficulties arise in the determination of hydrogen in the alkali and alkaline earth metals because of the volatility of these metals. Several modified procedures have been introduced. Mallett, Gerds, and Griffith ( 4 ) determined hydrogen in magnesium, magnesium-lithium alloys, and lithium by the vacuum fusion method in which a tin bath a t 450” C. mas used. Bergstresser and Xaterbury ( 2 ) did the same determination on massive lithium hydride n ith an analogous technique but using a lead bath a t 600” C. On powdered samples of lithium hydride, Frazer and Schoenfelder ( 3 ) employed successfully a mercury bath a t 400” C. KO analyses have been reported for hydrogen in calcium and no procedures have yet been advanced for this deter-
mination. During this investigation the hot vacuum extraction method was tried, but unsuccessfully, because hydrogen is evolved with significant speed only a t a temperature a t which the calcium volatilization is too rapid for a n accurate analysis. The use of a tin bath under the appropriate conditions gave good results. No standard samples Tvere available to be analyzed to check the method but the results obtained by adding hydrogen to different specimens indicated that all the liydrogen is completely evolved. APPARATUS
The vacuum fusion apparatus consisted of a furnace section and a n analytical section. The furnace section included a resistance furnace, a Vycor tube containing a tin bath and a loading tree capable of holding six samples. The tin bath was 40 to 50 grams of Baker analyzed reagent tin. A short quartz tube which was closed at one end and which fitted snugly in the Vycor VOL. 34, NO. 4, APRIL 1962
e
579
Table 1.
Analysis of Calcium Metal and Calcium Hydride for Hydrogen
Weight,
Sample
Mg.
37.95 99.10 110.35 71.65 87.55 88.05 41 .OO 66.00 67 30 60.20 64.85 89.05 68.65 42.95 37.45 27.15 36.50 51.65 31.45 17.35 31.75 35.05 20.20 12.85 2.25 4.20
No. 1
KO.2
so.
3
No. 4
so. 5
No. 6
.5 .0.5
3.05
2.90
Hydrogen Wt. % 0.0222 0.0224 0.0214 0.0218 0.0219 0.120 0.118 0.108 0.116 0.116 0.276 0.268 0.278 0.286 0.430 0.435 0.423 0.413 0.805 0,810 0.812 0.820 0.835 4.48 4.45 4.60 .~ 4.55 4.83 ~
~
Hydrog y
No. 1
Mg.
FT.t. %
42.65
0.175
2
36.10
0.179
3
44.10
0.182
4
28.20 38.50
0.179 0.181
5
Arithmetical mean 0.179 wt. 7% Relative std. dev. 0.015 Relative error $0.011
tube, contained the tin. Samples were dropped into the tin bath from the loading tree by a magnetic pusher. The analytical section consisted essentially of the collection volume and a McLeod gage. Hydrogen evolved in the furnace section was pumped by a two-stage mercury diffusion pump into the collection system. The collection system had an auxiliary bulb which allowed the volume to be increased from 485 to 3865 ml. The collection system held 2 X mole of gas a t the maximum pressure of 1000 microns. The hydrogen was measured by a pressure measurement. Precision of the pressure measurement was o.3y0 a t 2 X lo-' mole and 1.5% a t 1 X 10-6 mole. Precision of the calibration of the larger collection volume was 0.1% and of the smaller volume was 1.0%. The quantity of hydrogen collected was therefore known with a precision from 0.4 to 2.5y0. All joints were 580
ANALYTICAL CHEMISTRY
Relative Standard Deviation
0.0219
0.018
0.116
0.039
0.277
0.027
0.429
0.026
0.816
0.014
4.58
0.033
0.442
Table 11. Analysis of Sample Charged to 0.1 77 Wt. % Hydrogen
Weight,
Arithmetical Mean
sealed with Apiezon W wax and the stopcocks were lubricated with DowCorning high vacuum grease. Specimens of the collected gas xere examined by gas spectrographic analysis and analyzing for hydrogen to see if some gas other than hydrogen was extracted from the sample. No significant quantities of impurities were found by mass spectrographic examination and the hydrogen determination showed that the gas extracted from the sample was over 98% hydrogen. PROCEDURE
The samples to be analyzed (2 to 200 mg. according to the hydrogen content) were taken in a glove box filled with argon. The samples were from specimens of triply distilled calcium which had been charged with pure hydrogen and melted in a stainless steel capsule. This resulted in a specimen of uniform composition from which samples were prepared by machining off the stainless steel capsule and sawing sections from the solid calcium metal. Analysis of the calcium metal showed the following amounts of impurities: magnesium, 300 to 350 p.p.m.; carbon, 70 to 100 p.p.m.; silicon,
