1426
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
in the guaiacol test by strong color development after 3 to 5 miriutes. Iri contrast to snap beans, the ascorbic acid of peas was complrtely retained in both packs during 1year at 0 O F. At 10 a or a t 0" to 20" F. the peas lost approximately half of the vitamin in 12 moriths. Although no carotene determinations were made on the samples entering experimental storage, duplicate samples of the 1945-pack peas after storage for 12 months showed average carotene contents of 20.5, 20.2, and 19.8 micrograms per gram a t O o , lo", and 0" to 20" F., respectively. Hence the temperature coefficient for destruction of carotene in frozen peas must he very low. DISCUS SIVN
The many striking changes in quality of the four frozen foods during storage appear to be attributable to exposure t o tempeiatures above 0" F. The rancidification of pork, the loss of' ascorbic acid from strawberTies, beans, and peas, and the drop in palatability of all these items (except the peas of the 1944 pack) when subjected t o frequent cycling of the temperature between 0' and 20" F. were qualitatively and quantitatively similar t o the changes observed Then the storage temperature v( RS held a t 10O F. After completion of this study, a paper by Woodroof and Shelor ( t 1) indicated that strawberries deteriorated more rapidly at a temperature fluctuating from 0' to 10 F. than when held constant at 10" F. The nature of the cycle of temperature fluctuation was not further defined. A possible explanation of their contradictory findings on stranberries is that no sirup or sugar was added as it interfered with tenderometer and leakage rxperiments (used as criteria of quality). Presence of the usual sugar sirups should afforda stabilizing influence. These data suggest that with the possible exception of et desiccating effect, temperature fluctuation, as such, does not seriously impair t,he qualitv of frozen foods. These findings confirm and
Vol. 40, No. 8
extend the observations of Hustrulid and Winter (4)in this respect. Before broad generalizations can be drawn, however, further studies on additional products should be made. These results again emphasize the importance of maintaining storage temperatures at 0" F. or lower if the eating qualities and nutritional values of frozen foods are to be maintained from season to season. A c m 0 WL EUGMEM
The authors wish to thank the Sears, Roebuck Company, Chicago, Ill., and the Jewett Refrigerator Company, Buffalo, X. Y., for their cooperation in providing freezer cabinets and Birds Eye-Snider, Inc., Albion, N. Y., for the frozen strawberries, beans, and peas used in this study. Acknowledgment is made to Marjorie Swisher, formerly of the staff of the Bureau of Human Nutrition and Home Economics, for some of the analyses reported here. L I T EKATU K h CITE I)
(1) Christensen, P. B., Food P"reezzng, 1, 25 (1945). (2) DuBois, C.W., and Colvin, D. L., Fruit Prod. J . , 25, 101 (1945) (3) Guest, W. E., Ice and Refrig., 96,339 (1939). (4) Hustrulid, A.,and Winter, J. D., Agr. Eng., 24,416 (1943). (5) Kokatnur, TI. R., and Jelling, M., .J. Am. Chem. Soc., 63, 1439 (1941). (6) Masure, M. P., and Campbell, H., Fruit Prod. J., 23,369 (1944) (7) Nelson, W.L.,and Somers, G. F., IND. ENG.CHEM.,ANAL ED., 17,754(1945). (8) Research Corp. Committee, Cereal Chemists Bull.. 2 (May 1942). (9) ShreGsbury, C. L., Horne, L. W., Braun, W. Q., .Joldan, R., Milligan, O., Vestal, C. M., and Weitkamp, N. E., P?rrdue Agr. E x p t . Xta. B u l l . 472 (1942). (10) Woodroof, J. G., Ga. Agr. Ezpt. Sta. B u l l . 201 (1938). ill) Woodroof, J. G.,and Shelor, E., Food Freezing, 2,206 (1947) RECEIVEDMarch 7, 1947. Work was'gerformed in cooperation wlth the Bureau of Human Nutrition and Home Economics, United States Department of Agriculture
'OPPER 8- UINOLINOLATE INDUSTRIAL PRESERVATIVE Y . G. BENIGNUS 4lonsanto Chemical Company, S t . Louis, iMo.
c
70PPER 8-quinolinulate i s the copper derivative of 8-quino-
linol which was prepared in 1880 by Bedall and Fischer (8) From quinoline sulfonic acid by fusion with sodium acetate and subsequent hydrolysis of the fusion mass. During this same year, Skraup (6) described a preferred method for preparing 8quinolinol, using o-nitrophenol, o-aminophenol, glycerol, and sulfuric acid; this reaction became well known as the Skraup synthesis. Although 8-quinolinol and numerous derivatives have been used for many years as pharmaceutical agents, the commercial manufacture and use of the copper derivative are recent developments as a result of the urgent need for a superior preservative for military fabrics during the recent war. . * Copper naphthenate, copper hydroxynaphthenate, copper oleate, copper stearate, copper ammonium fluoride, pemtachlorophenol, 2-chloro-o-phenylphenol, 2,2'-dihydroxy-5, 5'-dichlorodiphenylmethane, tetrabromo-o-cresol, 2,3-dichloro-l, 4-naphthoquinone, organo-mercuric compounds, salicylanilide, zinc dimethyldithiocarbamate, and various quaternary ammonium compounds were studied and used in connection with this program but none completely met the over-all requirements.
PHYSICAL AND CHEMICAL PROPERTIES OF COPPER 8-QUXfiOLINOCATE
Structural Formula :
H H
H H
I
H
/
H
Molecular 'Vl'eiglit = 351.83 Copper 8-quinolinolate, a light yellowish-green, odorless powder, is a practically nonionizable, chelated compound. Its copper is bonded firmly by both primary and secondary valence linkages, making the chemical very stable. It is quantitatively insoluble in acid or alkali within the p H range of 2.7 to above 12
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
August 1948
Manufacture and use of copper 8-quinolinolate as an industrial preservative is a new development arising from wartime needs for a superior preservative for fabrics. The chemical, physical, biological, and physiologicalproperties of copper 8-quinolinolate are described. These properties make the material especially attractive for preventing microorganism attack of cellulosic and proteinaceouscommodities where freedom from toxicity to humans is a requisite. Use of copper 8-quinolinolate as a preservative for fabrics is described. This fungistat is valuable also as a preservative for leather, wood, plastics, and many types of protective coatings.
1427
TABLE111. MINIMUM PROTECTIVE CONCENTRATIONS 70of Copper 8- uinolinolate
Based on $eight of Organisms" Treated Fabric Aspergillus niger 0.5 Chaetomium globosum 0 .1-0 .2 Myrothecium verrucaria 0.1-0.2 Penicillium sp. 0.1-0.2 a Quartermaster Corpa Tentative Specification (8) was followed for the Chaetomium and Myrotheczum test. Army Engineer Corps Specification (7) was followed for the Asperoillus nioer and Penicillinm tests.
TABLEIV.
FABRICS TREATED WITH COPPHR ~-QUINOLINOLATE FOR SOILBURIAL STUDIES ConnPr
8IQ;riO-
and its water solubility is 0.8 part per million a t 25" C. It is practically insoluble in common organic solvents. Its vapgr pressure and volatility are nil; the product is stable a t relatively high temperatures (400' F.), and it does not appear t o be affected by ultraviolet OF other actinic rays. DERMATOLOGY AND TOXICOLOGY
Particularly in the Preservation of fabrics and other commodities which come in contact with the skin, the dermatology and toxicology of copper 8-quinolinolate are important considerations. Patch tests have been made on 200 individuals according to the procedure recommended by Schwartz and Peck (6). The patch material was 8.25-ounce duck treated with copper 8-quinolinolate by immersing in a 3% aqueous solution of 8-qumolinol as acetate followed lay dipping in a 2% aqueous solution of normal copper acetate, rinsing with water, and drying. This investigation showed that copper 8-quinolinolate is not a primary skin irritant nor is it a sensitizer. These findings were confirmed by the experiences during the past year of operators engaged in the manufacture, formulation, and application of the product. Experimental toxicological studies (4) showed the toxicity of copper €4-quinolinolate to the higher animals to be of an extremely low order. The minimum lethal single dose for rats, administered orally, was found t o be 10 grams per kg. of body weight. Moreover, when sublethal doses of l gram per kg. of body weight were given orally to rabbits on 2 or 3 days per week until 23 doses in all had been administered, no signs of intoxication appeared and no significant histological changes in body tissues could be discovered on examination after sacrificing the animals. Copper 8-quinolinolate is no! acceptable to the animal physiology but its oral toxicity is believed to be much lower than those of most of the chemicals used routinely today in modern industry.
OF COPPER 8-QUINOLINOLATE TO FUNGI AS TABLE I. TOXICITY DETERMINED BY MALT-AGAR-PETRI DISH TEST(3)
Organisms Penicillium s p . Aspergzllus nL.zger Aspergillua ustus Chaetomium globosum iMyrothecium verrucaria M e t a m h i d u n sp. Trichophyton interdigitale
Type
Copper 8-Quinolinolate. Weight % Inhibiting Killing concn. concn.
General mold General mold General mold Textile rotter Textile rotter Textile rotter Athletes foot fungus
0.001
* o
0.001
0:65 0.05 0.20
0.05 0.05
0.20 0.001 0.001
....
TABLE 11. COMPARATIVE FUNGICIDAL VALUES O F COPPER 8QUINOLINOLATE AND OTHERCHEMICALS (Malt-agar-Petri dish test) Killing Concn. (Weight 70)for Chemicals Chaetomium globosum Aspergillus ustue Copper 8-quinolinolate 0.05 0.05 Co per pentachlorophenate 0.05 0.20 0.05 0.01 8-& uinolinol ' 0.01 0.1 Pyridyl mercuric acetate 0.01 Sodium pentachlorophenate
..
Sample Description B-5 Mineral dyed OD-7 JO cloth treated with copper-8 by one-bath water-in-mineralspirits process, followed by S/V Fabrisec M P water repellent SA-1 Vat dyed OD-7 Jo cloth treated with coup e r d b the two-bath aqueous process followeJ bv S/V Fabriseo M P water re: pellent AA-2 Mineral dyed OD-7 Jo cloth treated with copper-8 by the two-bath aqueous process, followed by S/V Fabrisec h l P water repellent
Copper,
%
linolate,
%
0.19
1.25
0.30
1.64
0.20
1.81
TOXICITY TO FUNGJ.
I n light of its relative freedom from toxicity to humans, it is interesting to note the pronounced toxicity of copper S-quinolinolate to lower forms of life. The toxicity of copper 8-quinolinolate to several types of fungi, commonly used in textile testing work, is given in Table I. In Table I1 are some comparative fungicidal values for this pregervative and other well known toxicants. These results show that the effectiveness of copper 8-quinolinolate against common' molds is comparable with the action of well known powerful fungicides, such as pentachlorophenol, its copper salt, and pyridyl mercuric acetate. COPPER 8-QUINOLINOLATE AS TEXTILE PRESERVATIVE
Probably the first industrial use for copper 8-quinolinolate was as a preservative for cotton fabrics. The minimum amounts of the preservative required to protect 8.25-ounce, desieed, cotton duck (gray goods) when inoculated with fungi in the presence of nutrients and incubated at optimum temperature and humidity are shown in Table 111. For the preservation of most commercial fabrics, about 1% of copper 8-quinolinolate based on the weight of the finished goods is recommended. This is about 2 to 10 times the minimum amount required to protect gray goods under laboratory testing conditions. Assurance of adequate protection thus is given even if the fabric is subjected to unusual weathering or to other un-, anticipated service conditions. PERMANENCE AND EFFECTIVENESS OF TREATMENT
When a plied to fabric in the presence of suitable bonding agents ancf'water repellents, copper 8-quinolinolate possesses an unusually high degree of permanence in the fabric. Samples of 8.25-ounce cotton fabric containing 1.201, of copper S-quinolinolate retain practically all of the preservative throughout 500 hours of leaching with running tap water, pH 9.0. Samples exposed to 6 months' weathering at et. Louis, Mo. (January to July 1944), suffered no measurable loss of preservative. Following these exposures, the preservative treated fabrics resisted attack of Chaetomium globosum, Myrothecium verrucaria, Penicillium sp., and Aspergillus niger when inoculated with these organisms in accordance with the test methods referred to in Table 111. Likewise, both the water-leached and weather-exposed treated fabrics resisted attack when inoculated with the mixed culture of organisms and a suspension of compoated soil as described (8). Cotton fabrics described in Table IV retain tensile strength as shown in Table V, when buried in composted soil. These tests
INDUSTRIAL AND ENGINEERING CHEMISTRY
1428
TABLEv-. RESULTS OF SOIL BURIAL TESTSO X DESCRIBED IS TABLE IV"
FaBRICS
-%
Changejn Tensile Strength bCopper 8-Quinolinolate Untreated Treated control, Sample Sample Sample mineral B-5 AS-1 AA-2 dyed OD 7
+
Burial: 7 days +2 0 4 - 65 14 days +3 -8 $3 - 80 Water-leached 24 hr., followed by burial 14 days 17 -7 $6 - 85 Water-leacded 72 hr., followed by burial: 4-7 -8 +4 14 days 4-6 0 +4 21 28 -2 -1 0 35 -3 t-2 +4 10 +1 42 +7 15 - 30 60 0 Burial, 14 days, after weathering: 0 0 +5 6 weeks -8 0 +3 3 months -2 6 months +4 +5 Soil burial test developed by the Jeffersonville, Ind., Quartermaster Depot. b Calculated on strength of treated sample before exposure.
+
+-
were made in collaboration with E. C. Bertolet at the Jeffersonville, Ind., Quartermaster Depot. E F F E C T O F ULTRAVIOLET L I G H T ON TREATED FABRIC
It is common knowledge that cotton loses tensile strength when exposed to ultraviolet light. Many chemicals studied and used as textile preservatives accelerate this reaction. Results given in Table VI indicate that copper 8-quinolinolate doas not accelerate the destructive action of ultraviolet light on cotton.
STRENGTH OF FABRIC EXPOSED TO TABLE VI. TENSILE ULTRaVIOLET LIGHT^ Yo Retention of Original Strength 8.25-02. gray goods treated q i t h , l % Untreated (gray Hours Exposed copper 8-quinolinolate goods) control 86.4 98.7 24 71.5 98.1 48 70.0 90.0 72 68.6 89.0 120 68.0 72.2 220 60.7 65.2 348 a Atlas Weatherometer Type BMC single arc machine operating with continuous light, but without water spray.
The results shown in Table VI are substantiated by the following test. Standard airplane cloth treated with 1% of copper 8-quinolinolate lost only 4.5y0 of its strength when exposed for 100 hours in a National Carbon arc weathering machine, equipped with Cordex D filters which cut off all radiation below 2700 Angstrom units t o correspond with natural sunlight. A similar untreated control sample lost 16.8% of its strength when exposed under similar conditions.
.
FIELD PERFORMANCE T E S T S MADE BY GOVERNMENT AGENCIES A T HARBEL, LIBERIA
.
Through arrangements made by C. C. Yeager of the Army Air Forces Materiel Command at Wright Field, the fabrics described in Table IV were tested, also, under various tropical exposure conditions at the Firestone Rubber Company Plantation, Harbel, Liberia. The severity of the climatic conditions prevailing in this area during the 6-month testing period is shown by the meteorological data given in Table VII. At one time during the month of August there was as much as 1.5 inches of rainfall in one hour. Ordinarily, for several hours of each day the relative humidity is 98 to 100%. Details of the
Vol. 40, No. 8
exposure tests at Harbel, Liberia, and the loss of tensile strength of the fabrics are given in Table VIII. FIELD STUDIES A T B A R R 0 COLORADO ISLAND, CANAL ZONE
Copper 8-quinolinolate-treated fabrics were included in tests sponsored by the National Defense Research Committee and supervised by Elso S. Barghoorn a t Barro Colorado Island, Canal Zone. The work %'as done for the Joint Army-Navy-NDRC Tropical Deterioration Steering Committee a t the request of the Office of the Quartermaster General; the results are reported in (1).
Results of this tropical field study indicate the compaiative preservative values of a number of fungicides including: copper naphthenate, copper hydrosynaphthenate, tetrabromo-o-cresol, phenyl mercuric triethanolamine lactate, 2,2'-dihydroxy-5,5'dichlorodiphenyl-methane, copper ammonium fluoride, trimethyloctadecylammonium pentachlorophenate, copper 8-quinolinolate, Permacide AM-IO (a phenyl mercury compound), pyridyl mercuric chloride, pyridyl mercuric stearate, phenyl mercury phenolate, and the phenyl mercury salt of 2-mercaptobenaothiaxole. The copper 8-quinolinolate-treated fabric used for the test was 9.5-ounce, Oxford, olive drab No. 7, shelter-tent duck which was finished with an aluminum acetate-wax-type water repellent. The finished fabric contained about 1.5% of copper 8-quinolinolate and a total copper content of 0.31% by weight. EXPOSURE TO SUNLIGHT. The copper 8-quinolinolate-treated fabrics exposed for 16 weeks in the sun-exposure plot showed a loss of 43% in tensile strength. Under similar conditions the untreated control lost 42%. There was no mildew visible on either the treated sample or the control. Results of this test indicate that the copper 8-quinolinolate treatment does not accelerate degradation of the fabric by actinic action. EXPOSURE TO DEEP SHADE. There was no loss of tensile strength of the copper 8-quinolinolate-treated fabrics exposed for 12 weeks in the shade whereas a comparable, untreated fabric lost 17% of its strength. GROUNDCONTACT.After ground contact for 7 weeks the copper 8-quinolinolate-treated fabric had not lost tensile strength; the control fabric lost 52% of its strength. SOILBURIAL. Under the more drastic conditione of soil burial the treated fabric did not lose tensile strength after 4 weeks'
TABLEVII.
METEOROLOGICAL DATAFOR EXPOSURE PERIOD (1946) HARBEL, LIBERIA
Mean max. temp. Mean min. temp. Av. of max. and min. means Highest max. temp. Lowest min. temp. Lowest max. temp. Highest min. temp. Hours sunshine Days rainfall Inches rainfall
TABLEVIII.
June 83.1 71.3 77.2 88.0 68.0 78.5 74.0 65.1 22 14.52
July 79.6 70.0 74.8 83 0 65.0 77 0 72.5 34.0 21 9.89
Aug. Sept. 7 9 . 8 82.1 70.0 7 1 . 3 74.9 76.7 84.5 87 . O 64.5 6 9 . 0 75.0 77.0 7 2 . 5 74.0 20.7 20.7 27 26 16.7 24.37
Oct. 84.3 70.8 77.6 89 .o 67.5 77.0 73.0 68.7 26 21.89
Sov. 87.4 70.9 79.1 89.0 67.5 83.0 73.5 122.0 17 5.42
TROPICAL FIELDEXPOSURE TESTSAT HARBEL, LIBERIA
Loss of Tensile Strength, % Exposure Conditions Untreated for 6 Monthsa control B-5 AA-1 AA-2 Exposed on elevated rack in open grassy plot to direct rays of the Bun; slope of panels just enou h to permit 68.6 34.4 48.6 29.4 run-off of rain water an2 dew Exposed on elevated rack in deep shade in secondary bush; slope of panels about 45' 89.9 9.1 4.3 4.9 Exposed on elevated rack under rubber trees where there was intermittent ,. 13.0 . sunlight 54.9 Exposed on the ground under rubber 100.0 31.7 . trees After 1 month of exposure, all control fabrios. were heavily attacked by fungi. treated samples appeared free from organlsm growth after exposure for 6 'months.
..
. .
August 1948
1429
INDUSTRIAL AND ENGINEERING CHEMISTRY
burial. After an extended burial Defiod of 13 weeks. the fabric lost only 31% of its strength. Under similar conditions of burial, the control lost 73 and loo%, respectively, of its initial strength.
ton. D. C.. and John D. Fleming of Monsanto Chemical Compa& for siggestions relative to preparation of the manuscript. LITERATURE CITED
Results of the tests show that copper 8-quinolinolate-treated fabric gave excellent field performance in every respect.
Barghoorn, E. S., Natl. Research Council (U.S.), OSRD Rept. 4807,April 1945; Textile Series,Rept. 24 (1946).’ Bedall, K., and Fischer, O.,Ber., 14,2570 (1881) Hunt, G. M., and Garrath, G . A., “Wood Preservation,” pp. 94-5, New York, McGraw-Hill Book Co., 1938. Kehoe, R. A.,personal communications regarding toxicology of copper 8-quinolinolate. Schwartz, L.,and Peck, S. M., U.S. Pub. Health Repts., 59,546I
ACKNOWLEDGMENT
The author is indebted t o the Institute of Paper Chemistry, Appleton, Wis., and to D. F. Rogers of Monsanto Chemical Company for some of the biological data reported. Acknowledgment is made to Elmer C. Bertolet and Allan McQuade, Jr., both formerly of the Jeffersonville, Ind., Quartermaster Depot, for the soil burial studies. The author wishes to express his gratitude to Glenn A. Greathouse and C. J. Wessel of the Prevention of Deterioration Center, National Research Council, Washing-
57 (1944). ’ Skraup, H.,Be?., 13, 2086 (1880). U. S. Army Engineer Corps Specification T-l212C., Sept. 12, 1943. U.S. Quartermaster Corps Tentative Specification 4471, Philadelphia Quartermasters Depot, Jan. 19, 1945. R~~~~~~~june 18, 1947.
ProDerties of Monomeric and Polvmeric 1 Alkvl Acrvlates and Methacrylates J
J
J
J
C. E. REHBERG AND C. H. FISHER Eastern Regional Research Laboratory, Philadelphia 18, Pa. T h e preparation and certain physical properties of various alkyl methacrylates, particularly the n-alkyl esters, are described. The curve obtained by plotting brittle points of the polymeric n-alkyl methacrylates against carbon atoms in the alkyl group is similar in shape to the corresponding curve of the n-alkyl acrylates. The brittle points of the n-alkyl polymethacrylates decrease with increasing molecular weight to the dodecyl ester (brittle point, -34‘ C.) and then increase. Cetyl polymethacrylate, the highest alkyl ester studied, had a brittle point of 15 O C. The brittle points of the first eight n-alkyl polyacrylates and twelve n-alkyl polymethacry-
I
N PREVIOUS papers ( I i , I 9 ) the preparation of various alkyl acrylates by a convenient method was described, and certain
properties of the monomeric and polymeric acrylic esters were reported. This paper contains additional data obtained in a more recent study of acrylic and methacrylic esters. Not all the n-alkyl esters were prepared, but from relationships observed between physical properties and molecular weights the properties of the missing members can be estimated. It is believed that the information reported herein is of value because of the growing importance of acrylates and methacrylates and the fact that earlier data on the subject, usually reported in patent literature, are either inadequate or unreliable. MONOMERIC ESTERS
Alcoholysis, a method previously employed (9, 6, 7, 11, 19, 16) in the preparation of both acrylic and methacrylic esters, was used in most instances in this work to make the higher alkyl acrylates and methacrylates. n-Tetradecyl methacrylate was made from methacrylic anhydride and the alcohol. The boiling points of *alkyl acrylates and methacrylates a t different pressures are given in Figures 1 and 2. The boiling points a t 10 and 760 mm. may be calculated from the total number of carbon’aboms, x, by Fquations 1to 4 (T = O K.).
lates are straight-line functions of the logarithm of the carbon atoms in the alkyl groups. Williams plastometer values of the polymeric n-alkyl acrylates, used as a measure of hardness, decreased with increasing molecular weight to approximately the nonyl ester. The plastometer values were proportional to the brittle points for the methyl to nonyl acrylates. Williams plastometer values obtained with the polymers of n-butyl, n-amyl, n-octyl, and ndecyl polymethacrylates decreased with increase in the length of the alkyl groups. The plastometer values of these polymeric methacrylates were found to be proportional to the brittle points.
n-Alkyl acrylates a t 10 mm a t 760 mm: n-Alkyl methacrylates at 10 mm. a t 760 mm.
T* 10-4
--
= 1.16 x
T2 10-4 = 1.87x 1.11 x TZ 10-4 TS 10-4 1.84 x
1.30 +++ 41.50 .40 + 4.20
$1(3) (4j
This method for relating boiling points a t 760 mm. to number of carbon atoms hzs been used previously ( I ,4,8). This relationship and those represented by other equations of this paper are usually unsatisfactory for the first two or three members of a homologous series. The boiling points ( O C.) a t 760 mm. of the n-alkyl acrylates and methacrylates, BE, can be estimated also from the boiling points of the corresponding alcohols, BA, by Equations 5 and 6 (Figure 3) :
+ 18 Methacrylates BE = 1.02 B A + 41 Acrylates B E = 1.07 B A
(5)
(6) The boiling points a t 760 mm. of the n-alkanols may be calculated (2’ = O K., z = carbon atoms):
T2
= 1.68 x
+ 8.50
With the exception of the first two members of the homologous series, straight lines were obtained by plotting refractive indexes of n-alkyl butyrates (3, 9, IS) against those of the corresponding alkyl acrylates and methacrylates (Figure 4 and Table I).
