Analytical Distillation in Miniature Columns Performance under Total and Partial Reflux A. G . N E R H E I M and R. A. DINERSTEIN Research Department, Standard O i l Co. (Indiana), Whiting, Ind.
Performance data for miniature distillation columns are needed to select the best column and operating conditions for separating a particular sample. Columns should be evaluated under both total reflux and actual operating conditions. Such a study has been made of typical commercially available columns. i t total reflux, the Hjper-Cal column has a lower height equal to a theoretical plate than concentric-tube and spinning-band columns. The spinning-band column has the lowest holdup and pressure drop; i t is more efficient when a tight band is used and rotated at the optimum speed. Reducing the pressure to 300 mm. decreases plates for all columns at moderate but not at low throughput. Studies at partial reflux reveal the importance of holdup. Although the Hyper-Cal column has more plates, the spinning-band, having lower holdup, may give a better separation of a small sample. I n such cases, high reflux ratio is undesirable. Equivalent separations have been obtained in both miniature and macro Hjper-Cal columns operated under like conditions.
also compared a t partial reflux. Conventional properties (number of theoretical plates, holdup, and pressure drop) were determined under total reflux a t atmospheric and a t 300-mm. pressure. Interrelationships among these properties were revealed by studies a t partial reflux. h miniature column and a macro column of similar design s e r e compared by distilling identical samples in both. EQUIPMENT AND MATERIALS
Miniature columns of three designs were tested: Column Spinning-hand Concentric-tube Hyper-Cal
Diameter, Rlm.
5 8
H E R E is a gron-ing need for fractional distillation of the products of small-scale experiments that yield 50 ml. or less. Equipment for such distillation has become available commercially, and its operation has been described ( 2 3 ) . However, to select the best distillation column and operating conditions for separating a particular sample the performance characteristics of the available columns must be knov-n. Although evaluations of experimental miniature columns have been reported, little has been published on commercially available columns. T h e published reports about both are concerned mostly n-ith performance under total reflux; selected examples are shown in Table I . I n contrast with research on macro coliiinns for the laboratory, no extensive stildl- has been made of the characteristics of miniature columns under partial refluxthe conditions under ivhich they actually operate. I n the present study, the performance of three types of commrrrial columns n-as compared at total reflux; two of them were
Table I.
Details of the construction of these columns have been described ( 2 3 ) . Of the three types of columns, only the Hyper-Cal is commercially available in macro size; that used for comparison was 13 mm. in diameter and 120 cm. long (16). For studies a t total reflux, two mixtures were used: H nMole
Diameter, film.
Length, Cm.
Band Speed,
R.P.11.
Throughput, 311. per HETP, Hour Cm.
Spinning-Band Column Podhielniak, I n c , ( I 7 ) Lesrsne, Lochte (20) Zuiderweg ( 2 4 ) 3lurray (12) Crutliirds, Jones, Seyfried (6) Crozier, Robert, Rousseau (4)
2500 1000 3600
60 ..
GO
4000
100
3.8
110
2300
20
3.2
26
0.49
J
GO
6
37.5 c i0 75
ii
G
G.5 8
40
1 0 2.5 1.3 1.2
Hyper-Cal Podhielniak, I n c . ( I ? )
8
..
30
Concentric-Tube Column
Naragon, Lewis ( 1 4 ) 8" Podhielniak, I n c . ( 1 7 ) 8" 14a Donnell. Kennedy (6) Annular space, 0.75 m m .
30 00
76
..
..
77 20 30
0.35 0.67 0.53
10 12
~
70
Relative ~ Volatility ~ ~ 760 mm. 300 mm.
1.07 (1) 1.023 (8)
1.05 (9) ...
The mistures Tvere prepared from Phillips Pure Grade hydrocarbons that were further purified by percolating through silica gel and distilling through a Hyper-Cal column 25 mm. in diameter and 420 em. (14 feet) long. Analysis by mass spectrometer showed no impurities in the purified hydrocarbons. The first mixture was used for test,ing columns having fewer than 100 theoretical plates; the second, for more efficient' columns. Only the first mixture was used for testing a t 300-mm. pressure. For studies a t partial reflux, three five-component mixtures of the same purified commercial hydrocarbons were used: Boiling Point, C. Cyclohexane-benzene azeotrope (11 ) Brnzene n-Heptane 3Iethylcyclohexane n-Octane
77.7 80.1
98.4 100.9
125.7
Each mixture included 2.5 ml. of the azeotrope and of benzene, but differing amounts of n-heptane, methylcyclohexane, and noctane in the proportion of 15 t o 15 t o 100. For comparing miniature and macro columns, the eight-carbon portion of a mid-continent virgin naphtha was used. PROCEDURE
Selected Published Data on Miniature Columns
Reference
60
90
8
n-Heptane and methylcyclohexane n-Heptane and 2,2,4-trimethylpentane
T
Length, Cm. 90
Throughput was measured in terms of drops of reflux from calibrated condenser drip tips; the range selected for test was typical of the usual operations in the laboratory. The Hyper-Cal columns were first preflooded t o wet the packing completely. Except where otherwise noted, the spinning-band columns were tested with a tight-fitting band rotated a t 2000 r.p.m. I n studies a t total reflux, the number of theoretical plates, pressure drop, and holdup !?ere determined as a function of throughput. The number of t'heoretical plates was determined from the composition of samples taken from the head and flask after refluxing 200 ml. of a test mixture for a t least, 5 hours to reach a steady state, which was the point a t which further refluxing gave no increase in the number of plates. Head samples were about 0.05 ml. Compositions of the samples were calculated from refractive indices. For mixtures of n-heptane and methylcyclohexane, the indices were measured t o 0.0001; for n-heptane and 2,2,4-trimethylpentanej to 0.00002. Theoretical plates m r e calculated by means of the Fenske equation ( 7 ) . Pressure drop was measured during plate testing with a U-tube manometer containing dibutyl phthalate. Holdup was determined (6) by 1029
~
~
ANALYTICAL CHEMISTRY
1030
ITHEORETICAL
._"
refluxing 25 ml. of a 25% solution of a high-boiling oil in n-heptane and determining the oil content of the flask from refractive index. Studies a t partial reflux were patterned after the work of Rose and O'Brien (20)who studied the effects of holdup, reflux ratio, and initial total reflux. The five-component mixture was distilled in 90-cm. spinning-hand and Hyper-Cal columns a t a throughput of 20 ml. per hour. Reflux ratios were based on throughput measured a t the top of the column and do not take into account the higher reflux ratios a t the bottom caused by heat loss through the walls. T h e primary measure of performance was the separation of n-heptane and niethylcyclohexane; the lower boiling components minimized the effects of initial total reflux on this separation. The composition of selected fractions was calculated from refractive index and fluorescent indicator adsorption (S). Three sample sizes a t three reflux ratios gave nine tests on each column; duplicates agreed acceptably. For comparison of miniature and macro columns, the eightcarbon naphtha was distilled in two columns (8 mm. X 90 cm. and 13 mm. X 120 em.) under conditions selected to give equal theoretical plates, charge-to-holdup ratio, and reflux ratio.
I2C
m W
I00
U
-I
a
8C
S P l N N I NG-BAND I
I
40
R ,
1
I
C-T ,
I
24
PRESSURE DROP 20 m
-
16-
r
Three types of studies were carried out a t total reflux. Conventional properties were determined a t atmospheric pressure : theoretical plates and pressure drop were determined a t 300-mm. pressure; and the effects of hand fit and speed of rotation on the separating power of a spinning-band column were studied a t both pressures. The detailed data, Tvhich will he made available to those interested, have been summarized in four graphs. Tests a t total reflux and atmospheric pressure are summarized in Figure 1. The number of theoretical plates decreases with
-
E 12E 08
r
I
CONCENTRIC-TUBE
w
O 4 I
0'
0
0
SPINNING-BAND
I
1
20
40
I
80
60
II
THROUGHPUT, m l . 1 hr. Figure 2. Performance at total reflux and 300-mm. pressure Dashed lines taken from Figure 1
.T H E O R E T I C A L P L A T E S
ft
-- -
63
STUDIES AT TOTAL REFLUX
l40 -
1
PLATES
140
H Y P E R -GAL
AT CONSTANT T H R ~ U G H P U T ~
120
cn W
0
I
k
IW
LOOSE
W
fn 0
a
." 1.2
iPRESSURE
s
LOOSE\
I4 0
(300mm.l
u +u
DROP
0
IO
20
30
40
50
100
THROUGHPUT, ml./hr. Figure 3.
0.2 SPINNING -BAND
01 6
1
I
I
I
I
I HOLDUP
.I
A+-/-
HYPER - C A L
SPINNING -BAND
0
0
20
40
60
80
THROUGHPUT, ml./hr. Figure 1. Performance at total reflux and atmospheric pressure
100
300
400
500
Effect of spinning-band fit on performance
increasing throughput. Pressure drop increases a t a greater rate in the packed column than in the two unpacked columns. Holdup is not greatly affected by increasing throughput above 30 ml. per hour. The Hyper-Cal column has the largest number of plates, pressure drop, and holdup. Either the height equal to a theoretical plate ( H E T P ) or the efficiency factor ( l e ) ,obtained by dividing throughput by holdup per plate, can be used to compare the columns a t constant throughput. D a t a for 20 ml. per hour are: Column Spinning-band Concentric-tube Hyper-Cal
CONCENTRIC-TUBE
200
OPERATING T I M E , hours
HETP, Cm. 1.1 0.85 0.74
Efficiency Factor, Plates per Hour 860
680 530
Efficiency factor gives inadequate emphasis to number of plates; the spinning-band has the highest factor because of low holdup. Columns of the same type, especially those with packing ( d l ) , differ widely in separating poFer. Three Hyper-Cal columns, 8 mm. in diameter and 60 cm. long, gave HETP values a t 20 ml. per hour of 0.65, 0.70, and 0.85 cm. Small variations in pack-
V O L U M E 28, NO. 6, J U N E 1 9 5 6
1031
ing cause differences in H E T P as well as in flood point, holdup, and pressure drop. Results of testing the columns a t 300-mm. pressure are shown in Figure 2. The number of theoretical plates is compared with data a t atmospheric pressure. A t this lower pressure the columns have a t least as many plates at lower throughput but fewer a t higher throughput. Of the three columns, the spinningband is most adversely affected by reducing the pressure a t high throughput. Greater separating power of packed columns at reduced pressure (13, 1 5 ) may be due to increased diffusion in the vapor phase normal to the interface ( 2 ) . A decrease in efficiency a t higher throughput may be caused by reduced contact time. The scatter of plate-test data for the Hyper-Cal colunin a t low throughput may result from the high relative volatility of the test mixture. Incomplete wetting of the packing may have caused the group of low values a t 20 ml. per hour. Reducing pressure to 300 mm. increases the pressure drop in the Hyper-Cal column much more than in either of the other columns and lowers the flood point proportionately:
speeds cause widely varying results having a downward trend. A decrease in throughput lowers the optimum speed. Similar results have been observed a t 300-mm. pressure. A loose band also shows an optimum, but a t a higher speed. When the shaft connecting the band and the magnetic drive was shortened froin 35 cm. to 25 cm., high speeds resulted in higher efficiencies, more reproducible data, and less vibration. A t a critical rotational speed below 1000 r.p.m. (%$), separating power rises as vapor diffusion is increased by turbulence due to the rotating band. Increased column efficiency resulting with a tight band and a t high speeds may have a common cause-namely, increased agitation in the liquid phase. Reduction of pressure does not alter the way either band fit or speed affects column efficiency, despite the increase in vapor velocity. Agitation in the liquid phase is also believed responsible for efficiencies higher than calculated for the rotary concentric-tube column ( 2 2 ) . 1.50
Flood Point, M1. per Hour 760 mm. 300 mm. 550 380 300 270 430 230
Column Spinning-band Concentric-tube Hyper-Cal
1.48
The effect of band fit on the separating power of a spinningband column is shown in Figure 3. At both atmospheric and 300-mm. pressure, fewer plates are obtained with a loose bandi.e., one that rotates freely in the column n-hen turned by hand. A tight band is shown to become loose during 1 month of operation; thus, any tests of a tight band requiring several days n-ill introduce a secondary effect of change in fit. The effect of increasing the speed of band rotation a t atmospheric pressure is shown in Figure 4. With increasing speed, the number of plates rises to a maximum, beyond which higher
20
1.46
C
I40
I20 IO0
0:
g-
0 80
W I T H CONVENTIONAL BAND SHAFT
WITH SHORTENED SAND S H A F T
W
1
60
I
1.40
0
z 0
m
2
4
6
8
DISTILLATE,ml.
Figure 6. comparison of miniature columns using synthetic mixture Charge, 15 nil.; reflux ratio, 40 t o 1
0 Boiling point, Hyper-Cal zooc
40CO C
2000
B A N D SPEED,rprn
Boiling point, spinning-band
4000
B A N D SPEED, r p m
Figure 4. Effect of spinning-band speed on performance Numerals are throughput in ml. per hour.
y E. zg > W
2.30
=z W a
+z W-
z
a n W
1.15
I-
L I
c ~
0
2000
40OC
B A N D SPEED, rp.m.
Figure 5.
Heating effect of spinningband
0
20 40 60 80 VOLUME 'le n - HEPTANE IN DISTILLATE
100
Figure 7. Comparison of miniature columns at partial reflux
ANALYTICAL CHEMISTRY
1032 The optimum speed may be caused in part by addition of heat of friction to the column. Heat generated by the rotating band increases throughput a t constant heat input to the flask as shown in Figure 5 . T h e optimum may then be the point a t which increased liquid mixing is offset by loss of equilibrium through excessive heating; for a lower throughput, it should occur a t a lom-er speed. L'ibration can also limit the advantages of high speed; it can be minimized by proper alignment of the band and column ( 2 3 )as well as by shortening the band shaft. Optimum speed has also been attributed t o back-diffusion in the liquid phase ($4). STUDIES AT PARTIAL REFLUX
I n studies a t partial reflux, the three five component mixtures were distilled a t three reflux ratios in a spinning band and a Hyper-Cal column. Results with a pair of identical samples at a reflux ratio of 40 to 1 are shown in Figure 6. The spinning band column gave better separation, as shown by the lower refractive index of the heptane concentrate, A , and higher index of the methylcyclohexane, B. Results of all distillations are summarized in Figure i . The tests are grouped according to the volume of n-heptane and methylcyclohexane in the sample because the sharpness of separation between two components in a mixture depends on the total amount of the two components, rather than on the total amount of sample ( 2 0 ) . The length of each bar represents the heptane content of fraction A . -4s the amount of the com ponents decrease, separation becomes poorer in both columns increasing holdup-to-charge ratio has a detrimental effect.
ZQ c
X W
0
142
W
1 F 0
a
a
LL W
a
Column Dimensions
8 m m . X 9Ocm. 13 mm. X 120 c m . 25 mm. X 120 c m .
Throughput, TheoretHoldEfficiency M I . per ical H E T P , up, Factor, Plates Hour Plates Cm. hI1. per Hour 107c of Flood Point 105 43 0 813 140 100 0 82 280 152 0 79
5 16 50
860 870 850
5 28 67
830 1090
Equal Theoretical Plates
8 m m . X 9Ocm. 13 m m . X 120 c m . 25mm. X 120cm.
28 270 470
113 113 113
0.80 1.08 1.06
930
Although high reflux ratios have been found to aid separation of 10 ml. of components, they offer little or no advantage in separating smaller volumes. K i t h 2.30 ml., the lower reflux ratios gave the beEt separations. Changing reflux ratio had little effect a t 1.15 or 4.60 ml. Similar effects have been observed in binary systems (19). The findings in terms of the separation of n-heptane and methylcyclohexane have been verified by the corresponding data for separating methylcyclohexane and n-octane. T h e tests a t partial reflux provide a basis for selecting a column and operating conditions for a given sample. Components pres ent to the extent of 4 ml. can be separated best by a Hyper-Cal column. K h e n 1 to 4 ml. of the components are present, the! would be separated best by a spinning band column a t a reflux ratio no higher than 40 to 1. Smaller volumes of components can be separated as ne11 by either column a t a low reflux ratio COMPARISON OF MINIATURE 4ND MACRO HYPER-CAL COLUMNS
1.44
'
Table 11. Comparison of Miniature and Macro Hyper-Cal Columns at Total Reflux
1.40
L
I . 3 80
20
40
DISTILLATE
60
, VOL.
80
CONC LU S I 0 3
e/e
Figure 8. Comparison of miniature and macro columns using eight-carbon naphtha Charge, ml. Throughput, ml. per hour Reflux ratio Distillation time, hours
D a t a at total reflux for a miniature Hyper-Cal column and t r o macro columns are given in Table I1 on the basis of equal fraction of flood point and equal theoretical plates. .It equal fractions of flood point, the columns have nearly equal H E T P values. At equal theoretical plates the macro columns have much higher efficiency factors; the! had to be operated a t higher throughputs because they are both larger in diameter and longer. Relative charge sizes can he estimated from the holdup data. Distillation of identical samples in the miniature and the 13-mm. macro columns, operated a t equal theoretical plates. gave the distillation cuires in Figure 8. Equivalent separation. \yere obtained.
hliniature 40 28 56:l 84
Macro 220 270 56: I 55
Holdup can be more significant than theoretical plates. With 2.30 nil. of the components to be separated, the spinning band column, having 82 theoretical plates a t total reflux and a holdup of 1.9 ml., gave a better separation a t the same reflux ratio than the Hyper-Cal column having 122 plates b u t a holdup of 4.6 ml. With the smaller volume of the components, the holdupto-charge ratio was too large for either column to show an advantage and the separations were poor. T h e larger volume enabled the greater number of plates of the Hyper-Cal to take effect. Thus, low column holdup can offer an advantage in a limited range of component volumes.
The separating parer of niiniatu1e columns is equal to that of macro columns n-hen they are operated a t equivalent conditions. I n both, the effects of number of plates and reflux ratio on separation depend on the amount of the components to be separated. Reducing pressure to about half an atmosphere decreases plates a t moderate but not a t lov throughput. Future studies will cktermine thp effects of lower pressures. ACKXOW LEDGMENT
The authors thank J. C. JTinters and IV. W.Sanders for their helpful suggestions and F . S.Jones for the data on macro columns. LITERATURE CITED (1) Beatty, H. A, Calingaert, G., Ind. Eng. Chem. 26, 504-8 (1934). (2) Byron, E. S.,Bowman, J. R., Coull, J., I b i d . , 43, 1002-10 (1951). (3) Criddle, D. W., LeTourneau, R. L., ANAL.CHEY. 23, 1620-4
V O L U M E 2 8 , N O . 6, J U N E 1 9 5 6 (1951) ; Am. Soc. Testing Materials, Philadelphia, Pa., Standards, Pt. V, RIethod D 1319-54T. (4) Crozier, A . , Robert, L., Rousseau, J. C., Rev. inst. frane. pe'trole
et Ann. combustibles Ziquides 8 , 79-81 (1953). (5) Cruthirds, -1.V., Jones, W.C., Seyfried, W.D., Oil Gas J . 48, KO.41. 117-19 (1950). (6) Donnell, C. K., Kennedy, R. AI., I n d . Eng. Cheni. 42, 2327-32 (1850). (7) Fenske, 11. R.. I b i d . , 24, 482-5 (1932). (8) Griswold, J.. I b i d . , 35, 247-51 (1943). (9) Hawkins, J. E., Brent, J. A , Jr., I b i d . , 43, 2611-21 (1951). ESG.CHEM.,ANAL.ED. 10, (10) Lesesne, S.D., Lochte, H. L., IXD. 450 (1938). (11) RIarschner, R. F., Cropper, W.P., Ind. Eng. Chent. 38, 262-8 (1946). (12) lIurray, K. E., J . Am. Oil Chemists' Soc. 28, KO.6 , 1-5 (1951). (13) AIyles, AI., Feldman, J., Wender, I., Orchin, RI., I n d . Eng. Chem. 43, 1452-6 (1951). (14) Karagon, E. A , , Lewis, C. J . , IND.ENG.CHEX.,ANAL.ED. 18, 448-50 (1946).
1033 (15) Peters, AI. S., Cannon, 11. R., I n d . Eng. C h e n . 44, 1452-9 (1952). (16) Podbielniak, Inc., Chicago, Ill., Bull. A-2 (1953). (17) Ibid., A-3 (1953). (18) Podbielniak, IT. J., IBD.ENG.CHEY.,ANAL.ED. 13, 639-45 (1941). (19) Rose, Arthur, Johnson, R. C., Williams, T. J., Chem. Eng. Progr. 48, 549-56 (1952). (20) Rose, Arthur, O'Brien, 1'. J., Jr., Ind. Eng. Chem. 44, 1480-6 (1952). (21) Rose, Arthur, Rose, E . , in "Technique of Organic Chemistry," vol. IV, p. 68, A. Weissberger, ed., Interscience, New York, 1951. (22) Willingham, C. B., Sedlak, V. A . , Rossini, F. D., Westhaver, J. W., I n d . Eng. Chem. 39,706-12 (1947). (23) Winters, J. C., Dinerstein, R. A., ASAL. CHEM.27, 546 (1955). (24) Zuiderweg, F. J., Chem. Eng. Sci. 1 , 174-93 (1952).
RECEIVED for review M a y 26, 195.5. Accepted hlarch 14, 1956. American Petroleum Institute, Refining Division, St. Louis, M o . , May 1955.
Determination of Trace Elements in Titanium By Neutron Activation Analysis W. A. BROOKSBANK, JR., G . W. LEDDICOTTE,
and
S. A. REYNOLDS
Analytical Chemistry Division, O a k Ridge National Laboratory, O a k Ridge, Tenn.
A-eutron activation analysis can be used to determine microgram and submicrogram concentrations of many elements when these elements appear as impurities in titanium and its allojs. When applied to a specific element, the activation analysis method depends upon the formation of an artificial radioisotope of that element h: a nuclear-particle bombardment. It is a specific arid sensitive method of analysis and is uniquely free of contamination difficulties. Neutron activation analj sis methods have been devised for the determination of trace amounts of tungsten, chlorine, vanadium, nickel, copper, manganese, and silicon in titanium, its allojs and compounds. Seutron activation has been used as a qualitative analysis method to detect the presence of other trace elements. Some results of these assaj s are reported.
E U T R O S activation analysis has been applied successfully of impurities to tlie determination of microgram in titanium metal and its compounds. This study is concerned v i t h certain of these impurity determinations and the general for each application. activation allalysis have of T h e theor\, sild been cIex~1,ibed( 1 , 4, 6, 7 ) . T h e results of the analyses reported in this p:iper Tvere obtained by methods similar to those used in the analytical service program a t the Oak Ridge Sntional used L:iborator!- (6). The natural uranium-graphite reactor to activate the samples. The predominant reaction occurring in :i reactor of this type is the simple capture of thermal neutrons, the (n,?) reartion. Other nuclear reactions such as ( n , p )arid ( T I ~ Q )can also occur; hovevcr, these are less prominent and can usually be disregarded.
Table I s h o w the limits of detection for certain elements whose concentrations in titanium are of interest. The microgram value refers to the practical limit of measurement and is defined as that \\eight of the element nhich nil1 produce at least 40 beta disintegrations per second (or equivalent) of radioisotope Ti-hen irradiated for some time interval in a reactor such as the O R S L : graphite reactor (flux = ~ 1 0neutrons ' ~ per sq. em. per second). The time is that time required for an irradiation to go to "saturation" or 1 month, whichever is shorter. The limits of measurement can be extended downward by the use of the higher neutron flus, neutrons per sq. cm. per second, of the ORSL l o x intensity test reactor. I n the anal) ses repor ted herein. both quantitative and qualitative determinations are considered. I n the quantitative determinations, the uiiknoxm samples were usually ana1y.d for a single element : 11-hereas the qualitative analyses R ere concerned with any radioactivity induced in the sample. The techniques of analysis are described beloiv. Comparative Samples. I n all the assays described, the comparative method of analysis T I ~ S used ( 2 , 2, 7 ) . Keighed amounts of pure elenlellt or conlpound of the element xere irradiated along with the unknown sample in order to make a comparison of the activity of the induced radioelement(s). Comparative standards were not used in the qualitative studies. ~~
Table 1. .kctivation .knalysis Limits of XIeasurement for Certain Elements Element
-4ctivation analysis has been applied to the determination of impurities in elemental titanium and titanium oxide and may be applied to alloys or other compounds. Titanium is suitable for activation analysis because of its low activation cross section and the short half life of the radioactivity produced (5.8 minutes) ( 5 ) .
a
Half Life-
Radiations"
38 m P %Y 27 d EC.Y P, Y 2.6 h 47 d 8, Y co coco 8, 7 5 . 3 3' ?ii Xias ? >Y 2 . 6 I1 c11 Cue4 EC, 8 , Y 13 h Xb SbPdm 6.6 m IT, e Y i0 LIogQ 8. Y 67 h Ta Tal82 ? #Y 117 d 1%TT-187 25 h 8, 7 A1 .$I18 2.3 m 8. Y T' \-s2 3.7 m 8, I Si Si31 2.7 h ? #7 Information obtained from Table of Isotopes (6). c1 Cr hIn Fe
EXPERIMENTAL
Radioactivity Produced" c13s Crj' .\1n 56 Fe5Q
Liniit of .\Ieasurement,y 0 03 0 2 0 0001 2.0 0.02 2 0
0 007 10-100 0.1 0.007 0 003 1.0 0.05 2.0
