ANALYTICAL CHEMISTRY
1606
of combinations. The three wave lengths were chosen in t,hc does not give positive results with resins made only with i.0phthalic or terephthalic acids. interest of permitting routine analysis of such mat,erials with a minimum of trial-and-error dilutions to obtain suitable absorbLITER4TURE (;WED ancc readings, and with adequate although not necessarily (1) Am. SOC.Testing Matei,ials, "A.P.T.SI. Standards," De&i:ition optimum accuracy. D 1307 and D 1306. 1954. Small samples of pure acids were used in these investigationr ( 2 ) Shrew, 0. D., and Hecthct,, l i . II., .\SAL. CHEM..23, 441 because of the low solubility of terephthalic acid in ethyl olrohol. (1951). (:O S w a m , 11, H., I h i d . , 21, 1448 (1949). The usual qualitative test used to detect alkyd rcFiiis .1:, W I I densing the dried film with phenol to form phcnol~~htli:tlriii I < b : c ~ ~ \ . b : uior rei-ieh XIarch 24, 1. .irr.eptrd 11ay 19, 1955.
Determination of Sulfur in Rubber Vulcanizates E. W. ZIMMERMAN', V. E. HART, and EMANUEL HOROWITZ National Bureau o f Standards, WasSinpton 25,
D. C.
-i conibustion method for rubber 'CI hich determines the sulfur evolved at 480" to 500" C. is compared with the fusion and the zinc-nitric acid methods. I n the combustion method an interaction occur3 hctw een the sulfur and the fillers present in the rubber. The effect of particular fillers with respect to this interaction is discussed. i value representative of the organically hnund sulfur in an extracted specimen can be obtained by the cornbustion method when no reaction takes place between the snlfur and the fillers during combustion. The fusion method yields results in good agreement with the total sulfur added in compounding the rubber samples. Except in the presence of barium compouncls, the zinc-nitric acid niethnd lihewise determines total sulfur. When hariuni compounds are present, barium sulfate is formed during the oxidation, and l o w values are ohtained for the total sulfur.
T
HE deterniination of organically bound sulfur in r u h l w
compounds presents a problem to the analytical chemist. A rubber vulcanizate ma>- contain sulfur that is prwent in th(h free state, sulfur that is conhined with the rubber or in other orgxnic compounds, and sulfur in inorganic compounds. The free sulfur can be determined after its removal by estraction. The sulfur that is coinhirlrd with the rubber and other organic mat,erial and the sulfur cont:tined in the inorganic fillers are usually determined together. h separate determinat,ion of the sulfur present in the inorganic fillers is then niade in ordry t o calculate the amount of sulfur that is organical1~-comhinetl. Combustion methods are often used to determine sdfiir. atid thr rapidity and accuracy of such methods make t'heni w i t : h k for many types of analyse?. Alt,temperatures of 1350' C. : ~ n d higher, the total sulfur in rubber vulcanizates can he dett:tmiined ( 2 ) . The rubber technologist, however, is usually more interested in organic sulfur than in total sulfur. Accordingly, an investigation of the combustion method at lox-er temperatures was undertaken. The compounds used in this study were also analyzed by the fusion and by the zinc-nitric acid methodn fol, romparative pnrposes. EXI'ERIMENTA L
A combustion method for the determinat#ionof sulfui, i l l i u t i l i c x i , may be divided into three phases: decomposing the specimen: collecting the evolved gases: and eetermining the amount of sulfur cvolved. Decomposing the Specimen. A rubber hydrocarbon can be distilled from a rubber compound belorv red heat. W'all ( 7 ) in 1
Present address, Aluminum Match Plate Corp., Buffalo, N. T.
Kork on the thermal decomposition of rubbers for mass spectroinetric investigations used a temperature of 400" C. in a high vacuum, because loner t'eniperatures did not complet,ely decompose the polvmers. I n analysis of GR-S carbon black masterbatches (5, 6 ) , 650" C. is used to remove the polymer in determining the ash and t'he carbon h1:tck. At 550" C. any lithoponc used in rubber compounds (komposes slightly with the evolution of hydrogen sulfide, which le t,o high results for sulfur; a t t$cmper.atures of 400' C. p j ~ o l ~of the ruhber always niay not be completed during the tinic: nllowed. Therefore, a temperature of 480" to 500' C . :qpcars to be optimum for the purpose of this investigation. The combustion of the ruhher sample was accomplishctl L)y using the two unit electric organic rombustion furnace shoivn in Figure 1. The 8-inch unit vas p1:tced at the exit end of thc conil)ustion tube and was maint,:tined a t a temperature of 850" t o (300" C. The 12-inch unit which x a s placed next to the srn:aller unit was maintained at a temperature of 480' to 500" C . The upper part of each unit was hinged to facilitate installing the combustion tube and the t,hermocouples. An unglazed porcelain McDanel combustion tube, 30 inches long, l1/{-inch outside diameter, 1-inch inside diameter, with a standard tnprt ~:tmpleinserter was found to be vel T o obtain a clean decomposition, it was necessary t o adjust the specimen size to a minimum compatible with the precision desired, to control the rate of devoniposition of the specimen so its to avoid minor explosions, anti t,o use sufficient oxygen to burn completely the volatilized organic material in order to avoid having soot enter the absorber. The specimens contained :Ipproximately 0.15 gram of hydrowrbon: and since the compounds contained about 65% hydrocarbon by weight, 0.25-gram ppecimens were used throughout thi. \r-oi,k.
IEUPFIInTURE CONTI1R
Figure 1.
Assembly of apparatus for combustion method
h specimen of ground r u l ) h vulcanizate vias accurately weighed, transferred. to a 10 X 75 mm. test tube, and tapped into the bottom with a glass rod. The test tube was laid in a porcelain combustion boat,, which as placed in the cool portion of the combustion tube wit,h the open end of the test tube facing the out,let end of the combustion tube. The sample injector n-as inserted into the large end of t,he combustion tube, the oxygen flow was adjusted to 1100 cc. per minute, and the combustion hont, was pushed int,o the cent,er of the 12-inch unit, which was maintained at about 500" C. The dense vapors that accompanied t,he initial decomposition of t,he specimen displaced t'he
V O L U M E 2 7 , NO. 10, O C T O B E R 1 9 5 5
1607
oxygen around the specinieii :tiid Inirned a t the mout,h of the test tuhe. Thus, the rubber wus permitted to decompose in an oxygen-poor atmosphere without :t localized temperature rise. Collecting the Evolved Gases. -4s the distillation of the rubbe], hydrocarbon occurred a t a relatively Ion- temperature. the gase. were passed through a high temperature zone to ensure completc caombustion. This was acc~oniplishi~tlwith tlie 8-inrh furnact~ unit maintained a t about 900" C. h close-fitting porous ceramic plug may be used in the high temperature zone to filter the gas or t o present more surface t o facilitate oxidation, but, is not essentid. Sirice sulfur trioxide \ v w present in the evolved gasps, t h e exit end of the Combustion tuhr \vas m:tintained a t a temperaturt, of :tt least 200" C. a3 suggested 1)y Hale and Muehlberg ( 4 ) . This \vas accomplished t ) ~ plaririg . the tuhe so that, the outlet tip was ahout. 2 inches from the edge of the hot zone, A Transit,(. baffle 1vit.h a hole just large enough to admit the thick portioii of the tip was mounted on the end of t>hefurnace to reduce the heat, loss in the furnace and protect the operator from the li(~i1 while manipulating the absorber'. -4 LI:rle-Muehlberg at)sortwi,, lubricated with heavy silicoiiv grease, vias connected t,o thv IlcDanel combustion tuhe 11). means of a stsndard taper joint. The absorber !vas chargpti with a solution prepared just, prior to use by mixing 4 ml. of 5% hydrogen peroxide solution, 18 ml. of 10% sodium chloride solution (to prevent fo:tmiiig during combustion), and 18 ml. of distilled w.itt.er. The 5% hydrogen peroxide solution \vas prepared by dilut,ing 30% AClS grade hydrogen peroxide that did not contain a stabilizer. This type of absorber, or even a battery of them, did not collect coinpletely the sulfur trioxide, Ivhich was seen passing t,hrough in the form of a fog. This loss ainounted to about 4yo of the evolved sulfur. However, v-hen a glass tube containing a filter of dry glass ~voolwas attached t,o the outlet end of the tower, t,his vapor was quantitatively collect'ed. Approximately 10 grams of ordinary glass wool, previously leached in a Ivarin 0.5% hydrochloric acid solution and washed with dist,illed a.:tter uiiM the washings were neutral to methyl red, was used t,o p:tck the filter tube. T h e exit end of the filt'cr tube was f i t t d \vit,h a rubber stopper containing a short length of glass t.uhirig to pi,ovide a connection to the drying columns and flow meter. Determining the Amount of Sulfur Evolved. After 10 minuter: the oxygen flow was shut off, the boat was removed from the conibustion tube, and the two absorbers \\--eredisconnected. The solution used to absorb the gases was quantitatively removed from the tower and glass tubing, and particular attention was paid to thorough rinsing of the fritted disk and the inside surface of the connecting tubes. The glass wool filter was rinsed by mounting the glass tube on a small suction flask and washing it with 125 ml. of distilled mater while using gentle suction. This w:is conhined with the solution already collected in a 400 ml. beaker, four (hops of methyl red indicator were added, and the solution was titritt,ed with standardized 0.02-1- sodium hydroxide. Thr. filter tube was prepared for the nest run hy rinsing with acetone, and drying with compressed air. RUBBER CO\IPOL~YI)S
Four rubber hatches ~ v e wc:irefull~-prepared on a part,s pci. weight, hasis t o reprePeri1 ? t i c s vuioii3 types of mixes and concen-
Table I.
Composition of Compounds
Batch designation Original mixes, parts b? r..v-. &= n. h.t. Pale crepe Sulfur Tetramethyltliiuraindisulfide [bis(dimethylthiocarbamovll 1 Phenyl-i-n'aphthylamine Diphenylguanidine Lead oxide Zinc oxide Fillers addeda
1
2
3
4
0 til';
100 413
100 7.17
I00 10.5
ion (I X 1 ,
1
1
J
50
50
Total. parts by weight Free sulfur added, 70
156.Y25 0.50L
165.13
C u r e : ,Time, Inin. remp., C.
30 140
30 1.50
Filler Identity Carbon black Calcium carbonate Barium carbonate Lit tiopone
I 1
10
.
1d
1E 1C 1D
2.ZO
30
50
15Y,l7
ltil 3
30 150
GO 160
4.50
C o m l ~ o u n dDesignation 2.4 3A 2B 3E 2C 3c 2D 30
ii 5 f )
4A 4B
ic
4D
trationx of Pulfur indicated in Table I. Each of these batches \vas divided into four groups, and to each group was added one of the four select,ed fillers. The fillers included carbon black (Thermax), calcium carbonate (Whiting), barium carborratr. and lithopone. The 16 rubber compounds, whose designations are listed in Table I, were analyzed for sulfur by the EuPion method and the zinc-nitric acid method described in ASTLI Standards on Rubber Product>s( 1 ) and the Federal Test Method Standard ( 3 ) . They n-ere also analyzed by the romb1lstion method described herein. The iesidues remaining after the cornbustiom of the compoundP iii groups A , B , and D were analyzed for sulfur by oxidation with a bromine-nitric acid solution and precipitation as barium sulftite. Those of group C were analyzed by the fusion method since the wet oxidation procedure ip inoperati& in the presence of t w i u m iwhonatc.
Table 11.
Sulfur Determined bj Combustion .\lethod
Compound
No. of Detn.
"6 Sulfu1 (.ii..)
1A 2A 3A 4A 1E 2B 3B
4
0.39 1.67 4 49 ( j 35 0.30 1,52 4.32 6 19
IC 2C
5 7 7
0 1 4 3 0
5R HC 5C
ID 20 3D
4 5 3 4 4 5 4
2 11 22 8 ii
Std. D e i . 0.033 0.037 0.078 0.036 0.031 0,029 0,062 0.14G
27 43 13 77
3fi 1 .YY 4 54 t i ?A
0 0 0 0 0
038 052 047 021 125
0.089
0.085 O.lR!i
RESULTS BY CO1lBUSTIOV lIETHOD
Table I1 gives the average values foi, the sulfur evolved during combustion from each of the 16 compounds and also the stanihrd deviations for the individual determinations. An anal) these standard deviations indicatrv the existence of two of precision. Determinations niude on samples of groups '1, R. :tnd C, \vhieh \Then compounded c~ontainedno inorganic sulfur, gave a standard deviation of the order of O . O i y o sulfur. Determinatione made on samples of group I), Tyhirh contained lii hot standard deviation of approximately 0.11yo sulfur. Thus, the presence of lithopone appears t o cause somewhat 1)oorer I~f:J)i'odUcibilit~ of results by this method of anal>-sis. X stiidy of the amount.< of d f u r found by combustion, as listed in Tal)lc 11, reveals systcni:ttic- differences in evolved eiilfiii. in tlie prwence of diflttrent types of inorganic fillers. The lowest values of evolved d f u r : o obtained ~ in samples containing barium carbonate, group C. The values for the sample? containing calcium carbonate ( B ) , carbon black ( A ) , and lithopone ( D ) , exceeded those found for the samples containing barium carbonate, on the average, by 0.18, 0.32, and O.4iYO, respectively. These differences in evolved sulfur are not appreciably influenced by the amount of added free sulfur. Except for t v o of the compounds containing lithopone, the evolved sulfur is less than the a,dded free sulfur. This fact, together with the observed tliffercrices in evolved sulfur for different fillers, can be interpreted in terms of varying degreks of combination of the added sulfur, exclusive of added inorganic sulfur, with the filler. Further evidence regarding this point is obtained from the study of the interaction between sulfiir arid fillers during combustion. IYTERACTION BETWEEN SULFUR AND FILLERS
Specimens from each of the rubber compounds were dissolved in hot o-dichlorobenzene (3),and the remaining inorganic residues
ANALYTICAL CHEMISTRY
1608 were analyzed for total sulfur by the fusion method. Thus, the amount of inorganic sulfur formed during vulcanization x a e determined. illso the residues from the combustion of each vulcanizate were analyzed for sulfur by a wet oxidation procedure, except in group C, where the fusion method was used. By comparing these two sets of values one can evaluate the degree of interaction between sulfur and fillers during combustion. These data are listed in Table 111. Examination of the values in colninn I leads to the conclusion that except in compounds containing lead oxide, very little sulfur combines during vulcanization as inorganic sulfur. For compounds in batch 1, which were compounded with only 0.5% of free sulfur, the formation of zinc sulfide during vulcanization did not occur to any appreciable extent. On the other hand, a comparison of the values in'columns I and I1 indicates that sulfur combines to an appreciable extent during combustion with zinc, lead, calcium, and barium compounds present in the vulcanizate. The largest amount of combination with the filler takes place in those samples containing lead oxide. When barium carbonate is present a moderate amount of combination takes place. The least combination occurs in samples which contain only carbon black, compounds 3A and 4A. For compounds l D , 3 0 , and 4 0 , which contttin sulfide from the added lithopone, less sulfide is recovered after combustion than was present initially. The results for sulfur determined by the combustion method and listed in Table I1 show that these three samples evolved more sulfur than the corresponding samples of groups A , B , and C. Compounds ID and 3D were
the only two that evolved more sulfur than was originally added in the form of free and organic sulfur. These results indicate that inorganic sulfides liberate some sulfur during the combustion. Compound 2 0 differs from the other members of group D in that more sulfide sulfur is found in the residue from combustion than was added in preparing the sample. Apparently the sulfur that combines with the lead more than compensates for that evolved from the lithopone. COMPARISON O F !METHODS
Table IV lists the sulfur added in compounding each sample and the amount of sulfur found by the three methods included in this study. Specimens from each rubber compound were analyzed by the fusion method to determine the total sulfur present; by the zinc-nitric acid method to obtain a combined value for the free, organically bound, and sulfide sulfur; and by the combustion method to determine the sulfur evolved during combustion. I n the column headed C o m b u d o n method and residue, the results in Table I1 and those in column I1 of Table I11 have been combined. I n interpreting this t3tile the following points should be borne in mind. For the compounds of groups .I and B, which contained no b:irium, the values obtained by the fusion method, zinc-nitric acid method, and comblistion plus residue procedure can be compared with the total amount of sulfur added. I n the zinc-nitric acid method, the presence of barium carbonate leads to low and erroneous results as the tmriiim sulfate formed during the oxidation phase of the analysis is not determined. The _________ -_ results of group C can be explained on this liasie. For the comTable 111. Interaction between Sulfur and Fillers during pounds of this group, a compariaon of the combustion plus Combustion residue values and those obtained by the fusion method can be Sulfur Found in Inorganic Sulfur Added in made with the total amount of sulfur added since no sulfate tvas Compound Compounding Samples, % ___Residue, 52 added in preparing these samples. For the compounds of group IO IIb Sulfide Sulfate Total D, both the zinc-nitric acid method and the combustion plus residue procedur? determine all but the sulfate sulfur. An analysis of the data shows that the fusion method is free of 0.02 0.30 1B 0 0 0 systematic errors and that its reproducibility is reflected by a 0.03 1.02 2B 0 0 0 standard deviation of 0.1% sulfur. The zinc-nitric acid method, 0.01 0.12 3B 0 0 0 0 0 0.02 0.14 4B 0 where applicable, tends t o give results that are low, on the average, by 0.09% sulfur. I t s reproducibility is characterized by a standard deviation of 0.1% sulfur, which is comparable t o that of the fusion method. The values obtained by the combustion plus 0.15 6.13 2.92 1D 3 10 3.05 residue procedure appear to be free of systematic errors for the 3.84 2D 2.94 2.90 fi.59 3.18 6.06 30 3.05 3.01 6.18 2.84 compounds of groups 8 , B , and C. For compounds of group D 5.97 5,915 2.72 4D 3.01 2.96 this procedure yields values which are consistently low (on the a Total sulfur determined in residue remaining after dissoliing 1-ulcaniaed rubber in o-dichlorobenzene. average, by 0.23% sulfur), when compared t o the sulfur added, b Sulfide sulfur in nonvolatile residue remaining from the combustion exclusive of sulfate sulfur. analysis. For group C, inorganic sulfur was determined by the fusion method. The values listed in the last column repre-__ sent the sulfur evolved during combustion. Column I1 in Table I11 lists the inorganic sulTable IV. Comparison of Values for Sulfur Foumd by Different fur formed during the course of the conibusAnalytical Procedures tion. For the compounds of groups B , C, and D ___ Sulfur Found, % __ where reaction takes place with the filler during Combustion Combuscombustion, the combustion method is only semiSulfur Added. % Fusion Z n T H X O l method tion ComFree Sulfide Sulfate Total method method -residue method pound quantitative. Among the compounds of group A , 0.50 0.44 1A 0.50 n 0 0.47 0.55 0.39 qainples 38 and 4A contained only carbon black 2.50 0 n 2.50 2.53 2.36 2A 2.27 1.67 'ti :I filler and satisfactory results were obtained 4.50 0 0 4.50 4.49 4.45 4.51 4.49 3A 41 6.50 0 0 6.50 6,41 6.39 0.42 0.35 by the combustion method for these samples. 1B 0.50 0 0 0.50 0.46 0.48 0.60 0.30 For samples la, and 2d which contained zinc 2B 2.50 0 0 2.50 2.13 2.26 2.54 1.52 4.50 0 0 4.50 3B 4.55 4.44 4.44 4.32 oxide and lead oxide, respectively, the combus4B 6.50 0 0 6.50 6.50 6.36 6.33 6.19 tion method yielded low results. 1c 0.50 0 0 0.50 0.50 0.01 0.66 0.27 I n conclusion, a value representative of the 2C 2.50 0 0 2.50 2.55 0.01 2.57 l,45 3c 4.50 0 0 4.50 4.38 0.11 4.50 4.13 organically bound sulfur can be obtained by the 6 . 5 0 0 0 6.50 4c 6.59 1.40 6,50 5.77 combustion method for extracted samples that, 1D 0.50 3.10 3.05 6,65 6.66 3.62 3.48 0 56 20 2.50 2.94 2.90 8.34 8.33 5,27 5.17 1.99 cont,ain only carbon black as a filler and when 30 4.50 3.05 3.01 10.56 10.58 7.58 7.38 4.54 40 6.50 zinc oxide and lead oxide are both absent. For 3.01 2.96 12.47 12.14 9.39 9.11 6.39 the other samples a combinRtion of extraction, ~
V O L U M E 27, NO. 10, O C T O B E R 1 9 5 5 a total sulfur method and the o-clichlorol,rnzeiie solution procedure (S), appears to be required for determining organic sulfur reliably. .iCKNOWLEDGMENT
The authors wish t o thank John hlandel of the Testing and Specifications Section for his statistical analysip of the dats. LlTERATURE CITED
1609 ( 2 ) British Standards Institution, Bull. 903, Method 3.14, p. 27, 1950. (3) Federal Testing Method Standard. S o . 601, .\lethods 1G231 and 16241. (4)
Hale, C. H., and SZuehlberg, W.F., I s n . ESG.CHEM.,AXAL.ED., 8, 317 (1936).
( 5 ) Linnig, F. J.,Milliken, L. T., and Cohen, R. I., J . Research .\-atZ. B u r . Standards, 47, 135 (1961). ( 6 ) Reconstruction Finance Corp., Office of Production, Synthetic Rubber Div., "Specifications for Government Synthetic Rubbers," Washington, D. C., rev. ed., (October, 1952). FVall, L. d., J . Research, .Vatl. B u r . Standards, 41, 315 (1948).
"' I"\
(1) Ani. SOC.Testing Materials Philadelphia, Pa., Part ti, Designa-
tion D-297-50T, pp. 63-4, 1952.
RECEIVED for re\.iew .ipril5, 19.55.
Accepted May 26, 1966.
Densities and Refractive Indexes for Ethylene Glycol-Water Solutions EDWARD T. FOGGI, A. NORMAN HIXSON, and A. RALPH THOMPSON2 University o f Pennsylvania, Philadelphia, Pa.
The lack of agreement aniong previouslj pui)lished data indicated the need for precise anal) tical data for mixtures of ethj lene glycol (1,2-ethanediol) and water. Investigation of gl?col purification by vacuum distillation defined the necessit? for extreme care in prekenting contamination with trace amounts of oxidation products. Densities at 23" C. and refractive indexes at 20" C. w-eredetermined for niiutures of highly purified ethylene gl?col and water. ?'he density data provide a basis for analysis to within +0.11% by weight, whereas refractive index determinations yield analyses accurate to within f0.03 weight %. Refractive index is not a linear function of weight per cent compoSition. as is commonl? asqumpd for this sJsleni.
I
N TIIE course of a recent distillation study irivolving t'hc
et,hylenc glycol-n-ater syst,em a precise analytical method was of critical importance. Variations in published valiies for the density and refractive index of purified ethylene glycol suggested the presence of trace impurities, since the range of values v a s considerably in excess of that which would be expected from a series of independent determinations on identical mittcrixls. Therefore, purification by vacuum distillation was studied froni the standpoint of identification and subsequent elimination of trace cont,aminauts. Once a satisfactory distillation procedure was found, densities and refractivc indexes were determined for the aqueous glycol system over t.he eutirr composition rmigc.
purified ethylene glycol. Similarly, the refractive index, %go, varied from'1.13179 t o 1.43182 with the higher value being the most common. Extrapolating to zero water content led to a value of 1.43188 for purified glycol as compared t o previously published values ranging from 1.4304 ( 1 ) to 1.43192 (IO).
In general, there are two primary sources of glycol contamination, both of which tend t o lo\wr density and refractive index values, and which could well account for the wide range of reportwl values for density and refractive index. The most obvious is t.he :Ilniost unavoidable presence of small quantities of water; in much of the early literature no water determinations were reported and prohably this accounts for many of the discrepancies. The second class of contaminant,s consists of oxidation pmducts: aldehydes and acids. It was shown during the first attempts a t purification that the oxidation reaction was platinum catalyzed; however, t,race amounts of aldehydes were detected (Schiff hasej even when all-glass equipment was used. Repeated purging of the distillation equipment xith oxygen-free nit,rogen prior to st,art-up eliminated the formation of analyzable quantities of 3 Idehydes. Contamination hy this mechanism would hc a diptinct possildity in much of t>hepreviously published work and very probable in those cases n-here a,n air bleed was introduced into the still pot to promo Water used in the preparation of the glycol solutions used in this work rras freshly distilled and had a specific conductivity of the order of 10-6 ohm-' em.? As an added precaution, t.he n-at.er was boiled to remove dissolved gases and then cooled 11-ithout apit,ation immediately prior to use.
PURIFI(:.ZIION OF >lATERI.&LS
PREPARATIOW OF SOLUTIOIVS
Tecliriical grade. 99.570, ethylene glycol was fractionated a t 7 to 10 mm. of mercury absolute pressure and with a reflux ratio of 10 to 1 in a nitrogen-blanketed, adiabatically operated, packed column (1 inch in diameter and packed to a depth of 36 inches with glass helices "16 inch in diameter). Only the middle third of the const,aiit boiling point distillate was collected. Iieproducibility of the product was adequate as evidenced by the constancy of the physical proprl,ties. Of elwen lots thus purified. thv densities a t 25' C. varied from 1.1098 to 1,1099 grams per nil. with the average k i n g 1.10982 grams per ml., as compared to previously published values which range from 1.1097 (8) t o 1.1110 ( 4 ) with the most probable value. according t o Curme and Johnston ( S ) , being 1.10986 gr:tms pcr ml. Despite all precaiitions taken to prevent, water contamination, t8he purified glyc.01 analyzed (by Karl Fischer reagent) 0.07 f O . O l ~ o(weight') water. Correcting for the presence of water b y extrapolation rtwilted in an :tverage density of 1.10988 grams per ml. for the
Solutions of known composition were prepared by injecting approximat? amounts of purified glycol (0.07% water) and water into dried, stoppered 60-ml. vaccine bottles. The exact compositions were determined by n-eighing to 0.1 mg. Hypodermic syringes used to transfer the glycol mere dried a t 110' C. and then allowed to cool in a desiccator until used. Since the smallest amount of either component was 2.7 grams. the compositions n-ere known to a t least 1 part in 27,000 or 0.004 veight 7'
1 Present address, E. I. d u Font de Kcinours & Co., Inc., T i l i n i n g t o n , Del. 2 Present address, Department of Chemical Engineering, University of Rhode Island, Kingston, R . I.
D E S S I T l AND REFR.ZCTIVE INDEX DETEKRZINATIOYS
Density measurements were made in 10-ml. Weld-type. capped, specific gravity bottles which had been calibrated with boiled, distilled water: Temperature control was obtained by partially submerging the bottles in a 5-gallon constant ten>perature bath controlled a t 25.00' + 0.03" C. The maximuin error resulting from uncertainties in the volume calibration of the specific gravity bottles T o d d be *0.00009 gram per ml. However, strict adherence to a standardized procedure resulted in duplicate measuremente having a maximum deviat,ion of .000011 gram per ml.
