typical output for the second stage 5hown in Figure 2B. Thi\ indicates the minimum time of analysis and the olicrating parameters-temperature, flow, column length, per cent substrate, and inlet pressure-required to produce the minimum time of analysiq. The final result is illustrated by the chromatogram shonn in Figure 3. This chromatograni was obtained under the conditions prescribed by the computer, with the exception that the liquid loading was 10% rather than lo.@& This accounts for most of the discrepancy between the measured analysis time and the predicted analysis time. The use of a computer provides a means of efficiently abstracting the information content of the original data, checking it for consistency and storing it in a form that is convenient for future use. The full benefits of the method are on11 realized when, as in process control work, the time of analysis must be minimized. A\
is
N O M E N C L A W RE
B
=
longitudinal diffusion coefficient
BO C,
C,O Cz
C?
e\perinientallj determined constant = gas phase maw tran-fer coefficient = experimentallj determined comtant = liquid phaae inaqs transfer coefficient = experimentalh determined const ant gas compressibility correction factors per cent by \%eight liquid loading height equivalent to a theoretical plate partition coefficient an experimentally determined constant capacity ratio column length distance separating two peaks measured in qtandard deviations number of theoretical plates an empirically determined esponent column inlet pressure column outlet p r e-xw r e a n experimentally determined constant absolute temperature time
column eait velocity column free gas space volume of substrate in column column resistivity experimentally determined constant relative volatility
=
LITERATURE CITED
(1) Ayers, B. O., Loyd, R. J., IleFord, 1).D., AKAL.CHEY.33, 986 (1961). ( 2 ) DeFord, D. D., Loyd, R. J., Ayers, B. O., Ibid., 35, 427 (1963). (3) Giddings, J. C., Ibid., 34, 1186 (1962).
(4) Giddings, J. C., Seager, S. L., Stucki, L. R., Steward, G. H., I b i d . , 32, 867 (1960). ( 5 ) Hooke, K., Jeeves, T. A., J . .4ssoc. Computing Mach. 8, 212 (1961). (6) Mugele, R. h.,IBM Systems J . 1, 2 (1962). ( 7 ) Perrett, R. H., Purnell, J. H., ASAL. CHEM.35,430 (1963). (8) Purnell, J. H., J . Chem. SOC.1960, 1268. (9) Purnell, J. H.,,,Quinn, C. P., “Gas Chromatography, R. P. W. Scott, ed., p. 184, Butterworth’s, London, 1960. RECEIVEDfor review April 30, 1964. Accepted July 23, 1964. 15th Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 2-6, 1964.
Critical Evaluation of a Platinum-Bath, Vacuum-Fusion Procedure for the Determination of Oxygen and Nitrogen in Steels VELMER A. FASSEL, F. MONTE EVENS, and C. CLIFTON HILL lnstitute for Atomic Research and Department o f Chemistry, lowa State University, Ames, lowa
b Although analytical results for oxygen in steels obtained b y the ironbath, vacuum-fusion method are generally accepted as being reliable, the validity o f the nitrogen results has been repeatedly questioned. A critical comparison o f the nitrogen results obtained b y a modified platinum-bath, vacuumfusion procedure and b y the Kjeldahl, isotope-dilution, caustic-fusion, and arcextraction techniques has shown that quantitative accuracy can b e achieved under the platinum-bath environmental conditions described in this paper. The oxygen and nitrogen content o f 20 to 30 half-gram samples can b e determined in a single crucible without loss of accuracy and precision. The average analysis time per sample is 20 minutes.
T
HI,; I~I:TERMISATIOS of osygen and nitrogen in steels by the iron-bath, vacuum-fusion method (18, 19) has k e n ciisrus.sed in many published
papers. In these papers the view has been generally expressed t,hat, under optimal experimental conditions, reliable analytical results can be obtained for osygen in most, if not all, steel compositions. The situation with respect to nitrogen has not been as encouraging. The validity of the nitrogen results has through the years been clouded by the repeated insinuation that the nitrogen values so obtained are lower than those given by the Kjeldahl procedure. A cooperative analytical study was undertaken in 1949 by the British Iron and Steel Research -Issociation (I3ISR.L) to resolve these uncertainties. Their resiilts ( 5 ) gave sup1)ort to the view that the vacuum-fusion procedure provides reliable d a t a for both oxygen and nitrogen if the determinations are made under optimal experimental conditions. However, in an exact statistical sense, their conclusion that excellent agreement existed between the nitrogen resulta obtained by the Kjeldahl and
vacuum-fusion methods appears to have flattered the actual experimental situation. The analytical results which inay be strictly compared (Table X L I , reference 5 ) show that the Kjeldahl procedure gave higher results for 17 samples, agreed on 7 samples, and gave lower results than the vacuum-fusion method on only 7 samples. It is also worth noting that the analytical results on six out of the seven samples containing strong nitride-forming elements (AI, Si, Zr, Ti) %ere obscured with uncertainties. Either the Kjeldahl nitrogen values were considerably higher than the vacuum-fusion results, or acceptable d a t a could not be obtained by one of the methods. Substantial differences in the vacuum-fusion results on several qamples were attributed to segregation, although values obtained by the Kjeldahl procedure on the same samples showed acceptable agreement. More recent studies by Ihida ( I I ) , LIasson and Pearce (15), Karp, Lewis, and Melnick ( I $ ) , and Pearce (16) have VOL. 36, NO. 11, O C T O B E R 1964
21 15
Table I. Oxygen and Nitrogen Recovery as a Function of the Quantity of Iron Conditioning Metal Added to the Platinum Bath
Iron conditioner added Fein to bath bath Xitrogen (grams) (.ivt. %) (wt. %) 0 0 0 0090 0 00 0 30 0 8 0 0090 0 0093 0 96 2 7 7 3 0 0093 2 7 9 8 0 0094 7 0
Oxygen (wt. 70) 0 0004 0 0003 0 0080 0 0082 0 0084
provided rather conclusive support to the premise that the vacuum-fusion procedure often leads to low results for nitrogen. The basic cause of the lower nitrogen results does not appear to be a simple one. From experimental observations and thermodynamic considerations, Sloman et al. (19) and Ihida (11) have concluded that nitrogen evolution from molten steel results from the direct thermal dissociation of metal-nitrogen bonds in the melt. Kubaschewski’s (19) calculations on various nitride decomposition reaction mechanisms provide encouraging support that the usual operating temperatures (1800’ to 2000’ C.) should lead to rapid and quantitative dissociation of the nitride bonds in the melt. However, these calculations are subject to considerable error because of the lack of definitive data on the free energies of formation of nitrides, and on the eventual fate of the metal freed by the dissociation reactions. Moreover, these calculations shed little light on the solubility and extraction behavior of nitrogen in the melt. I t is known, for example, that the solubility of nitrogen in molten iron increases with temperature (21). Ihida (11) has concluded that in spite of the relatively high decomposition pressure of some nitrides, a comparatively large amount of nitrogen remains in the melt, even under a dynamic vacuum of 10-4 to 10-5 Torr. I n fact, Ihida ( 1 1 ) found that some of the residual nitrogen was expelled from the melt upon cooling. Moreover, he also showed that some of the “missing” nitrogen in the vacuumfusion determination was recoverable by subsequent analysis of the spent vacuum-fusion melt. The BISRX ( 5 ) study uncovered a considerable amount of experimental evidence that the last traces of nitrogen became progressively more and more difficult to extract, particularly in the presence of strong nitride-forming elements in the melt. Further substantiation of the inference that difficulties in quantitatively transferring nitrogen from the melt to the gas phase is the primary cause of the low results is found in hlasson and Pearce’s 21 16
ANALYTICAL CHEMISTRY
( 1 5 ) application of the isotope-dilution approach. Quantitative extraction of the nitrogen was not required in their technique, and it is significant that they achieved excellent agreement between the Kjeldahl and vacuum-fusion, isotopedilution results. A widely used variant of the 1 acuumfusion method employs a platinum bath for the extraction phase of the determination (3, 4, 9, 26). Since nitrogen is insoluble in platinum (65), this en\ ironnient should be more conducive to the quantitative transfer of the nitrogen into the gas phase. h l though other investigators (6, 24) have employed the platinum-bath environment for the determination of oxygen in steels, no definitive study on nitrogen has been made. We are aware, through personal communications, that variations of the platinum-bath technique have been employed by analysts in the steel industry. The only published account we have seen (22)came to our attention after our manuscript was submitted for publication. In that paper the authors reported quantitative recovery of nitrogen on five steel samples when a platinum bath was used. The experimental conditions employed by usi.e., a n extraction temperature of 1850’ C., the simultaneous addition of 0.5 gram of fresh platinum with each sample, and maintaining the platinumto-sample weight ratio above 4 to 1have not been previously employed. The results reported in this paper provide an extensive comparison of analytical results obtained by a modification of the platinum-bath, vacuum-fusion procedure with the values given by Kjeldahl, isotopedilution, caustic-fusion, arc-extraction, or iron-bath, vacuum-fusion procedures. These data provide adequate documentation that accurate results can be obtained for both oxygen and nitrogen, by the platinum-bath procedure described, for all steel compositions investigated. EXPERIMENTAL
Apparatus and Materials. Vacuumfusion gas analysis unit [ N R C Equipment Corp., Model 912s (14, SS)]. Graphite crucible and funnel (Ultra Carbon Products Co., C-625, F-703) packed in -200-mesh graphite powder (UCP-2). Guldner-Beach type furnace (IO), graphite parts assembled in quartz tube and suspended inside an air-cooled borosilicate glass shell. An ionization pressure gauge (National Research Corp., Type-507) was attached to the furnace section through a liquid nitrogen trap. Induction heating unit (Lepel High Frequency Corp., Model T-2.5B). Number 12-gauge platinum wire containing less than 0.001 wt. % oxygen and less than 0.0005 wt. 7cnitrogen, cut into 13-mm. segments.
Procedure. Solid samples were c u t into cubes of appropriate dimensions and surface-cleaned by d r y abrasion with a fine steel file. Samples in the form of metal chips were pressed into a single 6.4-mm. diameter cylinder with a briquetting press (;ipplied Research Laboratory, Model KO. 52) operated a t 8000 p.s.i. The chip samples were not cleaned prior to pressing into pellets. The operating conditions employed for analytical measurements were similar to those described by Wilkens and Fleischer (26). The crucible was outgassed a t 2400’ C. until the gas evolution rate was less than 0.1 micron liter per minute. Upon completion of a furnace and crucible outgassing period, the furnace temperature )\-as decreased to 1850’ C. and a minimum of 35 grams of platinum was added to the graphite crucible, melted, and degassed. Preliminary experiments revealed that rapid and quantitative extraction for most steel compositions could be consistently achieved for the first 3 or 4 samples. Quantitative extraction could be maintained by the simultaneous addition of 0.5 gram of platinum with each steel sample. The addition of platinum with each sample is considered an essential requirement for obtaining accurate nitrogen results. -4ppropriate blank corrections were made for the gases evolved from the platinum added with each sample. -4 phenomenon commonly observed with the platinum-fusion technique is the necessit,yof preconditioning the pure, degassed bath with an amount of the matrix metal prior to sample analyses in order to achieve quantitative extraction of oxygen. The data summarized in Table I show that this requirement applies to iron-base samples as well. Individually preconditioned baths were used for each sample run in this It is seen t,hat when experiment. the weight per cent iron was brought up to 2.7 by the addition of preconditioning iron, maximal extraction of oxygen was achieved from samples subsequently added to the bath. Interestingly, this preconditioning does not appear to be required for quantitative evolution of the nitrogen content. Since nitrogen evolution from the melt is believed to proceed through direct thermal dissociation of metal-nitrogen bonds, it is not necessary to provide carbon to the melt for this process. I n contrast, for the efficient carbon reduction of metal-oxygen bonds in the melt, a n adequate concentration of carbon in solution would seem to be an essential requirement. The solubility of carbon in pure platinum may not provide an adequate concentration for this purpose. Total gas extraction from 0.5- to 1-gram samples, as measured by the return of the furnance pressure to its original value, was completed in 15 to 30 minutes. RESULTS
Table I1 shows a typical comparison of the data obtained by the platinumbath procedure with correbponding
Table II. Comparisori of VacuumFusion Data for Iron-Bath and Platinum-Bath Proc'edures
Iron Iron batho batho 1650 2!150 Samplen C. C. Kitrogen NB88h 0 013 0.016 0 020 XBS 101d 0 018 0 0053 0 0053 NBS 461 S B S 462 0 0062 0 0078 Oxygen S B S 8h 0 036 0 031 KBS l 0 l d 0 027 0 020 0 025 0 025 KBS 461 S B S 462 0 0056 0 0048 Chemical composition shown 111. All values are in wt. VO.
Table 111.
Platinum bath, 1850 C. 0,016
0 024 0 0071 0 0092 0 0 0 0
038 027 028 0082
in Table
values obtained with the operating conditions described for a n iron-bath procedure a t 1650' C. (1, 5 , 15, 18, 19) and 2150' C. ( 1 6 ) . I t is evident from the values shown that the platinumbath technique yielded oxygen values equivalent to or greater than the ironbath procedure a t 1650" C. The lower oxygen values obtained a t 2150' C. suggests appreciable gas gettering by the metal vaporized during analysis (2, 17) at this elevated temperature. The data shown for nitrogen confirm the work of Masson and Pearce (15) since improved nitrogen recovery was obtained by increasing the iron bath temperature to 2150' C. However, the significantly greater nitrogen values obtained for three of the samples by the platinum-bath procedure indicate incomplete recovery of nitrogen during
Comparative Nitrogen and Oxygen Data for Various Steel Samples
Sample 1. 8h (NBS)
Description Bessemer steel (chips) 0 . 5Yc Mn
2.
B. 0. H. (chips) 0.87, Mn, 0 . 2 7 , Si
152 (NBS)
3. l l l b (NBS) 4.
122c ( S B S )
5.
lOld (NBS)
6.
10le (NBS)
SAE (4620)(chips) 1.8% Ki, 0.37, Mo 0.77, h h , 0.37, Si Cast iron (chips) 0.670 Mn, 0.67c Si High alloy (chips) 18y0 Cr, 9% Ni 0 . 5YGSi, 0 . 7Yc ,Mn High alloy (chips) 1870 Cr, 9% Xi
Concentration (wt. %) Pl'itrogen Oxygen 0.016 0.038 0.017 0.016 0.016 0.032 0.0036 0.004 0,0033 0.0048 0.0051 0.0045 0.0053 0,005 0 024 0 024 0 024 0 041 0 039 I
7. 125a (NBS)
Silicon Steel (chips) 3.37, Si
0 0039 0 0046 0 0050
8. 343 (XBS)
High alloy (chips) 16% Cr, 2Y0 Ni
0 068 0 067 0 074
9. 129a(NBS)
SAE X1112 (chips) O . S ~ A, h , 0 . 3'3, S 18% Cr, 7yc Ni, 294 A h , 1% Nb 167, Cr, lyOMn, 1% Si
0.013 0.014 0,084 0.083 0.032
10. Type 347
11. Type430
13. 1042 (KBS)
Low carbon, 0 . 37', Mnf
Bessemer 0 , 7 y 0 Mnf
0.031 0.035 0.030 0.056 0 027 0 020
0 019 0 028
0 028 0 020 0 019 0 069 In/
17. E
Low alloy
18. USS 2
Silicon steel, 3.257, Si
19. US5 3
20. 1296-1
21. BPL-1
22. Type 436
Silicon steel, 3.25% Si
Silicon steel, 3 . 3 7 , Si
Silicon steel, 3.37, Si
17% Cr, 1% Rlo 0 .5 7 , K b Ta
+
Concentration (wt. 7c) Nitrogen Oxygen 0.0036 0.0052 0.005 0.002
0,005
0.0031 0.0017 0.0025 0.0065 0.007
0,0045 0.0043 0,0040 0,004
0,0073 0,007 0.014 0.017
0.0041 0.0043 0.0039 0.0052 0.0045 0.0047 0,005 0.0045 0.0029 0.0092 0.0089 0,010 0.0102 0.0060 0.007.6 0.0081 0.0080 0.0077
0.018 0.0048
0.004 0.0033 0.0045 0,0050
0.004 0.011 0.0108 0.0107 0,0099 0.0085 0.044 0.044 0,045
Ibid,’,’ 31. 1722 i l S T , Y l . (3) Bennett, 8. J . ) Covington, L. C., Ibid., 30, 363 (1958). (4) Booth, E., Bryant, F. J., Parker, il., Analyst 82, .iO (1957). ( 5 ) British Iron and Steel Research Association, “Iktermination of Sitrogen in Steel,” Special Rept. 62, Iron and Steel Institute, London, 1958. (6) Covington, L. C., Bennett, S. J., ANAL.CHEM. 3 2 , 1334 (1960). ( i j Evens, F. l l . , Fassel, Y. A , , Ibid., 35. 1444 (1963). (8) &kcen, S . A , , T r a n s . J l e t . Soc. AIME. 212, 93 (19S8). ( 9 ) Gregory, J. S . , Mapper, D., d n a l y s t 80,230 (1955). (10) Guldner, \V. G., Beach, A. I,., AKAL. CHEM.22. 366 il950). ( 1 1) Ihida, ’ AI., J&dn Analgst 8, 786 (1959). (12) Karp, H. S., Lewis, L. I,., 3lelnick, 1,. AI., J . Iron Steel Inst. 200, 1032 (1962). ( 1 3 ) Lewis, L. L., Slelnick, L. SI.,ANAL. CHEM.34,868 (1962). (14) lkAIahon, W. J., Foster, I,. S., J . C‘hem. Edzrc. 30, 609 (1963). (15) 1Iasson, C. It., Pearce, AI. L., Trans. X e t . SOC.AIME. 224, 1134 (1862). (16) Pearce, 11. L., Ibid., AIME. 227, 1393 (1063). (17) Sawa, S., Tetsu to Hegane 38, 567, 672 (1952). ~
VOL. 36, NO. 1 1 , OCTOBER 1 9 6 4
21 19
(18) Sloman, H. A4.,J . Znst. Metals 71, 391 (1945). ~ c, ~A., (19) sioman, H. A., H (appendix by H. Kubaschewski) J . Znst. Metals 80, 391 (1951). (2”) H. Ponder Metallurgy,” Special Rept. ‘yo. 5 8 , Iron and Steel Institute, London, pp. 44-9, 1956. ( 2 1 ) Smithells, C. J., “Metals Reference Book” Vol. 11, 3rd ed., pp. 576-7, Butterworths, Washington, 1962. S1omanj
(22) Sorniya, T., Hirano, S., Kamada, H., Ogahara, I., Talanta 11, 581 (1964). ~(23) Staley, ~ ~H. G., , Svec, H. J., Anal. Chim. Acta 21, 289 (1959). (24) Still, J. E., “Determination of Gases in Lletals,” Special Rept. S o . 6 8 , Iron and Steel Institute, London, pp. 43-63,
(26) Wilkens, D. H., Fleischer, J. F., Anal. Chim. Acta 15, 334 (1956). (27) \Tinge, R., Fassel, V. A . , Pittsburgh Conf. on Anal. Chem. and Applied Spectroscopy, 1964. (28) Yeaton, R. A.,Vacuum 2, 151 (1952).
(25) Turovsteva, z, hi., ~ ~ L, L,, ~ “Analysis of Gases in Metals,” Academy of Sciences USSR. Authorized Translation from the Russian, Consultants Bureau, p. 39, 1959.
i ~ , RECEIVEDfor review March 23, 1964. iiccepted July 16, 1964. Work performed in Ames Laboratory of G . S. Atomic Energy Commission.
1 a&? I U V Y .
S pect ro p hoto met ric Determinutio n of Unsymmetrica I Dimet hyI hyd razine Employi ng Chromo tro p ic Acid NORMA V. SUTTON Research Department, Rockefdyne, A Division of North American Aviation, Inc., Canoga Park, Calif. 91 304
b The spectrophotometric determination of unsymmetrical dimethylhydrazine (UDMH) in aqueous solution in the part per million range is important because of the widespread use of UDMH as a liquid propellant. The hydrazines are somewhat toxic substances and possess distinctive physiological characteristics. This is an empirical analysis based on the oxidation of UDMH to the relatively stable formaldehyde. The reaction of this product with chromotropic acid gives a purple color whose absorbance conforms to Beer’s law in the range 1 to 3 p.p.m.
methyltetrazene. Whether the tetramethyltetrazene is a n intermediate in the oxidation of I - D M H to formaldehyde has not been ascertained, but it has been empirically established that a n aqueous solution of unsymmetrical dimethylhydrazine can be refluxed overnight in the presence of atmospheric oxygen and that a stable oxidation product, formaldehyde, can be quantitatively determined wing chromotropic acid (3, 8). This paper describes a new, simple, and selective procedure for the analysis of aqueous U D l I H solutions. EXPERIMENTAL
T
THE CNSYMMETRICAL disubstituted hydrazines could be oxidized to the corresponding substituted tetrazenes was reported by Audrieth and Ogg. Later papers by Carpino ( 2 ) and by Overberger, Lombardino, and Hiskey ( 6 ) noted that the tetrazene formation was the normal product of the oxidation of the 1,ldisubstituted hydrazines. Experiments were undertaken in this laboratory to obtain the tetramethyltetrazene which might be utilized to form some stable, easily identifiable product. Upon reaction of 0.02M U D k I H with concentrated H2S04,mass spectrometric examination of the gases evolved indicated, among other compounds, diazomethane. \Then oxidizing 0.002M UDMH with 0.1V calcium hypochlorite, a fleeting red color to the solution and the odor of escaping formaldehyde were observed. Mcl3ride and Kruse (4) had mentioned a similar transitory color phenomenon when working with the disubstituted hydrazines and had attributed it to the species (CHJ2?;+ = h;-, This species, in neutral or basic solution, dimerized to form the tetra-
HAT
2 120
ANALYTICAL CHEMISTRY
Apparatus a n d Reagents. Spectrophotomet’ric measurements were made with a Beckman DK-2 ratio recording spectrophotometer using 1-cm. silica cell?. All chemicals used were 1Iallinckrodt .$nalytical Reagent, grade, unless otherwise indicated. The T=D;\IH was obt,ained from the Westvaco Chlor-,\lkali Division of Food Machinery and Chemical Corp. Analysis by iodate titration (9) indicated a concentration of 99.47,. The chromot,ropic acid (43dihydroxy - 2 , i - naphthalene - disulfonic acid), practical grade, was obtained from Matheson Coleman & Bell. Procedure. PREPARATIONOF STANDARD CURVE. Assay t h e formaldehyde (37’33 solution ( 7 ) . n’eigh accurately about 3 grams of this solution and dilut,e to exactly 1 liter. Take suitable aliquot,s and again dilute to volume so that the resultant dilution will be 20 to 40 p p m . HCHO. To accurately measured amounts (0.25 to 1.50 nil.) of the HCHO standard in a 50-ml. Sessler tube add 10 to 70 mg. of solid chromotropic acid, followed, cautiously, by concentrated sulfuric acid to a total volume of 50 nil. Heat in a water bath a t 60” to 70” C. for 10
minutes. Plot the absorbance a t 580 nip 21s. the resultant concentrat,ion. DETERMINATION OF CDMH. Heat 200 ml. of the sample containing approximately 50 1i.p.m. UDRIH in a 500-ml. boiling flask under a capped, long (20 to 25 inches) reflux condenser for 20 hours a t a temperat,ure of 90” C. (,Z water-cooled cold finger-type apparatus may be used with equal success if it is so constructed that it, rests on the neck of a 1000-ml. wide-mouthed Erlenmeyer which contains the same amount of sample and is heated under the same conditions.) Cool and rinse the walls of the container with a small amount of the refluxed sample, then syir.1 the solution to ensure adequate mixing. Using 1 to 3 ml. of this thoroughly mixed sample, proceed as with the HCHO determination. The resultant reading, as HCHO in p.p.m., is mnltiplied by two to obtain p.1i.m. U D l I H . The reaction is mole for mole, since the molecular weight of I‘DAIH (60.10) is twice that of formaldehyde (30.03). ~ I I E X T I F I C A T I O XO F OXIDATIOS P R O D UCT. The spot test identification of formaldehyde was confirmed by its reaction with casein ( 5 ) . The spectrophotometric scan of the refluxed L7DMH-chromotropic reaction product was identical with that of the formaldehyde-chromotropic reaction product with maximum absorbance a t 580 nip. ACCCRACY ASD PRECISION. Separate determinations were made on 350 water samples containing 1 to 50 p.1i.m. L-DlIH. Xliquots of these solutions were prepared, and within the concentration of 40 to 150 p g . of r D l I H in 50 nil. of chromotropic reagent solution (1 to 3 p.1i.m.). the method showed a variance of 0.01, a standard deviation of 0.10. The mean error was 0.03 and the relative error was 1.57c. INTERFERENCES. This method was primarily concerned with the examination of V’DlIH in natural water sb-stems. ;inaIyses of these s a m i k q revealed as much as 500 1i.p.m. chloride, 250 p.13.m.
