ACKNOWLEDGMENT
The statistical evaluation of data was done by R.L. Hafley of the Matheniatics Dellart ment, Westinghouse Research Laboratories. LITERATURE CITED
( 1 ) Codell, ll., “hna.:Iytical Chemistr; (Jf Titaniurn Metals :and Compounds,
Chap. 21, Interscience, Yew York, 1959. (2) Easterday, C., U.S. Industrial Chemicals Co., Ashtabula, Ohio, private
communication^ 1963.
(3) Kriege, 0. H., Rudolph, J. S., Talanta 10. 21.5 ~ - 1196.11 7
\ - - - - I
(4)Walter, E. R., Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1956. ( 5 ) Yao, T. C., Harrison, R. E., Second
National Meeting, Society for Applied Spectroscopy, San Diego, Calif., October 1963. (6) Yao, T. C . , Porsche, F. W., ANAL. CHEM.31, 2010 (1959). RECEIVEDfor review February 5, 1964. Accepted May 12, 1964. 2nd National Meeting of the Society for Applied Spectroscopy, San Diego, Calif., October 1963.
Approximate Degrees of Polymerization of Cellulose Esters from Intrinsic Viscosities LEO B. GENUNG Cellulose Technology Division, Eastman Kodak Co., Rochester, N. Y.
b Conversion of intrinsic viscosities to approximate degrees of polymerization (DP) is sometimes useful for obtaining a measure of molecular size of cellulose esters. Equations and graphs are presented for this purpose using cellulose viscosities in cupriethylenediamine and cuprammonium solution and cellulose ester viscosities in acetone, methylene chloride-alcohol, acetic acid, and pyridine. Equations are also given for c:onversion of inherent to intrinsic viscosities and for applying a correction for degree of substitution when needed. The equations and the calculated DP values necessarily vary considerably, depending on all the factors involved in each case. The various equations for a given conversion, such as intrinsic viscosity of a cellulose ester in acetone to DP, can b e compared quickly by inspection of graphs of the equations. DP data were calclulated applying these equations to viscosities of three cellulose acetates and two acetate butyrates. The results are shown so comparisons can b e made for a variety of circumstances.
D
(DP) and molecular weight (MW) data have more physical significance in characterizing cellulose esters than viscosity data expressed as seconds, centipoises, relative viscosities, or intrinsic viscosities, although the latter are practical and useful. I t is desirable to be able to make even approximate conversions of viscosities to D P . Battista ( 4 ) , for example, described routine calculation of “basic degree of polymerization” from the viscosity in cuprammonium solution of cellulose, or of cellulose regenerated from cellulose acetate, using Kraemer’s relationshrp (12), D P = 260 X qaP:c, where c is the concentration in grams per 100 ml. (of solution and is 0.50 or less. EGREE O F POLYMERIZATION
The literature now describes careful fractionations of cellulose esters followed by measurements of intrinsic viscosities, [ q ] , and usually number average molecular weights, .If,,, by osmotic pressure. The data are plotted on log-log paper and correlating equations determined of the form:
which was proposed by Mark (14) and by Houwink ( I I ) . DP may be used instead of .\f, where -11 = D P X unit molecular weight. The exponent 01 is a n index of the extent of molecular coiling in solution; the higher the value of 0 1 , the more extended is the molecule. Graphs of these equations on log-log paper show the relationship between intrinsic viscosity and degree of polymerization. Equations in the form of Equation 1 have been solved for D P :
DP
K’[17]1’a
(2) so DP can be calculated readily from observed intrinsic viscosities. Several of these equations are compared by plotting them together. The equations have been compared further using viscosit,y data already available in this laboratory. When making conversions of intrinsic viscosity to D P , the results must be regarded as first approximations only. I t is assumed that the relationship reported in the literature applies to the particular sample being tested, but differences in polymolecularities of the individual samples and the reference samples can introduce errors difficult to evaluate. Meyerhoff (16) has discussed thoroughly the viscometric determination of molecular weights of polymers. Intrinsic viscosity is proportional to a viscosity average D P or A N 7 > but corthe relation is often made with .TI, number average molecular weight. Michie (17) presented equations for cellulose in cuprammonium solution =
which indicate that for a given intrinsic viscosity, weight average DP is about 15% greater and viscosity average DP about 50% greater than number average D P . Other possible variations include differences in solubilities of the various esters in the viscosity solvent, in technique of viscosity measurement, and in degrees of substitution of these esters. If i t is assumed that the intrinsic viscosity of an ester is proportional to its cellulose content, a correction can be applied for this latter variable. Some of the difficulties introduced by varying degrees of substitution and borderline solubility of the esters in organic solvents can be avoided by measurements of the cellulose viscosity in cupriethylenediamine (cuene), cuprammonium (cuam), or similar solutions. Some cellulose esters will deesterify and dissolve directly in cuam or cuene solution. In these cases the sample weight is adjusted to give the desired amount of cellulose in the solution. Insoluble esters must first be saponified and the regenerated cellulose isolated without degradation Cuam solution will dissolve almost all cellulose acetates and acetate propionates and acetate butyrates containing up to about 14% of the higher acyl, depending somewhat on the physical condition of the sample. Cuene is a less powerful solvent and will not dissolve cellulose acetates of high acetyl content or most of the mixed esters. I n spite of these uncertainties, comparative data which can be calculated or read from a graph are just as useful as intrinsic, relative, or absolute viscosities and have a t least a semblance of structural significance DEFINITIONS AND EQUATIONS
Inherent Viscosity = ( 1 7 I c =
2*303loglo “ = 9.21 log 7 7 C
where c
=
(3)
concentration in grams per
VOL. 3 6 , NO. 9, AUGUST 1 9 6 4
1817
100 ml. ity
=
0.25 and vr
=
relative viscos-
Intrinsic Viscosity = [’I]
[v] = lim 2.303 log vF = c-0
where
c
lim
vep
-
1771
viscosity
=
vr -
1 Baker-Philippoff Equation is a very
convenient means (8) for calculation of intrinsic viscosity from a single relative viscosity measurement:
= 4a
0.1086{7]a.*a)I [(antilog a
c
O‘C
vSp= specific
(4)
Intrinsic Viscosity from Inherent Viscosity. Substitution of Equation 3 in Equation 5 a t c = 0 . 2 5 gives:
-
]
Table 111. Comparison of Intrinsic Viscosities in Methylene Chloride-Ethanol and in Methylene Chloride-Methanol
(6)
Thus when the Baker-Philippoff constant a is known for the solute-solvent system, inherent viscosity can be converted readily to intrinsic viscosity.
Cellulose acetate, yo acetyl 44.8 44.8 43.3 43.4 40.4 32.6
EQUATIONS FOR CELLULOSE A N D CELLULOSE ESTERS
where a is a constant characteristic of the solute-solvent system. Some values for a found in this laboratory are: 3 for cellulose in cuene or cuam solution, 9 for cellulose in iron-sodium tartrate, 3 for cellulose acetate in methylene chloride-methanol (90: 10 by weight), 10 for cellulose acetates and some mixed esters in acetone, 3 for high butyryl cellulose acetate butyrates in acetone, 4 for cellulose acetate butyrate in pyridine, and 4 for cellulose acetate in acetic acid.
Table I.
Several equations from the literature are presented for calculation of M W or D P from intrinsic viscosities (or from inherent viscosities) measured in several different solvents. Expressions in terms of MW have first been converted to D P using the unit molecular weight calculated from the known acyl content of the ester. The resulting equation was solved for D P . (The exponent is then the reciprocal of a.) Equations in terms of inherent viscosities have been adjusted to intrinsic viscosities using Equation 6. Table I presents the equations
DP from Intrinsic Viscosities of Cellulose
Basiso
Author (reference) Cellulose in cuene Gloor and Klug (9) Newman, Loeb, and Conrad (19) Alexander, Goldschmid, and Mitchell ( 1 )
190 170 114
1 1 1.24
SD O P b Ref. 2 and 20
Cellulose in cuam 260 1 UC Kraemer (12 ) 200 1 Gloor and Klug (9) 188 1.52 c Cumberbirch and Harland ( 7 ) 223 1 LS and UC Marx-Figini and Schulz (16) a SD = sedimentation and diffusion; OP = osmotic pressure; UC = ultracentrifuge; LS = light scattering. References 2, 19, and 20. c From [4] = 0.0319 (DP)O.Q7 based on viscosities of celluloses regenerated from cellulose acetates of known IIP. Table 11.
DP from Intrinsic Viscosities of Cellulose Esters
2.27 1.60 2.14 2.12 1.43 1.15
2.33 1.58 2.12 2.07 1.38 1.10
thus found for cuene and cuam viscosities, and Table 11, those found for cellulose esters in acetone, methylene chloride-alcohol, pyridine, and acetic acid. Table I11 shows that viscosities of cellulose acetates are practically the same in methylene chloride-ethanol, 80:20 by volume, and in methylene chloride-methanol, 90: 10 by weight, over a wide range of acetyl content. This permits application of the Cumberbirch and Harland ( 7 ) equation to data obtained using the latter mixture. Table I1 includes, for use in Equation 7 , the cellulose content of the ester used by each author. Equations of the type D P = K ’ [ v ] ~ ’ ~ give a straight line for D P us. [77] only when the exponent is one. A linear plot for any value of 1/ 01 may be obtained using log D P us. log [77]. Figure 1 shows such plots for the various equations for cellulose esters in acetone. For a given value of 1 ’ a , parallel lines are obtained but laterally displaced depending on the value of K’. For a given value of K’, lines of decreasing slope are obtained as l / a increases. Examination of Figure 1 shows the areas of agreement and disagreement among the various equations. Similar graphs may be constructed easily by substitution a t two points on log-log paper for each equation. When suitable scales are chosen these serve as working graphs to determine D P from [VI.
Author (reference) Acetone Kraemer (12) Sookne and Harris ( 2 1 ) Tamblyn, Morey, and Wagner (22) Phillip and Bjork (20) Cumberbirch and Harland ( 6 ) Moore and Tidswell (18) Methylene chloride-alcohold Cumberbirch and Harland ( 7 )
? 61.4 50,4 60.9 61.5 61.5
230 150 140 120 132 137
1 1 1.20b 1,llC 1.32 1.28
CC OP OP OP OP OP
56.4
147
1 20
Ref. 6 and 7
Pyridine OP Tamblyn, Morey, and Wagner (22) 50 4 155 1 136 Moore and Tidswell (18) 61.5 166 1 59 OP Acetic acid 50.4 1 , 13e OP Tamblyn, Morey, and Wagner ( 8 2 ) Moore and Tidswell ( 18) 61.5 103 13’ 1.39 OP a UC = ultracentrifuge; OP = osmotic pressure. Calculated using unit M W of 315. 263 unit MW. Either methylene chloride-ethanol 80:20 by volume or methylCalculated using 315 unit MW and Bakerene chloride-methanol 90: 10 by weight. Philippoff constant a = 4. ~
181 8 *
Observed intrinsic viscosity Methylene Methylene chloride chloride ethanol methanol 80:20 vol. 90: 10 wt.
ANALYTICAL CHEMISTRY
ADJUSTMENT FOR DIFFERENCES I N DEGREES OF SUBSTITUTION
Each of the intrinsic viscosity-DP equations presented is based on measurements of a cellulose ester of stated acyl content. As pointed out by Harland (IO), “The intrinsic viscosity is dependent on the degree of substitution of derivatives. I t is essential, therefore, to ensure that the intrinsic viscosity of a particular sample is not used to calculate a DP from a relation based on a different degree of substitution.” If n e assume, however, that the intrinsic viscosity of a cellulose ester depends primarily on its cellulose content, a correction can then be made for differ-
I ALEXANDER.GOLDSCHMID,hMlTCHEL~
REGENERATED CELLULOSE
2 NEWMAN, LOEB,ACONRAD
5
CUAM 3t-
CELLULOSE ACETATE IN METHYLENE CHLORIDE METHANOL 90 IO w t
3 GLOOR L KLUG 4 CUMBERBIRCH h HARLAND 5 MARK-FIGIN1 h SCHULZ 6 KRAEMER
6 4
7 TAMBLYN,MOREY, L WAGNER O I MOORE L TIDSWELL
4!
7 10
20
,40
60
80 100
I
I
200
400
I
IO
1
600 800
Approwmate degree of polymerization
Figure 1. Conversion of intrinsic viscosities of cellulose esters in acetone to upproximate degrees of polymerization
ences in composition between test samples and the ester used for calibration. The cellulose content is 100% minus per cent acyl in the ester as found b y analysis. Such a correction may be made easily as follows : adjusted [v] = observed [v] X cellulose content of calibration ester cellulose content of test sample
(7) The adjusted intrinsic viscosity may then be substituted in one of the equations or the corresponding D P read from a graph. The effectiveness of Equation 7 for adjusting intrinsic viscosities for differences in cellulose contents is shown by data in Table IS'. A cellulose propionate series (51.7 to 46.7'% propionyl) was used because all members of the series had been found to give regenerated
Table IV.
Cellulose, yo 48.3 51.1 51.5 52.4 53.3
Effect of Correction for Cellulose Content" Intrinsic viscosity in acetone Corrected to Approx. av. DP Uncorrected 6 1 . 4 yo cellulose Uncorrected Corrected ~
2.31 2.41 2.42 2.47 2.55
347 362 363 370 383
2.94 2.90 2.89 2.90 2.94
441 Cellulose propionate series of varying propionyl and cellulose contents but the same cellulose viscosity.
viscosities and DP's show a predicted upward drift with cellulose content. The corrected values are in good agreement with each other, and the DP's (434 to 441) are about the same as those based on cellulose viscosities using midrange equations (Figure 6). The in-
cellulose of the same viscosity and hence the same DP. Intrinsic viscosities of the esters measured on acetone solutions were corrected to 61.4% cellulose basis by Equation 7, and DP's calculated for both sets of data using the Sookne and Harris equation (21). The uncorrected
I ALEXANDER,GOLDSCHHID,1MITCHEL~ 2 NEWMAN,LOEB,bCONRAD 3 GLOOR L KLUG
1
CUAW
I ALEKANDER.GOLDSCHYID,LMITCHEL~ 2 NEWMAN, LOEB,L CONRAD
3;
CELLULOSE ACETATE IN ACETONE
,5
4 CUMBERBIRCH A HARLANO 5 MARK- FlGlNl h SCHULZ 6 KRAEMER ~6
6
4 u
3 GLOOR L KLUG CUAM
4 CUMBERBIRCH h HARLAND 5 MARK-FICIN1 L SCHULZ 6 KRAEMER
CELLULOSE ACETATE IN
METHYLENE CHLORIDE METHANOL 90 I O w t PYRIDINE
METHYLENE CHLORIDE METHANOL 90 O I wt PYRIDINE
-
7
I TAMBLYN,MOREY, L WAGNER
IO
~~~
a
REGENERATED CELLULOSE IN CUENE
REGENERATED CELLULOSE IN CUENE
44 1 435 434 435
IO MOORE 6 TIDSWELL
ACETIC ACID
7 TAMBLYN,MOREY, k WAGNER 8 PHILLIP 6 BJDRK 9 SOOKNE A HARRIS IO MOORE k TIDSWELL
I
4 I
I
1
O I H
1 IO
Median 75 ICiO
Figure 3.
150
200
250
Approximate overage DP DP data on 32.670acetyl cellulose acetate
Based on [77] = 1.04 in cuene, 0.85 in cuam, 0.75 in methylene chloridemethanol, 1.02 in pyridine, and 67.470 cellulose content
Based on [7] = 1.49 in cuene 1.1 3 in cuam, 1.67 in acetone, 1.49 in methylene chloride-methanol, 1.49 in pyridine, 1.85 in acetic acid, and 60.570 cellulose content
VOL 36, NO. 9, AUGUST 1964
1819
: :4;
REGENERATED IN CUENECELLULOSE
3.
CUAM
$1
,2l ~NEWMAN, ~ ~ ~ ~ ~ LOEB,LCONRAD ~~,GOLDSCHMlD,6MlTCHEL~ 4 CUMBERBIRCH 6 HARLAND
'250
I 7
I
"
ACETIC ACID
Median 200
I
1
I
300
350
400
DP data on 17% butyryl cellulose acetate
Based on [v] = 1.73 in cuene, 1.38 in cuam, 1.69 in acetone, 1.40 in methylene chloride-methanol, 1.55 in pyridine, and 1.77 in acetic acid. Acetyl 29.3%, butyryl 17.170,cellulose 53.6%
trinsic viscosities in cuene, 2.55, and in cuam, 2.04, indicate that the D P is probably in the order of 430 to 460 based on the equations of Xewman, Loeb, and Conrad (19) and of Marx-Figini and Schulz (15 ) . DP DATA COMPARISONS
D P values calculated using the above listed equations with intrinsic or inherent viscosity data available in this laboratory on a variety of cellulose esters are shown in Figures 2 to 6. The cuene and cuam viscosities were determined on samples of cellulose regenerated from the esters by sodium methylate (13) or by saponification in dimethyl sulfoxide solution (3) with a nitrogen atmosphere in the flasks during saponification. These viscosities were measured on 0.1-gram samples a t 25' C. in 100 ml. of following solvents: purchased l . O M cupriethylenediamine solution (General Chemical Co. No. 1659) which was diluted to 0.5M during preparation of the solution; or cuprammonium hydroxide solution containing 3.00 f 0.05 gram of copper, 16.50 f 0.10 gram of ammonia, and 1.0 f 0.05 gram of sucrose per 100 ml. Relative viscosities were measured in a Wagner and Russell capillary viscometer (,E?), an instrument designed to minimize viscometry errors. Relative viscosities were calculated to intrinsic viscosities by the Baker-Philippoff equation using the constant a = 3. (Results by this procedure agree well with those by -4STM Standard Method D-1795-62.) Inherent viscosities of the cellulose esters were measured a t 25' C. with the same apparatus using 0.25-gram samples per 100 ml. of solution. The acetone ANALYTICAL CHEMISTRY
250
300
350
400
,
I
I
450
500
550
E
Approximate overage DP
Approximate average DP
1820
7 TAWBLYN,MOREY, 6 WAGNER 8 PHILLIP 6 BJORK 9 SOOKNE 6 HARRIS IO MOORE 6 TIOSWELL
4
PYRIOINE
lo Median
I
Figure 5. butyrate
IO
8 METHYLENE CHLORIDE METHANOL 90 O I wt.
7 TAMBLYN, MOREY, 6 WAGNER 8 PHlLLiP 6 BJORK 9 SOOKNE 6 HARRIS IO MOORE 6 TIDSWELL OI,
PYRIDINE
ZOO
4 CUMBERBIRCH h HARLAN0 5 M A R K - FlGlNl 6 SCHULZ 4$KRAEMFR 7-6
CELLULOSE ACETATE BUTYRATE IN ACETONE
5 MARK-FiGINI 6 SCHULZ
1
ACETIC ACID
I ALEXANDER.GOLDSCHYIO,LMIICHELL
2 NEWMAN, LOEB,& CONRAD 3 GLOOR 6 KLUG
3 GLOOR 6 KLUG
CELLULOSE ACETATE BUTYRATE IN ACETONE METHYLENE CHLORIDE METHANOL 9O:lO wt.
REGENERATED CELLULOSE IN CUENE
Figure 6. butyrate
DP data on 36.5%
butyryl cellulose acetate
Based on [v] = 1.79 in cuene, 1.45 in cuam, 2.00 in acetone, 1.58 in methylene chloride-methanol, 1.89 in pyridine, and 1.97 in acetic acid. Acetyl 1 3.1 %, butyryl 36.5%, cellulose 50.4%
used contained 0.4 f 0.0597, water. The methylene chloride-methanol mixture was 90:lO by weight. Pyridine was the commercial 2' grade redistilled to reduce its water content to 0.1 to 0.2%. The acetic acid has a purity of 99.8 to 99.9% as indicated by congealing point. Measured relative viscosities originally calculated to inherent viscosities by Equation 2 were converted to intrinsic viscosities by Equation 6 using the following Baker-Philippoff constants: acetone, 10 for cellulose acetates and the 17%-butyryl acetate butyrate, 3 for the 36.5%-butyryl acetate butyrate; methylene chloride-methanol, 3 ; pyridine, 4 ; and acetic acid, 4 (8). The intrinsic viscosities of the esters were adjusted by Equation 7 to compensate for the differences in acyl contents using cellulose contents shown in the figure captions and in Table 11. Viscosities of regenerated cellulose did not need to be adjusted because they are on a comparable basis already. D P data were then calculated by the indicated equation or read from one of the graphs. I n Figures 2 to 6 the D P data found for viscosities in each of the solvents used are plotted on scale for easy comparison. A median line is shown on each figure. (Equal numbers of values will be found above and below these lines.)
large ranges and many variations, as is to be expected. The highest values are given by the Moore and Tidswell (28) equation for pyridine solutions, closely followed by the Kraemer (12) equations for acetone and cuam. The lowest values are given by the Alexander, Goldschmid, and Mitchell cuene equation (1). Others which give D P values on the low side are the Cumberbirch and Harland ( 7 ) methylene chloride-alcohol equation and the Tamblyn, Morey, and Wagner equations (22). Median values tend to cluster around the cuam values calculated by the equations of MarxFigini and Schulz (15) and of Cumberbirch and Harland ( 7 ) . Differences in D P introduced by adjustments for differences in degrees of substitution may be considerable. If these equations are to be applied to a variety of cellulose esters differing in cellulose contents from the equation bases, this simple correction should be included in the calculations. It is possible, from the information presented, to select an equation for calculation of comparable D P data for practical purposes with full awareness of the magnitude of uncertainty involved. It is also possible, when even a single intrinsic viscosity is known for a sample, to estimate quickly the approximate degree of polymerization.
DISCUSSION
The various equations for a single viscosity solvent can be compared quickly by inspection of Tables I and I1 and graphs like Figure 1. I n some cases the lines cross, so an equation which gives a lower value a t low D P will give a higher value a t high D P . The D P data in Figures 2 to 6 show
ACKNOWLEDGMENT
All the viscosity data cited were taken from compilations made by my associates. LITERATURE CITED
(1) Alexander, W. J., Goldschmid, O., Mitchell, R. L., l n d . Eng. Chem. 49, 1303-6 (1957).
W. J., Mitchell, R. L., ANAL.CHEM.21, 1407 (1949). (3)8-12), but are limited to small samples and substantial amounts of fluoride. Sweetser (14) applied the Wickbold Oxyhydrogen flame combustion method, obtaining complete decomposition of trifluoromethane and tetrafluoromethane. ‘The technique was designed for sample: in the range of microanalysis and potentially was somewhat hazardous. Bailey and Gehring ( 1 ) applied the o\ygen bomb combustion technique to samples of u p to a few grams in the determination of traces of sulfur, fluorine] and boron in organic matwials. Eartkienicz and Robinson ( 2 ) applied the osyhldrogen flame techEVERAL
nique to the trace determination of fluoride, but were forced to rely on a less sensitive titrimetric method when metal irnpurit>iesproduced serious interference with the spectrophotometric method. By a unique combination of a modified oxyhydrogen flame-quartz combustion tube method of Hoggan and Battles ( 7 ) and a spectrophotometric measurement (5, 1 5 ) , fluoride can be determined simply and rapidly a t the low part per million level in organic materials. The procedure can accommodate samples of all sizes with comparable ease. The sample (gas, liquid, or solid in solution) is burned in an oxyhydrogen flame and passed over quartz packing at 1000° C., and the decomposition products are absorbed in boric acid solution. The resultant fluoride is determined spectrophotometrically with zirconiumSPADSS reagent. Triplicate analyses a t the I-p.11.m. level on a given sample can be made in less than 1 hour. EXPERIMENTAL
Apparatus. T h e quartz combustion apparatus is similar to t h a t of Hoggan and Battles ( 7 ) , except that the combustion gas bypass valve is removed, an improved gas control system is used, and a modified design in the blowout port is used. Essent,ially the apparatus consists of a modified oxyhydrogen burner, 1 ; packed quartz combustion tube, 2 ; with manometer fitting, 3 ; and safet,y blowout port, 4 ; condenser, 5 ; absorber section, 6 : and absorbent inlet system, 7, as shown in Figure 1. The blowout. port and manometer fitting
were placed on a side arm of the combustion tube to eliminate condensation in the manometer line. The glassware was purchased from the Greiner Glassblowing Laboratories, Los hngeles, Calif. Figure 2 is a schematic diagram of the specially designed gas control system. A pressure switch in the oxygen line actuates a solenoid in the hydrogen line so that a t pressures below a preset 12 p.s.i. 02-the flow of level-e.g., hydrogen is shut off. In addition the electrical control to the solenoid can be used a t all times to give instantaneous shutoff of the hydrogen. This is essential in the startup and shutdown procedure as described later. The manostat in the vacuum control system is used to control the vacuum a t a preset, level during the combustion step. Figure 3 shows a layout of gas, vacuum, and electrical controls which are necessary for efficient’ operation of the apparatus. Figure 4 shows a small sample reservoir suit,able for analysis of samples containing 1 to 2 p.p.m. of fluoride and higher. Reagents. T h e preparation of the spectrophotometric reagent has been described by Wharton (16). The reagent consists of zirconyl chloride octahydrate and SPL\DNS [4,5-dihydroxy3 - ( p - sulfophenylazo) - 2,7 - naphthalenedisulfonic acid, trisodium salt] in a 1 t,o 12 molar ratio in 0.4.Y HC1. Boric acid absorbent, 274, in deionized water. Procedure. Assemble the apparat,us as shown in Figures 1 to 3. Place the burner in the combustion tube and turn on the cooling air around the burner entrance. Adjust VOL. 3 6 , NO. 9, AUGUST 1964
1821
