Determination of Alkoxyl Groups in Cellulose Ethers - American

pigments and latex. Some problems require the use of metallographic methods; in many cases where vertical illumination is used polarized light is serv...
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direct and positive means of determining the existence of distinct phases and certainly one of the most rapid. Microcataphoresis methods have been used in the study of certain pigments and latex. Some problems require the use of metallographic methods; in many cases where vertical illumination is used polarized light is serviceable. Fluorescent microscopy is an elegant method, revealing information which is otherwise unobtainable (26, 28). Although many problems possess traits, in common, a large proportion of cases display new features which require strictly individual and original treatment. This paper presents evidence that the microscope and microscopic methods disclose invaluable information, far less readily obtainable by other means and indeed frequently unobtainable by procedures other than those peculiar to the niicroscope.

Literature Cited Allen, IND.EXG.CHEM.,ANAL.ED., 2, 311 (1930). Includes bibliography of rubber sectioning up t o 1930. Ibid., 14, 92 (1942).

Allen, Report to Am. SOC.Testing Materials Subcommittee on Particle Size and Shape (July 5 , 1927). Allen and Schoenfeld, IND.ENG.CHEM.,25, 994, 1102 (1933). Am. SOC.Testing Materials, Proc. Am. SOC.Testing Materials, 35. 497 (1935). - -,



Vol. 14, No. 9

INDUSTRIAL AND ENGINEERING CHEMISTRY

Ibid.; p. 506. Ames, J . Roy. Microscop. SOC.,264, 265 (1923). Breuil, Compt. rend., 140, 1142 (1905). Chamot, J. IND.ENG.CHEM.,10, 60 (1918). Chamot and Mason. “Handbook of Chemical MicroscoDv” 2nd ed., Vol. I, p. 408-28, New York, John Wiley & Sons

Co., 1938.

(11) “Colloidal Carbons. (12) (13) (14) (15)

(16) (17) (18)

Particle Size and Shape as Revealed by the Electron Microscope”, Vol. 11, Columbian Carbon Research Laboratories, New York, 1940. Depew and Ruby, J. IND.ENG.CHEM.,12, 1156 (1920). Dieterich, IND.ENG.CHEM.,ANAL.ED.,2, 102 (1930). Endres, I n d i a Rubber World, 68, 635 (1923). Evans, I n d i a Rubber J.,64, 815 (1922). Gage, “The Microscope”, 16th ed., p. 153, Ithaca, N. Y., Comstock Publishing Co., 1936. Gehman and Morris, IND.ENG.CHEM., ANAL.ED.,4, 157 (1932). Geohegan, Paper Trade J., 88, No. 23, 63 (1929); 90, No. 10, 67 (1930).

(19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30) (31) (32) (33)



Green, J . Franklin Inst., 192, 654 (1921). Green, J. IND.ENG.CHEM.,13, 1130 (1921). Green, Chem. & Met. Eng., 28, 55 (1923). Hardman, I n d i a Rubber World, 68, 711 (1923). Haslam, Rubber Age, 32, 89 (1932). Haslam and Hall, J . Franklin Inst., 209, 777 (1930). Hauser, Kautschuk, p. 7 (Jan. 1926). Hauser and LeBeau, Ibid., 10, 113 (1934). Henri. Gummi-Zta.. 20. 1227 (1906). Morris, IND. ENG. CHEM.,26,’107 (1934). iV. J . Z i n c Activator, 2, 51 (1936).

Park and McClellan, IKD.ENG.CHEM.,30, 704 (1938). Parkinson, Trans. Inst. Rubber I n d . , 16, 87 (1940). Perrott and Kinney, J . Am. Ceram. Soc., 6 , 417 (1923). Pohle, Memmler, “The Science of Rubber”, pp. 637-75, 1Vew York, Reinhold Publishing Corp., 1934. (34) Roninger, IND.EKG.CHEM., ANAL. ED.,5 , 251 (1933). (35) Siedentopf and Szigmondy, Verhandl. dezrt. physik. Ges., 5 , 209 (1903); Ann. Physik, (4) 10, 16 (1903). (36) (37) (38) (39) (40)

Stutz, J . Franklin Inst., 210, 67 (1930). Stutz and Pfund, IND.EXG.CHEM.,19, 51 (1927). Sutcliffe, J . R o y . Microscop. Soc., 260, 245 (1922). Vogt and Evans, IND.ENG.CHEM.,15, 1015 (1923). Zimmerman, Rubber Age, 12, 130 (1922).

PRESENTED before the Division of Microchemistry at the 97th Meeting of the AMERICAN CHEMICAL SOCIETY, Baltimore, Md.

Determination of Alkoxy1 Groups in Cellulose Ethers E. P. SA3ISEL

AND

J. A. RICH.IRD, Cellulose Products Diiision, The Dow Chemical Company, 3iidland, llich.

The Viebock modification of the Zeisel method for the determination of alkoxyl groups has been studied in detail with specia1 reference to the application of the method to the lower alkyl ethers of cellulose. A n improved apparatus is shown and improvements which have been made in the technique are described. Particular attention is given to the use of solvents, such as phenol and organic acid anhydrides. It is not recommended that these be used. Attention is called to the necessity of using hydriodic acid of 56.5 to 57 per cent concentration when water-insoluble ethylcelluloses are to be determined.

T

HE rapidly increasing commercial importance of ethylcellulose and methylcellulose makes desirable a more universally acceptable method for the accurate determination Of alkoxyl groups O f CellUlOSe ethers. It iS particularly desirable that the method be suitable for a wide range of ethoxy1 and methoxyl values. During the past six years, the sem~m~cromethod described herein has been used by the authors. The conclusions arrived a t are based upon routine daily determinations per-

formed on methyl- and ethylcelluloses of widely varying degrees of substitution. The original Zeisel method ( I O ) as modified by Pregl ( 6 ) has been generally adopted for determinations on a micro scale. It consists in heating the ether sample with a strong solution of hydriodic acid to form an alkyl iodide, which, by means of a stream of carbon dioxide, is swept through a condenser and finally absorbed in a solution of silver nitrate. The resulting silver iodide is separated and weighed. This procedure is cumbersome and is subject to the usual errors in a gravimetric technique, The method was adapted to ’volumetric analysis by Yiebock and Schw-appach (8) and T’iebock and Brecher ( 7 ) who substituted a mixture of bromine, acetic acid, and sodium acetate for the silver nitrate in the absorption tubes. Ethyl iodide absorbed in this mixture is oxidized to iodate, as shown in Equations 1 to 3. After reduction of the excess bromine with formic acid, the iodate is determined iodometrically, using potassium iodide and standard thiosulfate as shown in Equations 4 and 5.

+

+ +

ROQH, HI = CzHJ ROH C&I Brp = CpHbBr IBr IBr 2Br2 3H20 = HI03 5HBr HI03 5KI 5H+ = 312 3Hz0 5Kf Io 2YapSpOa = 2NaI NapSaOs

+ + + + + +

+

+

+

+

Apparatus The details of the modified Zeisel apparatus are shown in Figure 1 and the complete assembly is shown diagrammatically in Figure 2. The apparatus consists of a boiling flask, A , fitted with side arm for introduction of carbon dioxide and connected to a column, B , which serves to separate aqueous hydriodic acid from the volatile alkyl iodide, which then passes through an aqueous suspension of red phosphorus in scrubber trap, C, and is ab-

ANALYTICAL EDITION

September 15, 1942

751

sorbed in the bromine-acetic acid solution in absorbing tube D. A secondary adsorber, E, also containing bromine-acetic acid, ensures complete absorption of the alkyl iodide. Many changes in the apparatus were made before the one shown in Figures 1 and 3 was finally adopted. Except for having a slightly smaller volume, the reaction flask, A , is the same as that suggested by Clark ( 1 , Z ) . An apparatus having a long Vigreux column in conjunction with a trap containing glass wool instead of water was successfully used for several years. However, the glass wool was subject to attack from the hydriodic acid and, after a period of time, the effectiveness of the trap was somewhat lessened. More recently, it was found that a straight column and a water trap provide a simpler apparatus from the standpoint of construction and operation. The water trap, C, is similar to that of Viebock ( 7 , 8 ) ,except it has no removable ground-glass joint. This trap is filled from the absorber end of the apparatus. The advantage of this type of trap is that there is no possibility of leaks through a ground-glass joint at the top. The use of water to scrub out vapors of entrained iodine and hydriodic acid was first employed by Clark (1, 2). Although this modification can be used succesefully, an aqueous suspension of red phosphorus will eliminate any possibility of iodine being carried over into the absorbers. Recent experiments indicate that this method will give satisfactory results viith materials containing considerable amounts of sulfur.

11.5 cm.

'

k

Imm.

A

CAPILLARY

9 cm.

OF MODIFIED ZEISELAPPARATUS FIGURE 1. COSSTRUCTIOSDETAILS

P r e s s u r e Gauge

-73

G 02

c ylinder-4

Elecfric Heater

I

APPARATUS FIGURE 2. ASSEMBLYOF ETHOXYL

bressure

Equalizer

INDUSTRIAL AND ENGINEERING CHEMISTRY

152

Vol. 14, No. 9

TABLEI. ETHOXYL DETERMINATIONS AT &MINUTE REACTION TIME

-

(Average of s t least 2.

p-Ethoxy-

bensoic aoidb

Added Reagents Nolle 2 . 6 0 0 . of Dhend 0 . 5 0 0 . of phenol 0 . 5 cc. of phenol

+ 0.5

CC.

Calod. 27.1 27.1

of

propionic anhydride 0.4 00. of pro~?ome anhydride 1 . 0 DC. of propmnic anhydride Blank

~

Found

27.0.27.1 26.8.26.6 26.9 26.9

..

..

.. .. .. ..

Reaction mixture. 6 00. of HI, sp. gr. 1.69) Gelatin c*peu1es* -open Ci1aaa CapauleaEthylEthylEthylcellulose cellulose p-Ethoqoellulose p-Ethoxydiphenyl' l o t 4521 lot 996 benroic %old& lot 4521 Found Calod. Found Calod. 11.4 22.6

22.7 22.7

.. ..

.. ..

..

48.5.48.8 48.3 48.1

..

48.0 47.6

..

27.2 27.2

.. ..

.. ..

47.6 4.3.5 46.6

..

47.1 48.4

..

..

..

"

47.1 47.7

..

..

..

..

0 . 3 &.'of 0 . 1 N'NanS301

27.1 27.1

Ethyl-

oellulose lot 996

. .. ~ * ." ~

.. .. .. ..

.. 1,

..

. T ~

cI

~~

The use of ground-glass joints throughout is advisable; however, it is best to use as few joints of any kind as possible. I n the apparatus proposed in this paper (Figures 1 and 3) only one joint is used between flask A and the final absorber, E. E is attached to the side arm of the first absorber by means of a wire loop, making assemblage easy. A view of a single unit is shown in Figure 3 and a battery of any convenient number of sucii units may"be Fun a! thes?me time. single cylinder, as indicated in I sq. inch (5 pounds p ersquare

,

inch) is obt gas is led through a surge chamber t o mmmiae pressure iiuctuations, then through an empty flask to a manifold containing the required number of outlets. From each outlet B rubber tube equipped with a stopcock and a capillary tube containing a cotton wadding filter, Leads t o A. The heating bath consists of a long oil bath electrically heated and thermostatioally controlled, with openings in the top hrge enough to allow immersion of the flasks in the oil approximately to the level of the contained hydriodic acid

TABLE 11.

METHOXYL DETERMINATIONS A T 40-MINUTE REACTION TIME

(Average 01 a t least 2.

Added Reagents

20.6 20.1

None

2.5 ec. of phenol a

Vanillin, Eastmaii

TABLE

Reaction mixture 8 cc. 01 HI, SP. u. 1.69) Methyloellvlose Lot Vanillin*. Gelstin X-1097 Capsules Gelatin Open glass Found Calod. capsules capsule8

c. P.

b 0

30.9 30.8

grade m. p. 81-82' C.

O F HYDRIODIC ACID CONCENTRlTlON UPON 111. EFFECT ALKOXYL CONTENT

Hydriodio Acid sp. sr. at Conon. EthylMethyl25 C. % by d.oellulosen oelluloses

a

31.1 31.0

20.4 20.4

1.694

56.7

1.672

55.8

1.665

55.5

48.6 48.4 47.1 47.4 47.7 47.6

31.0 31.1 31.0 30.9 31.1 30.9

p-Ethoxybenzoic Acida Found Caled. 27.0 27.1 26.9 26.9 26.9 21.0

27.1 27.1 27.1

Ethoeel lot 4521.

Methoekl. lot M-1097. P.. m, p. 196-198* C.

Esstrnan c.

Experimental Work

I Cou~1eeu.Dow Chemtcal Ca,

FIGURE 3. INDIVIDU~L. UNIT

This investigation has been devoted principally to a study of factors which affect the accuracy and simplicity of the method of analysis of methyl- and ethylcelluloses. The effect of hydriodic acid concentration was first studied. The effect of solvents, such as phenol, acetic anhydride, and propionic anhydride, alone and in various combinations, ,upon the determination was studied. Experiments were conducted , I .. ,.,.I-~ ~, . -.:LL ^I^^^ "-to compare m e suraamzy 01 geibuii wpauira w n u ~ L W D ~ V U tainers for use in weighing samples. T h e analyses made upon samples of ethylcellulose, methylcellulose, and crystalline organic compounds t o determine these effects are listed in Tables I and 11. T h e effect of concentration of hydriodic acid upon the value of the alkoxy1 content is shown in Table I11 for water-insoluble

ANALYTICAL EDITION

September 15, 1942

ethylcellulose, water-soluble methylcellulose, and a pure sample of p-ethoxy-benzoic acid. The data show t h a t small variations in hydriodic acid content do not affect the reproducibility of values obtained with methylcellulose or with pethoxybenzoic acid, materials which are easily dissolved by the hydriodic acid, b u t do give low ethoxyl values for ethylcellulose when the specific gravity of the hydriodic acid used is less than 1.69 a t 25" C.

1

I 44'

I

'

I

'

l

l

I

PHENOL ADDED

I

!

30 40 RLACTlON T I M E (N MINUTES

60

753

open glass capsule (3) allows the sample t o spill and float on the surface of the liquid with the danger of some of the material sticking to the sides of the flask and charring. The use of a closed glass capsule involves the hazardous problem of breaking it inside the flask. Much has been written ( I , 3, 4, 6,9) about the advisability of using some sort of agent to aid in the solution of the sample. Experiments using phenol, acetic anhydride, and propionic anhydride were conducted to determine the effect of the addition of these materials to the reaction mixture upon the determination of methoxyl and ethoxyl a t various reaction times. The results are shown in Tables ITr and V and Figure 4. The data of Table IV indicate that slightly lower ethoxyl values are obtained on ethyl cellulose when phenol is used. On p-ethoxybenzoic acid and p-ethoxyacetanilide, phenol exerts a retarding effect a t 30 minutes' reaction time. However, a t the recommended 40 minutes' reaction time, phenol has no effect when these two ethers are used as reference compounds. X h e n p-ethoxydiphenyl is used as the reference compound, phenol is required because of the difficulty of dissolving this unsubstituted ether in the reaction mixture. The data of Table V shorn that phenol is without effect upon the determination of methoxyl content of methylcellulose or of vanillin as the reference compound. Both materials are readily attacked by the hot concentrated hydriodic acid. Except for a few very insoluble compounds like pethoxydiphenyl, hydriodic acid alone is very satisfactory, especially when freshly distilled material having a concentration of 56.5 to 57 per cent is used with a gelatin capsule for weighing the sample and transferring it to the reaction flask. The experience of the authors is that phenol, acetic anhydride, or propionic anhydride give slightly low results, as the data of Tables I and I1 show.

FIGCRE 4. EFFECT OF PHENOL ON DETERMINATION OF ETHOXYL AT VARIOUS RE.4CTION TIMES TABLE

The rest of the investigation was devoted to the deterniination of the effects which other variations in the method produced upon the accuracy of the method when applied to methyl- or ethylcellulose. The effect of variations in the sample container used and of the addition of phenol and/or propionic anhydride to the reaction mixture is shown b y Table I for determinations on ethylcellulose. The data also indicate the degree of reproducibility of results when 56.5 t o 57 per cent hydriodic acid (sp. gr. 1.69 to 1.70 a t 25' C.) is used. Similar data are given in Table I11 for methylcellulose. The gelatin capsule gives a slight b u t uniform titration of only 0.2 t o 0.3 cc. of 0.1 N sodium thiosulfate compared t o about 0.1 cc. for glass. Uniformly higher results were obtained on both cellulose ethers when the gelatin capsules were used instead of open glass cups for adding the sample to the concentrated hydriodic acid. Of the many means suggested for introducing the sample into the flask, the use of the gelatin capsule has proved to be the most reliable. It functions to protect the sample from any action by the hydriodic acid until the boiling flask can be joined to the rest of the apparatus. As soon as the reaction mixture is heated, the gelatin dissolves completely, leaving the sample free to be decomposed by the acid. Capsules sampled over a period of 3 years' purchases (I'arke, Davis & Company, Detroit, Mich.) gave a blank of llat more than the 0.3 cc. noted in Table I. Other methods for introducing the sample are open t o the following objections: Cigaret paper ( I ) causes excess fuming of the hydriodic acid, tin foil (6) is awkward to use, while an

OF PHENOL ON DETERMINATION O F ETHOXYL Iv. EFFECT Time of Reaction 30 min. 40 min. 60 min.

Added Reagents

Saniple Ethylcellulose Lot 5419

Sone Phenol"

Lot 4521

None Phenola

Lot 4609

Sone Phenol"

p-Ethoxybenzoic acidb

None Phenola

p-Ethoxyacetanilidee

Sone

'

Phenol0

44.7 44.7 44 8 44.3 47.5 48.7 47.7 48 4 51.7 51.5 49.6 50.1 26.9 27.1 25.4 24.5 24.9 24.9 24.4 24.8

v.

a 2.5 c c . of D o w S., P . henol added. b p-Ethoxybenzoic acid E a s t m a n c. P. grade, 0

D o w U. S. P. acetphehetidin, m. p . 135' C.

T.4BL.E

v.

Sample

EFFECTOF

45.6 45.8 45.0 44.8 48.8 48.5 48.4

48.3 51.5 51.6 50.8 51.4 27.1 26.9 27.0 26.9 24.9 24.9 25.0 24.9

METHOXYL

2 . 5 cc. of Dow U S P phenol added.

b Vanillin, E a s t m a n c. P. grade, m. p. 81-82'

..

.. ..

..

..

.. ..

27:1

..

..

.. .. ..

.. ..

.. .. .. ..

2i:1

DETERMINATION OF

Time nf Reaction 30 min. 40 min.

Methyl

a

.. .. ..

45.5 45.3 45.0 45.2 48.7 48.8 48.7 48.4 .5l . 9 51.8 50.9 51.2

m. p . 196-198' C .

PHENOL O S THE Added Reagents

Calcd.

c

Calcd.

754

INDUSTRIAL A N D ENGINEERING CHEMISTRY

Vol. 14, No. 9

Recommended Analytical Procedure The method described in the following paragraphs was developed from the results of the preceding experiments. REAGENTS.1. Potassium acetate in acetic acid. Dissolve 100 grams of c. P. anhydrous potassium acetate in 1 liter of solution containing 900 cc. of glacial acetic acid and 100 cc. of acetic anhydride. 2. Dissolve 5 cc. of bromine in 145 cc. of the 10 per cent solution of potassium acetate in acetic acid. Prepare this solution fresh daily. 3. Potassium iodide, c. P. grade. 4. Sodium acetate. Dissolve 250 grams of c. P. anhydrous sodium acetate in 1 liter of distilled water. 5. Formic acid. Analytical reagent grade, 90 per cent, sp. gr. 1.20. 6. Hydriodic acid. c. P. constant-boiling mixture, b. p. 126" to 127" C. (57 per cent hydriodic acid), made very pure by the method presented herewith.

7. Prepare 0.1 N sodium thiosulfate and standardize against 0.1 N iodine, which in turn is standardized against 0.1 N arsenious oxide or potassium iodate (Bureau of Standards). 8. Sulfuric acid, 10 per cent. Add 60 cc. of the concentrated acid to 940 cc. of distilled water. 9. Aqueous suspension of red phosphorus. Add about 30 mg. of c. P. red phosphorus to 50 cc. of distilled water. 10. Carbon dioxide. A commercial cylinder of the gas equipped with a reducing valve is a convenient source. PROCEDURE. Unless they are already finely divided, grind ethylcellulose samples in a Wiley micro laboratory mill and then oven-dry a t 105' C. for one-half hour. Fill the trap by pouring a small amount of an aqueous suspension of red phosphorus through the cup above D. Follow with a water rinse, using sufficient liquid to make the trap about half full. Add 6 to 7 cc. of the bromine-potassium acetate-acetic acid solution to the first receiver and 10 to 12 cc. to the second. The latter is attached to the a p paratus by means of a wire loop. Weigh carefully a 50- to 60mg. sample in a gelatin capsule (Parke, Davis size 0) and drop into the boiling flask. Add a few small glass beads and chips of clay plate and finally 6 cc. of constant-boiling 57 per cent hydriodic acid. Immediately attach the flask to the condenser, using a few drops of the acid to seal the joint. Bubble a slow stream of carbon dioxide through the side arm of the boiling flask (two bubbles per second are satisfactory), place the boiling flask in a 150' C. oil bath, and heat for 40 minutes. Wash the contents of the receiver into a 500-cc. flask containing 10 cc. of the sodium acetate solution. Dilute to 125 cc. with water and add formic acid, dropwise, with swirling, until the brown color of the bromine discharges, then add 3 additional drops. This usually requires a total of 12 to 15 drops. After standing 3 minutes, add 3 grams of potassium iodide and 15 cc. of 10 per cent sulfuric acid. Titrate the liberated iodine with 0.1 N sodium thiosulfate and apply the correction for a blank. Net cc. of 0.1 N Na2S203x conversion factor X 100 = % alkoxyl Weight of sample (corrected for ash and moisture) Factor for OCH3 = 0.000517, for O C Z H = ~ 0.00075

Discussion and Summary The method as described has been used in this laboratory for several years, both as a routine control test for ethyl- and methylcellulose and as a n accurate analytical procedure for determining ethoxyl and methoxyl values in crystalline organic compounds such as vanillin and p-ethoxybenzoic acid. It is evident that with cellulose ethers i t is neither necessary nor advisable to use a solvent in addition to the hydriodic acid, but by the time the analysis is completed, the compound being determined must be completely decomposed. With a very few organic compounds which are especially resistant to attack the use of a solvent like phenol or propionic anhydride is necessary. Severtheless, the procedure as given is generally applicable to the lower alkyl ethers. X HI Further research is being done on this method to modify it FIGURE5. SPECIFICGRAVITY OF CONCENTRATED HYDRIODIC for analyzing propyl and butyl ethers of cellulose. The method has not been applied successfully t o benzylcellulose, ACIDAT 25" C. because the boiling point of the benzyl iodide is higher than that of the hydriodic acid used. Add 70 grams of c. P. red phosphorus to a 2-liter three-necked round-bottomed flask which has been fitted with a reflux condenser, dropping funnel, and thermometer. Fill the flask half full with Literature Cited distilled water and heat with a low flame. Slowly add, through the dropping funnel, a solution of 800 grams of iodine in 800 cc. (1) Clark, E. P., J . Assoc. Oficial -407.Chem, 15, 136-40 (1932). of hydriodic acid. Heat until the mixture boils (b. p. 127" C.) (2) Ibid., 22, 100 (1939). and continue boiling for one-half hour. Allow the excess red (3) Elek, A., IND. E X c . CHEM.,A N A L . ED.,11, 174-7 (1939). phosphorus to settle and decant the hydriodic acid-phosphorus (4) Manning, R. J., and Nierenstein, M., Ber., 46, 3983-4 (1913). mixture into a suitable distillation flask equipped with an ef(5) Nierenstein, M., Analyst, 51, 456 (1926). ficient fractionation column. I t is necessary t o use an all-glass (6) Pregl, F., "Die quantitative organic Mikroanalyse", pp. 153-61, apparatus equipped with ground-glass joints. Pass a slow stream Berlin, Julius Springer, 1917. of carbon dioxide through the apparatus during the distillation. (7) Viebock, F., and Brecher, C., Ber., 63B, 3207-10 (1930). The inlet tube should dip beneath the surface of the liquid. Con(8) Viebock, F., and Schwappach, A., Ibid., 63B,2818-23 (1930). tinue the distillation and collect for use only that portion which (9) Weishut, F., Nolonatsh., 33, 1165-72 (1912). has a specific gravity between 1.690 and 1.700 (Figure 5 ) . Store (10) Zeisel, S.,Ibid., 6, 989-96 (1885). in small brown glass-stoppered bottles previously swept out with carbon dioxide, and seal stoppers with melted paraffin. Store in a PRESENTED before the Division of Cellulose Chemistry at the 103rd Meeting dark place. of the AMERICANCHEMICAL SOCIETY, Memphis, Tenn.