August. 1927
INDUSTRIAL A N D ENGINEERING CHEMISTRY
939
Studies of Chaulmoogra-Group Oils’ 11-With Special Reference to Refining and the Isolation of Hydnocarpic Acid2 By G. A. Perkins, A. 0. Cruz, and M. 0. Reyes CHEMICAL sBCTION, PHILIPPINE HEALTH SERVICE, LEPEi? COLONY, CULION, P. I.
E ARE frequently informed, in the scientific and of small amounts of some glucoside, vitamin, or other subsemi-scientific press, that the intramuscular and stance which would account for the activity supposed to subcutaneous injection of chaulmoogra. oil, begun be lost on refining. Such searches have been in vain. On in the nineteenth century as a treatment for leprosy, failed the contrary. the effectiveness of chaulmoogric and hydnobecause the oil is “heavy,” “slowly absorbed,” “very ir- carpic acids in the form of ethyl esters or sodium salts has ritating.” Nevertheless, intramuscular or subcutaneous been firmly established. Although the activity of the above-mentioned ethyl esters injection of chaulmoogra-group oils is a t present employed on a large scale for the treatment of lepers in various coun- and sodium salts is no longer doubted, the pure chaulmoogratries, and the local irritation produced by the treatment group oils, largely because they are considered less likely is not serious. The comparative failure of the earlier work, to produce untoward effects, have recently been preferred in so far as local irritation was involved, is ascribable to for the treatment of certain t m e s of cases. In 1921 we the fact that the oil used was learned that the Japanese6 of a very low grade. To had discovered the value of “chaulmoogra” (probably borrow an expressive phrase For more than twenty years investigators mixed from the language of the Hydnocarpus anthelmintica) chaulmoogra oil with various substances to make it law courts, it was “decomoil of low acidity, and were suitable for intramuscular or subcutaneous injection. using it by subcutaneous posed, rancid, putrid, and These mixtures have been practically abandoned, as it unfit for human consumpinjection. More recently is now known that chaulmoogra-group oils, if free from tion.” Hydnocarpus wightiana oil rancidity, are very suitable for use without admixture. of low acidity has come into (The term “mixtures” does not include such preparaAt that time, as at prestions as chaulmoogra ethyl esters, which are derived e x t e n s i v e use in India.’ e n t , t h r e e chaulmoograThis is not refined oil, but from the oil by chemical changes and have a distinct group oils were used for the cold-pressed oil from seeds place in leprosy therapy.) The most important part of t r e a t m e n t of leprosythe refining process is the removal of free fatty acids. of good quality. Seeds or Tnraktogenos kurzii (chaulThe details of refining are described. oil of H . anthelmintica and moogra), Hydnocarpus Hydnocarpus wightiana oil is more economical than H . wightiana, in contrast to wightiana ( m a r o t t i ) , a n d chaulmoogra, because obtainable in better quality. H. t h o s e of t h e true chaulHydnocarpus anthelmintica m o o g r a , can be obtained wightiana oil is also more suitable for the prepara(lukrabo). Unfortunately, commercially in excellent tion of hydnocarpic acid. By fractionation of the ethyl chaulmoogra was the only esters from this oil nearly pure ethyl hydnocarpate quality. one of these well known to can be obtained, whereas the corresponding fraction occidental physicians. Rancidity is now recogfrom chaulmoogra ethyl esters is contaminated with Chaulmoogra s e e d s a r e nized as highly detrimental, ethyl palmitate. Hydnocarpic acid was obtained in obtained from d a n g e r o u s but the prejudice against considerably better yields and purer condition than forests, and their collection refined oils, as compared previously reported. is usually deferred until the w i t h c r u d e oils of fairly Analytical characteristics of some chaulmoograbears have finished eating good quality, still exists. At ’ group oils of minor importance are recorded. t h e c h a u l m o o g r a fruit.3 C ul ion , however, refined The Taraktogenos seed does’ oils have been used for sevnot keep well, and “crude, eral gears. The physicians cold-pressed” commercial chaulmoogra oil contains 13 to 60 here have found that adequately refined chaulmoogra oii per cent of free fatty acid. is a satisfactory medicinal product (though less active than It was doubly unfortunate, and indeed surprising, that the ethyl esters). From a medicinal standpoint there appears the refining of this rancid oil, though recommended by to be no difference between this and refined Hydnocarpus Jean~elme,~ was looked upon with disfavor by practically wightiana oil. So little local irritation is produced by these all the physicians who treated lepers. Brill and Williams5 refined oils that the admixture of other ingredients to rewere not entirely convinced of the validity of the practi- duce the irritation has been abandoned as entirely unnecessary. tioners’ conclusions, but they were nevertheless strongly Crude H. wightiana oil is obtainable* commercially a t influenced by such conclusions and by faulty observations less than $1000 per ton with a much lower acidity than purporting that “the compound known as anti-leprol, which commercial chaulmoogra oil of the same or higher prices. is the mixture of the ethyl esters of chaulmoogric and hydno- For economical reasons, therefore, the H. wightiana oil carpic acids, was without effect.” Accordingly, they and rather than chaulmoogra is now being refined here. The other chemists examined crude chaulmoogra oil in search refining loss is considerable in the case of commercial chaulmoogra oil. This loss m a y be minimized, however, through 1 Received March 26, 1927. Published with the permission of the recovery, by acidification, of the fatty acids and oil present Director of Health upon recommendation by the Philippine Leprosy ReI -
search Board. * The first paper of this series was b y Perkins and Cruz, Philippine J . sci., as, 543 (1923). Rock, U. S. DcPI. Agr., Bull. 1011, 18 (1922). 4 Prcssc med., IS, No. 98,989 (1911). 6 Philippine J . Sci., 188, 207 (1917).
*
8
Mitsuda. IIIe Conference Internationale de la Lepre, Paris, 1924, p.
7
Muir, Leprosy-Diagnosis,
263. Treatment, and Prevention, Cuttack,
p. 9 (1925). 8 The Ernakulam Trading Co., Ernakulam, India, appears to be the only large producer in the areas where this seed is grown.
940
INDUSTRIAL A N D ENGINEERING CHEMISTRY
in the soap solutions drawn off in the refining process. This fatty acid mixture may be utilized in the preparation of ethyl esters. The refining methods a t this laboratory are very simple, and undoubtedly could be improved by an experienced oil refiner. Difficulties have been reported by other workers, however, and as nothing appears to be available on the subject in the literature, these methods are being recorded here. Refining Technic
In order to remove volatile impurities, steam is passed through the oil for about an hour, either before or after washing with alkali. Sufficient steam is used to give an aqueous distillate of about one-fifth the volume of the oil. The amount of volatile impurities is very small, but the distillate has a strong odor. The free fatty acids are removed by washing with a solution of caustic alkali, the only difficulty being in the separation of the pure oil from the resulting emulsion. The essential points are believed to be as follows: 1-Heating is required for the separation of the emulsion; in the cold, considerable solid sodium acid chaulmoograte is formed. The better grades of crude oil require only that the water be hot a t the start; the lower grades require a temperature of about 90’ C . for several hours a t each settling. 2-If much soap is present the stirring must be gentle, or a fine, inseparable emulsion will be formed. 3-The original emulsion separates into a fairly clear lower layer and a thick, creamy upper layer, which still contains a considerable portion of the soap. 4-Long heating of this creamy layer with water t o remove the soap results in the formation of free fatty acids in the oil. If not much soap is present hot water may be added and the whole allowed to cool and settle. If much soap is present, hot dilute alkali is added and the temperature maintained for several hours. Addition of cold, dilute alkali, with subsequent heating, usually results in much less rapid settling. 5-When sufficient soap has been removed, the oil separates from the emulsion. Addition of salt hastens the separation, but the oil so obtained contains most of the soap. Therefore, the addition of salt is not advisable until sufficient soap has been removed so that separation of the oil has already begun. Experimental R u n s
H. WIGHTIANAOIL (2.5 per cent acidity)-One hundred and fifty liters of hot water (about 80” C.) were run into a 400-liter steel drum provided with a faucet a t the bottom; 0.5 kg. of lye (74 per cent NaOH) was added, and then 100 liters of H. wightiana oil were thoroughly miked in. After the emulsion had stood 24 hours the clear lower layer (about 125 liters) was drawn off. Hot water was run in, with stirring, up to the 350-liter mark. After 2 days the slightly opalescent lower layer (200 liters) was drawn off. The washing with water was repeated four more times, with settling each time until the lower layer cleared, 24 hours usually being sufficient. Ninety-five liters of oil were obtained, with a n acidity of 0.2 per cent. This oil was steamed as described above and filtered, while hot, through folded ‘filters. The filtrate was dried by heating in an enamel-ware kettle, filtered again, and sterilized in bottles a t 150° C. CHAULMOOGRA OIL (25.5 per cent acidity)-In an open, copper, steam-jacketed kettle 20 liters of chaulmoogra oil and 30 liters of water were heated to boiling. A solution of 1.02 kg. of lye (74 per cent NaOH) in 5 liters of water, calculated to be about 10 per cent in excess, waa stirred in. The mixture was kept hot (about 95” C.) for 5 hours. The nearly clear soap solution (about 35 liters) was drawn off. A hot solution of 200 grams of lye in 35 liters of water was stirred in, and the mixture kept hot overnight. The clear lower layer (abmt 37 liters) was drawn off.
VOl. 19, No. 8
A hot solution of 100 grams lye in 32 liters of water was stirred in, and the mixture kept hot for 7 hours. The slightly milky lower layer (34 liters) was drawn off. A little clear oil was noted on top, but most of the oil was in a creamy emulsion. This was broken by the addition of 100 grams of salt, which produced a lower aqueous layer of about 3 liters and an upper layer of oil containing a little water and soap. The contents of the kettle were transferred to an open pail and heated by an atmocphere of direct steam for several hours. The small amount of soap was removed by filtering twice while warm, the aqueous solution being separated after the first filtration. A final filtration in the cold gave a clear product; yield 10.4 liters, acidity 0.28 per cent. In using this method steaming may be done first or after the first filtration. Hydnocarpic Acid
One of the objects of the earlier paper2 was the evaluation of various oils as potential sources of chaulmoogric, hydnocarpic, or other acids which might be found valuable. Chaulmoogric acid is readily obtained from any of the chaulmoogragroup oils (especially Hydnocarpus alcalae), but this acid, in pure form, has found no extensive therapeutic application. Hydnocarpic acid is not so readily obtainable. Recently sodium hydnocarpate has been required in this colony for clinical investigations. Hydnocarpic acid was originally obtained by Power and Barrowcliffgfrom Hydnocarpus wightiana and other oils by fractional crystallization of the barium salts. Dean and Wrenshall’O fractionally distilled the fatty acids of chaulmoogra oil and recrystallized the lower boiling fractions. By a large number of fractional crystallizations they obtained about 50 grams of hydnocarpic acid from a kilogram of low-grade oil and better yields from oil of higher grade. Sacks and Adams,l1 using a similar method but only five crystallizations, obtained about 20 grams per kilogram of chaulmoogra oil. Ghosh12 crystallized the fatty acids from a number of oils and obtained fractions melting at 60” C., or somewhat less, which he called hydnocarpic acid. Fractions melting a t above 50” C. gave sodium salts which were foundI3 to be suitable for therapeutic use, and a medicinal product made in this way is sold by a Calcutta 6rm as “sodium hydnocarpate.” Since crystallization of the chaulmoogra or hydnocarpus fatty acids does not produce hydnocarpic acid, and since fractions made in the manner described are obviously mixtures and yield chaulmoogric acid on further crystallization, the names “hydnocarpic acid” and “sodium hydnocarpate” should not be applied to these products. The most practicable way to isolate hydnocarpic acid seems to be by distillation followed by crystallization. T h e writers preferred to distil the ethyl esters rather than the fatty acids, because the former are more easily made in fairly large quantities than the latter, provided one has a constant steam supply, they are more stable, and much more easily distilled. Dean and Wrenshall, distilling the fatty acids or the ethyl esters a t 1 to 4 mm., had difficulty in controlling the fractionation by temperature, owing to slight fluctuations in pressure, and eventually used a single fractionation of the fatty acids, controlled only by volume. Since there seems to be no advantage in such low pressures, at least for the ethyl esters, the present writers used an adjustable mercury trap to hold the pressure a t 20 mm. The column J . Chem. SOC.(London), 87, 884 (1905). J . A m . Chcm. Soc., 49, 2626 (1920). 11 Ibid., 48, 2395 (1926). 1 2 Indian J . Med. Research, 8, 211 (1920). 1 3 Rogers, Indian Med. Gaz., 64, 165 (1919). 9
10
August, 1927
INDUSTRIAL AND ENGINEERING CHEMISTRY
was not so long as would be desirable, but by three or four fractionations it was possible to concentrate most of the ethyl hydnocarpate in a 4" C. fraction (210-214" C.). Preparation of Hydnocarpic Acid Crude H . wightiana oil of good quality (2.5 per cent acidity)
was converted into ethyl esters by boiling with alcohol and sulfuric acid.14 The ester was washed with water and dried. A standard 3-liter, long-necked, round-bottom, Pyrex boiling flask was used for distillation. The neck was nearly filled with broken glass supported by an inverted cone of wire netting, which was hung from the cork. The cork was impregnated with glue and had two holes to accommodate the stillhead and an inlet tube for the introduction of portions. The inlet tube did not intrude beyond the cork, and was also used to drain off the residue by inverting the flask. The stillhead, or deplegmator, was a simple "distilling tube" 2 by 24 cm. with side arm but without constriction a t the bottom. Constricted distilling tubes did not allow sufficient flow-back. FIRSTDISTILLATIOX-TWOliters of ethyl esters were placed in the flask and two portions of 600 cc. each were collected. The remainder was discarded (or distilled for the preparation of chaulmoogric acid if desired). The flask was washed with alcohol, without removal of the main cork, each time the residue was drained off. The second 600-cc. portion was again placed in the flask with 1400 cc. of crude ethyl esters. Two 600-cc. portions were again distilled, the second of which was distilled with 1400 cc. more of crude ester. A final total of 1800 cc. of first fraction and 600 cc. of second fraction were thus obtained. SECONDDIsTILLaTIoN-These two fractions were refractionated, the second being added to the flask when the temperature rose to 217" C. Result: (I) 120-212" C., 450 CC., (11) 212-217" C., 1120 CC.;(111) 217-230' C., 590 CC. THIRDDISTILLATION-T~~ three fractions were redistilled Result: (I) 120-200" C., 40 cc.; (11) 200-212" C., 560 cc.; (111) 212-214" C., 890 CC.;(IV) 214-220' C., 410 CC.;(V) 220-230" C., 220 CC. A small portion of the 212-214' C. cut was saponified. The resulting fatty acid showed a freezing point (thermometer bulb immersed) of 52.5" C., and [a] ,:' 61.7". FOURTH DIsTILL.ITION-Result: (I) 120-200" c., 74 cc.; (11) 200-210" C., 252 cc.; (111) 210-212" C., 453 cc.; (IV)
+
212-214" C., 723 CC.; (V) 214-216' C., 178 CC.; (VI) 216220" C., 100 CC.;(VII) 220-230" C., 200 CC. Fractions I1 to V were saponified. The freezing points and [a13: of the fatty acids were as follows: (11) 51.4" C.. +57:4';- (111) 53.7' C., + 6 l . l " ; (IV) 53.8; C.,+62.3", (.1'), 51.4" C.. +62.5".
The melting points of the fatty acid fractions, by the usual capillary tube method, were about 2" C. higher than the above values, which were taken with the thermometer bulb immersed in the half-frozen liquid. Power and Barrowcliff record a melting point of 59-60" C., and [ a ]D, +6S.l", for pure hydnocarpic acid. It is evident that nearly pure ethyl hydnocarpate can be obtained from H . wightiana ethyl esters by fractional distillation alone. The purity had apparently not reached the maximum obtainable by distillation, but for the present purposes purification by recrystallization was started a t this point. RECRYSTALLIZATION-Fractions I11 and IV were combined and recrystallized six times from about 2 volumes of 80 per cent alcohol (with slow cooling each time to about 15" C.). The alcohol adhering to the final crystals was removed by mixing them with hot water. The fatty acid solidified in a cake on cooling, and the remaining water was removed by remelting. The product weighed 360 grams; 14
Perkins, Philrppine J. Sci., 24, 627 (1924).
94 1
freezing point, 58.2 O C.; melting point (in capillary tube) 60" C.; [a]?, f70.7" (20 per cent solution in alcohol; the rotation in chloroform was found to be the same). Fractions I1 and V, combined, were crystallized from each of the six mother liquors (from the above) in turn. Product: 343 grams; freezing point 57.8" C.; melting point 59.5" C.; [a]y , +69.7".
The six mother liquors were then separately treated with hot water. The six portions of fatty acids thus obtained had the following properties: PORTION
I
I1 I11 IV V VI
WEIGHT FREEZING POINT Grams c. 36 150 41 113 42 132 87 45 35
48 46 2 50 1
Degrees +45 +47 +49
+,54
+t54 57
These fractions from the mother liquors evidently contained considerable hydnocarpic acid, and were reserved for further crystallization in combination with other similar fractions. A basket centrifuge is better adapted than a porcelain funnel (used in the above) to the draining of the extremely fine crystals which impure fractions give, even on very slow crystallization. YmLDs-The ethyl esters used in the foregoing run were obtained from 4.7 kg. of oil. The two crops melting at 60" and 59.5" C., therefore, represent a yield of 150 grams per kilogram of oil. Apparently 25 to 30 per cent of the oil consists of hydnocarpic acid, and a large part of this can be isolated by sufficiently thorough fractionation. PRESERVATION OF HYDNOCARPIC ACID-Hydnocarpic acid is rapidly attacked by the air when left in loose crystals. When allowed to solidify after melting, however, it keeps quite well. Heating a thin layer in air for more than a few minutes to drive off solvent results in lowering of the melting point. LOWER BOILISG FRACTIOXS-POWer and Barrowcliff considered it probable that H . wightiana oil contains a lower homolog of hydnocarpic acid with fourteen carbon atoms. Dean and Wrenshall found in chaulmoogra oil no evidence of members of the chaulmoogric series below hydnocarpic acid. In the fourth distillation of H . wightiana ethyl esters recorded above it was found that only 74 cc. distilled below 200" C. By combining the low-boiling fractions from the distillation of about 100 liters of esters it was found that on refractionation most of this portion distilled above 200" C. No evidence was obtained of any appreciable quantity of CI4acid. but there was a definite concentration at 160-165" C. This fraction showed a specific rotation of about +16", unchanged by refractionation. The writers have not yet succeeded in isolating the substance responsible for the rot a tion. HYDNOCARPIC A C I D FROM CHAULMOOGR.4 OIL-POWer and Gornall15 found in chaulmoogra oil a considerable quantity of palmitic acid, One would therefore expect the ethyl hydnocarpate fraction from this oil to be quite impure. This was found to be the case. On fractionating 5.4 liters of neutral ethyl esters from chaulmoogra oil three times, about the same yield of crude ethyl hydnocarpate fractions was obtained as from H . wightiana oil. The best of these fractions, however, gave on saponification fatty acid freezing f43.8". a t 42" C.; The oil used was a medium-grade commercial chaulmoogra oil of 25 per cent acidity. Unfortunately, no authentic crude samples of a better grade were on hand for comparison, to determine whether rancidity was partly responsible for the poor result. The results were no better, 15
J . Chem. SOC.( L o ~ z ~86, o ~846 ) , (1904).
942
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
however, when the oil was thoroughly refined before making the ethyl esters. A run was also made with a crude H . wightiana oil of 9.5 per cent acidity, hydnocarpic acid of freezingpoint 53.3O C. being obtained, by three distillations. It is therefore concluded that chaulmoogra oil is not suitable for the economical production of hydnocarpic acid. Analysis of Minor Oils
In continuation of the analysis of various chaulmoogragroup oils begun in the earlier paper12 examinations were made of the seeds of Asteriastigma macrocarpa (from the Conservator of Forests, Travancore, India), Hydnocarpus caulijora (from the Provincial Treasurer, Cotobato, P. I.), Hydnocarpus ovoidea (from W. A. V. Wiren, Catarman, Samar, P. I.), and Hydnocarpus woodii (from D. D. Wood, Conservator of Forests, British North Borneo). Table I shows the general characteristics of the oils obtained by extraction of these seeds. The Asteriastigma seeds are very similar in appearance to those of Hydnocarpus alcalae, and the high freezing point of the fatty acids of the former approaches that of the latter (55" C.). Fractionation of the ethyl esters gave further evidence of the similarity of these two oils, in that the first fraction from each gives chaulmoogric acid instead of hydnocarpic, on hydrolysis and recrystallization. The Asteriastigma oil is inferior to H . alcalae oil in rotatory power, however.
Vol. 19, No. 8
The seeds and oil of Hydnocarpus caulij7ora are very similar to those of H . hutchinsonii. The very low optical rotation of H . oviodea oil precludes its classification, chemically, as a chaulmoogra-group oil. The data for H . woodii are somewhat different from those reported in the earlier paper for a small and rather old sample. On fractionating the ethyl esters from this oil it was found to be very similar to the oil of T. kurzii. T a b l e I-Characteristics Asteriasligma OIL macrocarpa Sp. gr., 3Oo/3O0 C. 0.936 n3: 1.4709 Freezing point, O C. 30 Rotation 100 mm., 36 Iodine number, Hanus 87.6, Saponification number 201 Acidity, as per cent oleic 8.2 Fatty acids: Freezing point, C. 50 39
of S o m e Minor Oils HydnoHydnccarpus carpus cauliflora ovoidea 0.946 0.915 1.4732 1.4637 25 25 42 1 84 47 201 215 0.8 5.8 42 38
40 0.7
Hydno: carpus woodii 0.949 1.4755 21 49 96 206 2.;
44 55
A sample of seeds obtained from a Calcutta firm as Hydnocarpus Castanea was examined, and the ethyl esters from it were fractionated. Data on this oil are not included in the table because the writers were not able positively to identify it botanically and because the oil was found indistinguishable chemically from that of T. kurzii.
Repellents for Blowflies' By R. C. Roark,*D. C. Parman, F. C. Bishopp, and E. W. Laakes BUREAUOF C H E ~ S T RAND Y BUREAUOF ENTOMOLOGY, WASHINGTON, D. C.
B
LOWFLIES are true flies that deposit their eggs or larvae on meat or in wounds on living animals or man. The larvae feed on the tissues of their host and usually cause death within a few days unless remedial measures are taken. There are many genera of blowflies, such as CaZZiphora, Lucilia, Sarcophaga, Cochliomyia, etc. One species of the lastnamed genus, C. macellaria Fab., is known in the United States as the screw-worm fly, and is estimated to cause an annual loss of at least $4,000,000 to the livestock owners in the southwestern states. In Australia and other wool-producing countries great loss among sheep is caused by Lucilia and Calliphora. The study of materials which may be used to kill blowfly maggots in wounds on animals, or to repel the flies, or to prevent their ovipositing in the wounds, is therefore one of great economic importance. Previous Work
Chloroform has been extensively used to kill maggots in wounds, but benzene has been found by Parman4to be more suitable and is now generally used in this country. For use as a repellent, nearly every material with a strong or disagreeable odor has been suggested at one time or another. Such materials as pyridine, fish oil, bone oil, and various essential oils have been proposed for this use by many authors in the agricultural literature. Proprietary preparations sold Part of paper presented by Mr. Roark before the Division of Agricultural and Food Chemistry a t the 73rd Meeting of the American Chemical Society, Richmond, Va., April 11 to 16, 1927. Insecticide and Fungicide Laboratory, Miscellaneous Division, Bureau of Chemistry. a Investigations of Insects Affecting the Health of Animals, Bureau of Entomology. 4 J. Agr. Research, 51, 885 (1925). 1
*
as screw-worm fly repellents usually contain crude carbolic acid, which is effective in keeping the flies away from wounds on which it is applied but the lower phenols are very toxic to cattle and other animals, and death of the host often results from the use of these preparations. Investigations conducted by the Bureaus of Entomology and Chemistry N u m b e r of Screw-Worm Flies C. macellaria Fab. Observed Visiting Fresh Beef Liver Treated w i t h v a r i o u s R e p e l l e n t s bornpared w i t h t h e N u m b e r Observed Visiting U n t r e a t e d Fresh Beef Liver (Figures are totals of several tests made at different times.) REPELLENT APPLIED~ DILUTED U N D I L u TE D PerPerNumber centage Number centage ratio ratio ratio ratio Powders: 3:324 1 1 :966 0.1 Copper carbonate 50 :862 6 Pyrethrum powder 14:231 D 71:1502 9:87 10 Powdered fresh cloves 76:1116 7 37:319 12 Iodoform 20 1:366 0.3 553276 Pinene hydrochloride 57 :260 0:770 0 22 Chloroacetophenone 15: 154 10 145:329 44 Hexachloroethane 53:199 27 5 5 : 101 54 Black pepper 212:929 23 133:232 57 Naphthalene 5 30:634 216:350 62 Derris powder Liquids: Wood naphtha Pine oil No. 4 Clove oil Turnentine. crude Chloropicrin Pine tar oil (sp. gr. 1.065) Pine tar Cade -~~~oil ~~. Ceylon citronella oil Star anise oil Pyridine Guaiacol American pennyroyal oil &Naphthyl, ethyl etherb Bergamot oil ~
26:296
240: 1635 422 : 1599
783286 599:1822 553: 1568 59: 160 519: 1366 259:455 787: 1366 192:312 841 : 1366 101: 160 1066: 1366 565:293
9 15
26
26 33 35 37 38 57 58 62 62 63 78 193
a Materials are arramed in the order of decreasina effectiveness as repellents when diluted. b Impure material which was liquid at the temperature of the tests.
