PERKIN : QUERCETAGETIN. 209

XXI V .- Quercetagetin.

By ARTHUR GEORGE PERKIN.

QUERCETAGETIN was isolated from the flowers of the African marigold, Tugetes patula, by Latour and Magnier De La Source (Bull. SOC. chim., 1877, [ii], 28, 337), who state that it also occurs in other varieties of the same plant. I n appearance and general properties it is described as resembling quercetin, the colouring matter of quercitron bark, and from this fact, together with its origin, the name quercetugetin is evidently derived. On the other hand, according to these authors, its crystalline form, solubility in 60 per cent. alcohol, and the numbers obtained on analysis (C = 58-50 ; H = 3.97) indicated that it was distinct from quercetin, C27H20012, apd it was considered to pdssess the formula C,,H,O,, (anhydrous), or ~27H,0,3,4H20 (air-dried), I n order to isolate the colouring matter from the flowers, boiling 85 per cent. alcohol

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210 P%HKIN : QUEKCETAGETIN.

was employed, and the deposit, which separated by partly evaporating the liquid, was freed from plant wax and other impurities by extraction with chloroform or carbon disulphide. The crude substance, dissolved in alcohol, was precipitated by water and crystallised from dilute alcohol. Some years ago my attention was directed t o the subject by the late Prof. J. J. Hummel, who found that the flowers possessed well-defined tinctorial pro- pertiej, and a preliminary examination was then carried out (see P., 1902, 18, 75). As attempts t o obtain an adequate supply of the flowers were not successful, the work was abandoned for a time, and it is only recently, owing t o the kindneas of Mr. T. H. Burkill, Reporter on Economic Products to the Govern- ment of India, and t o Mr. D. Hooper, the Officiating Reporter, t o whom I am indebted for several pounds of the petals, that a more complete investigation has been possible. The method adopted for the preparation of the quercetagetin has differed considerably from that employed by its discoverers, it having been recognised that the main quantity of the substance was not present in the free condition in the material, but as glucoside. On the other hand, for purposes of economy, no attempt was made to isolate the glucoside in the pure condition, this being reserved for subsequent investigation.

EXPERIMENTAL.

The petals (1000 grams) were extracted for four hours with ten times their weight of alcohol, the extract evaporated to a small bulk, and poured into water, which caused the separation of viscous matter, possessing an aromatic’ odour. This was removed by shaking with ether ( A ) , the brownish-yellow aqueous liquid diluted with water to 3500 c.c., and heated to boiling with the addition of 125 C.C. of 33 per cent. hydrochloric acid. On keeping, a small amount of yellow, crystalline substance usually separated, but as the main bulk of the desired compound remained dissolved, thia could only be isolated by the tiresome operation of repeated extraction with much ether. After evaporation of the ether, a semi-crystalline, yellow residue remained, and this, by treatment with boiling water and keeping overnight, gave 17.2 grams of very crude colouring matter. It appeared evident from the method of isolation employed by Latour and Magnier De La Source that their product pre-existed in the flowers, for their operations did not involve the hydrolysis of a glucoside, and it was thus to be anticipated that some quantity of the substance was present in the ethereal extract ( A ) . This proved to be the case, for by shaking the ether with dilyte sodium carbonate solution, a yellow

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PEHKlN : QUERCE I'AGE'I'IK. 21 1

liquid was produced, which, when neutralised, gave a precipitate of 4.75 grams of the impure mat.eria1. To expedite matters, a t a later period some quantity of an alcoholic extract of the petals was very kindly prepared by Messrs, Hirst, Brooke, and Hirst, of Leeds, and in operating with this product it was stirred with boiling water, and the viscid, insoluble matter removed by decantation or by filtering through calico. The hydrolysis with hydrochloric acid was carried out a t a much greater concentration than that given above, in the expectation that the colouring matter would now be deposited in bulk on cooling, so that the ether treatment could be avoided, but this hope was not realised.

For purification the crude colouring matter from 1000 grams of the petals (22 grams approx) was treated with 130 C.C. of hot alcohol, filtered from a trace of a sparingly soluble substance ( B ) , the filtrate diluted with 90 C.C. of boiling water, and the crystals which had separated overnight were collected and washed with dilute alcohol. The yield was 13'2 grams, or 1.3 per cent., from the petals, and could not be materially increased by working up the filtrate, as this mainly contained a resinous impurity. By recrystallisation from dilute alcohol, the product was now sufficiently pure for most purposes, but for complete purification it was necessary to prepare the acetyl derivative, and after recrystallisation to hydrolyse this with hydrochloric acid in the usual manner. Traces of a substance which formed a more soluble acetyl com- pound were thus removed, but a loss of some 25 per cent. of material hereby occurred. For analysis, the colouring matter was dried at 160O:

-

Found, C = 56-64, 56-47 ; €€ = 3-46, 3-31.

As deposited from dilute acetic acid or dilute alcohol, it contains water of crystallisation :

Found, H,O = 10.10. C,,H1,O8,2H,O requires H,O = 10.16 per cent.

Quercetagetin forms pale yellow, glistening ' needles or leaflets, closely resembling quercetin in appearance, readily soluble in hot alcohol, and very sparingly so in boiling water. It melts a t about 318O, but owing to the darkening of the tube i t was difficult to be certain to one degree. Very dilute alkali dissolves i t with a pure yellow colour, which by air-oxidation becomes olive, and finally deep brown, but these changes are not so marked when a stronger alkali (10 per cent.) is amployed. Alcoholic ferric chloride

* The analyses given by Latour and Magnier De La Sourcc (Zuc. cit.) intlic,ate that their substance contained either a second colouring nmtter or wriic <Jther impurity of higher c:wIIon coikteut.

*C15Hlo08 requires C = 56.60 ; H = 3-14 per cent.

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21 2 PERKIN : QUERCETAGETIK.

produces an olive-green coloration, whereas cold alcoholic lead acetate forms an orange-red precipitate, which, on keeping, becomes yellower, and finally develops a green tint. The yellow potassium salt precipitated by alcoholic potassium hydroxide rapidly changes to green, and ultimately assumes a brownish-black colour. Quer- cetagetin does not contain a methoxy-group, and beyond conversion into the hydriodide is unaltered by prolonged digestion with liydriodic acid.

Acetylquercetagetin is readily prepared by digestiiig quercetagetin with five times its weight of boiling acetic, anhydride to wliich a few drops of pyridine have been added, for one hour. The solutioii diluted with its own voluirie of alcohol, on keeping, deposits crystals, which are purified by recrystallisation from a mixture of alcohol and acetic acid. For analysis, the substance (1 gram approx.) in 16 C.C. of acetic acid was liydrolysed by gradual addition of hydrochloric acid (15 c.c.) a t the boiling point. Hot water was then added, and the crystals of quercetagetin, which separated on cooling, were collected, and dried a t 160° (Found, C,,H,,O,=55*61, 55.82. Cl,H,08(C2H30), requires C,,Hlo08 = 55.79 per cent.).

Acetylquercetagetin consists of colourless needles, very sparingly soluble in alcohol. It melts a t 209--211°, or slightly higher than was stated previously (203--205O, Zoc. cit.).

Qu erce tage t in Sulp h a t c .-Quercetagetin closely resembles in general properties the colouring matters of the flavone group, and readily yields crystalline oxonium compounds when treated with mineral acids in the presence of acetic acid. Of these, only the sulphate, which is deposited in fine orange-coloured needles, was submitted to analysis (Found, C = 43.28, 42.69 ; H = 3-29, 3-26. C,,H,,08,H2804 requires C =43*26 ; H = 2-88 per cent.). By treat- ment with water, it is converted into quercetagetin and sulphuric acid.

Monopotassium quercetagetin, C,,H,08K (Found, K = 10- 74), sepa.rates as an orange-yellow, semi-crystalline precipitate when potassium acetat.e is added to a solution of quercetagetin in hot cbsolute alcohol. It possesses the general characteristics of the monosubstituted flavonol salts, and is readily decomposed by boiling water wit 11 separation of querce t agetin.

Action of Fused Alkal is 0 t h Quercetagetiit.--Five grams of quercetagetin were heated with 50 grams of potassium hydroxide and a little water to 200--220° for half an hour. The product was dissolved in water, the solution neutralised with acid, repeatedly extracted with ether, the extract evaporated, and the dark-coloured viscous residue, wliich partly solidified on keeping, treated with a little water. When no further separation occurred, the crystals

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PERKIN : QUERCETAOETIN. 213

were collected, drained on a tile, and purified by recrystallisation from water. The colourless needles melted at 194-196@, and possessed the properties of protocatechuic acid.

From the mother liquors no definite phenolic conipound could be isolated, and a second alkali fusion a t a slightly lower tem- perature was also fruitless in this respect. As a result of the later experiments described below, there can, however, be no doubt that such a compound is in reality produced during some stage of the liydrolysis, but is subsequently decomposed, probably by oxidation. Although it appeared likely that a t a much lower temperature, with weaker alkali and exclusion of air, the desired result might be obtained, it has not been possible to spare sufficient of the rare material for this experiment.

Q I ( erce tage t in P e n tame th, y l E= ther, C21,H2008.-Quercetagetin (8 grams) dissolved in methyl alcohol (100 c.c.) was treated with excess of methyl iodiae (50 c.c.), the mixture boiled, and a solution of potassium hydroxide (16 grams) in methyl alcohol added, drop by drop, during fourteen hours, this procedure being adopted as in the case of myricetin (T., 1902, 81., 245) with the object of preventing an oxidation which readily occurs in the presence of the alkali. After removal of the unattacked methyl iodide and the greater portion of the alcohol by distillation, the residue was treated with ether, and the solution washed with water. By now shaking with dilute alkali, a dull yellow extract was obtained, which, on acidification, yielded a semi-crystalline precipitate. The residual ethereal liquid ( B ) was reserved for subsequent examination. The product was collected and purified by crys- tallisation from alcohol :

Found, C = 61.93, 61.85 ; H =5*58, 5-34 ; CH,= 19.40. C , ;H,O?(O*CH?), requires C = 61.86 ; 13 = 5.15 ; CH, = 19-33 per cent.

It consisted of pale yellow needles, melting a t 161-162O, sparingly soluble in cold alcohol, and insoluble in cold alkaline solutions. If, however, to the pentamethyl ether suspended in dilute potassium hydroxide solution a little alcohol is added, the crystals now readily dissolve on shaking with the production of a yellow liquid, and the isolation of this compound in the manner above described was evidently due to the occurrence of some alcohol in the ether. Boiling concentrated potassium hydroxide solution also' dissolves this compound, and on cooling, the potassium salt separates as a yellow, colloidal precipitate. With sulphuric acid, quercetagetin pentamethyl ether forms a yellow liquid, which is reddened by the addition of nitric acid.

Acetylquercetagetin yentarnethyl ether crystallises from acebic

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214 PERKIN : QUERCE'I'AGEI'IN.

anhydride in colourless needles, melting a t 161--163O, and its solution in alcohol possesses a faint blue fluorescence.

Quercatage tin Henz m e t h yl Ether, C2,H2208.-T he ethereal liquid ( B ) , containing that portion of the methylation product undissolved by dilute alkali, was evaporated, and the viscous residue treated with a little methyl alcohol. On keeping overnight, the crystals, which had then separahed, were collected and recrystallised from the same solvent. The pale yellow product melted indefinitely between 130° and 140°, and as experiment indicated it t o be a mixture of the pentamethyl ether with a second substance, to remove the former i t was repeatedly crystallised from dilute alcoholic potassium hydroxide. In this manner, colourless, prismatic needles eventually separat'ed, which melted a t 141--143O, and appeared to be pure, but by recrystallisation froin acetone the melting point rose to 157-158O:

Found, C = 62.74 ; H = 5-50 ; CH, = 22.22. C,,H,O1(O*CH,), requires C=62.68 ; H =5*47 ; CH,= 22.38 per centt.

The compound f orms colourless iieedles, sparingly soluble in cold alcohol. The yield was extremely poor, although a considerable excess of alkali and iodide had been employed for the methylation, an indication that by this method it can only be produced with difficulty.

As it was desirable to prepare, if possible, some quantity of this hexamethyl ether, experiments were carried out on the action of methyl sulphate on the dry potassium salt of the pentamethyl compound, such a method having given good results in the case of quercetin (Waliasehko, Awh. Pharm ., 1904, 242, 242) and myricetin (Zoc. cat.), 0.8 Grain of quercetagetin peiitainethyl ether was added t o a,solution of 0-5 gram of potassium hydroxide in a little alcohol, the mixture evaporated to dryness, ground with 1.25 grams of methyl sulphate, and, after remaining overnight, treated with a further quantity of the sulphate. A t the end of the second day, the product was washed with ether, digested with boiling water, and crystallised from dilute alcoholic potassium hydroxide. The colourless, prismatic needles melted a t 141-142O, but after recrystallisation from acetone at 157--158O, and consisted of quercetagetin hexamethyl et'her, which, it thus seems probable, may be dimorphous. The yield (0.2 gram) was, however, again poor, and this could only be accounted for by the fact that the salt of pentamethyl ether, being soluble in alcohol, suffers hydrolysis during the evaporation of the solution to dryness. On the other hand, the salts of the corresponding quercetin and myricetin com- pounds are insoluble and not so readily attacked in this manner.

Querce tage t in Iiexaethtyl Eth,w, C,,H,,O,.-It has been shown,

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PERKIN : QUERCETAOETIN. 215

in the case of myricetin (Zoc. c i f . ) , and more recently with quercetin ahd other flavone colouring matters (P., 1912, 28, 328), that by the employment of excess of ethyl iodide and alkali, no difficulty is experienced in obtaining from these compounds good yields of their fully ethylated derivatives. A similar method was accordingly applied to quercetagetin, in the hope that a better result would be given than was the case with the methylation process. Ten grams of quercetagetin in 140 C.C. of alcohol were treated with 60 C.C. of ethyl iodide, and to the boiling mixture a concentrated solution of 24 grams of, potassium hydroxide in alcohol was added, drop by drop, during two days. After removal of the unchanged ethyl iodide and the greater portion of the alcohol, the residual liquid was poured into ether, the solution washed with water, then with dilute alkali, and evaporated. The almost colourless, crys- talline product, which melted a t 135--137O, was dissolved in hot alcohol, ct few drops of alcoholic potassium hydroxide were added, and the crystals, which separated on cooling, were collected. The pale yellow tint of the filtrate indicated the presence of a trace of the potassium salt of the pentaethyl compound. When obtained in this way, the substance was usually pure, and melted a t 139-141°, but a second treatment was sometimes necessary. The yield was 6-35 grams:

Found, C = 66.44 ; H = 7.43 ; Et = 35.47. C,,H,O,(OEt), requires C = 66.66 ; H = 7.00 ; Et = 35.80 per cent.

Quercetagetin hexaethyl ether forms colourless needles, sparingly soluble in cold alcohol. With mineral acids in the presence of boiling acetic acid, it readily yields oxonium compounds, the sulphate separating in orange needles, whereas the crystals of the hydrochloride possessed a somewhat more yellow colour. This behaviour is analogous to that of quercetin pentarnethyl ether (Wateon, P., 1911, 27, 163).

Hydro1 y& of Q uerce t crgetin Hexa et h y l E ther.-I f quercetagetin were in reality a flavonol derivative, the gentle hydrolysis of its hexaethyl derivative, by means of alcoholic potassium hydroxide, should, as has been previously shown to be the case with quercetin (Herzig, Ber . , 1909, 42, 156) and myricetin (Zoc. c i t . ) , yield products affording proof of such a structure.

Five grams of the substance, dissolved in a hot solution of 10 grams of potassium hydroxide in 50 C.C. of 80 per cent. alcohol, were heated on the steam-bath for seven hours. The liquid, which did not solidify on keeping (distinction from quercetin and myricetin), was evaporated to dryness, the residue dissolved in water, and the solution saturated with carbon dioxide. An oily product ( A ) thus separated, which was removed by ether, a4d

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216 PERKIN : QUERCETAQETIN.

weighed approximately 2-7 grams. The aqueous liquid, on acidifi- cation, gave a colourless, crystalline precipitate (B) (2.23 grams), and this was purified by recrystallisation (Found, C = 62.55 ; H = 7.04 ; Et; = 26.70. C,H,(OEt),=CO,R requires c= 62-85 ; H=6.66; Et=27.61 per cent.). It melted a t 167--169O, and con- sisted of protocatechuic acid diethyl ether. The oily product ( A ) , which only yielded crystals after keeping for some weeks, was drained on tile, and crystallised two or three times from minute amounts of methyl alcohol, the only solvent found suitable for the purpose, but in which it is somewhat readily soluble:

Found, C=61'22; H=7.75; Et=36*71. C16H2406 requires C = 61-53 ; H = 7-69 ; Et = 37.17 per cent.

This substance, for which the name of quercetagetol tetraethyl ether is suggested, consists of prismatic needles, melting a t 46--48O, soluble, although not very readily, in dilute alkali, indicating the presence of a free hydroxyl group. With acetic anhydride in the usual manner, it gave an oily acetyl compound, which up to the present has not become crystalline.

As it was to be anticipated that this compound contained a carbonyl group and should thus yield an oxime, a mixture of 0.56 gram of the substance, 1 gram of anhydrous sodium acetate, and 0'25 gram of hydroxylamine hydrochloride was digested with 25 C.C. of boiling alcohol for four hours (compare Lapworth and Steele, T., 1911, 99, 1884). After removal of the alcohol, the residue, on treatment with water, gave to ether an oily product, which on long keeping solidified, and was repeatedly crystallised from a mixture of light petroleum and carbon disulphide:

Found, C=58.74; H,O lost; N=4*38. C16H&N requires C = 58.71 ; N = 4.28 per cent.

This oxime consists of colourless needles, melting at 93-95O. With the object of obtaining further indication of the con-

stitution of the quercetagetol tetraethyl ether, 1 gram, dissolved in 50 C.C. ol' 2 per cent. potassium hydroxide solution, was gradually treated with a cold solution of 3 grams of potassium perman- ganate in 50 C.C. of water. Oxidation readily took place, but towards the end of the operation the pink coloration very slowly disappeared. The mixture was filtered, the precipitated oxide exhausted with boiling water, the clear liquid when cold saturated with carbon dioxide, and extracted with ether to remove traces of unattacked substance (if present). From the aqueous solution after acidification, ether now removed a small amount of a crystalline acid, and this, when recrystallised from water, formed colourless, prismatic needles, melting a t 100--102°, with the production of a

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PERKIN : QUERCETAGETIN. 217

clear liquid, which commenced to effervesce between 1 2 9 O and 1 3 6 O . Sufficient of this compound was unfortunately not available for analysis, but for purposes of future study, i t will be referred t o as querce tage t in ic acid.

Quercetagetin hexaethyl ether thus yields by the above-described method of hydrolysis diethylprotocatechuic acid (I), and a ketone, quercetagetor tetraethyl ether, which there is little reason to doubt, in view of the previous study of quercetin pentaethyl ether and myricetin hexaethyl ether (loc. cit.), possesses the constitution (IT) :

Quercetagetin is indeed, as its general reactions also indicate, a hexaliydroxyflavonol isomeric with myricetin. It differs, however, from this colouring matter, and. also from the closely allied quercetin in possessing a tetrahydroxybenzene in place of the phloroglucinol nucleus which they contain, as the following formula: indicate :

0 O H 0 O H

My icetin. Quercetagetin. With regard to the exact position of the hydroxyl groups in the

tetrahydroxybenzene nucleus of quercetagetin, which could occupy the positions: O:OH:OH:OH*=l: 2 : 3: 4, 1 : 3 : 4 : 5, 1 : 2 : 3 : 5, or 1 : 2 : 4 : 5, the evidence is scanty, and may be especially difficult to ascertain in the case of so rare a colouring matter.

According to Nierenstein and Wheldale (Ber., 1911, 44, 3487), quercetin when oxidised by chromic acid gives the quinone, quercetone (I), which by reduction is converted into the flavonol (11) :

0 0 O H H O 0 OH H/\/\C-/ \OH

H ()A/\g-<:>o€3 I C*OH I I \,/\/%*OH \- -/ Ho CO \/\/ *4j co

(1.1 (11.1 but as the latter compound melts a t 352--359O, its methyl ether a t 147-149O, sintering a t 136-13S0, and the acetyl compound could not be crystallised, it cannot therefore be quercetagetin.

On the other hand, the fact that quercetagetin pentamethyl ether is insoluble in alkali suggests that in this compound the un- methylated hydroxyl group occupies the position (5) and is adjacent to $he carbonyl group, although this again cannot yet be regarded

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21 8 PERKIX : QUERCE'I'AGETIN.

as certain because, whereas quercetagetin yields, although with difficulty, a hexamethyl derivative, no fully methylated flavonol compound possessing ail hydroxyl group in this position has pre- viously been obtained by the employment of methyl iodide and alkali. It is to be noted, however, that in almost every instance of this group hitherto studied a phloroglucinol nucleus has been present in the substances which it is quite reasona.ble to suppose might exert an influence in this respect not possessed by a tetra- hydroxybenzene group.

From a consideration of these points, it thus appears likely that quercetagetin is to be represented by one or other of the following formulze :

OH HO 0 OH

(1. ) (11 . )

Of these the second seems, at first sight, most probable, because should quercetagetin possess the pyrogallol grouping present in I, a more rapid oxidation of the substance in alkaline solution, with accompanying colour change, as in the case of myricetin, would be expected.

Dyeing Properties.-As is to be anticipated from its constitution quercetagetin readily dyes mordanted fabrics shades of a generally similar character to those given by other well-known flavonol colour- ing matters. A comparison of the dyeings given by this compound and quercetin on mordanted woollen cloth are, however, interesting, in that colours yielded by the l'ormer possess a distinctly yellower character.

Quercetagetiii Dull olive-yellow Yellow-orange Brown Brownish-hlsck Quercetin.. . . . . Orange-yellow Bright orsnge Redilish-brown Olive-black

Chromium. Aluminium. Tin. Iron.

This result is somewhat remarkable in that i t has been previously sliown that fisetin (trihydroxy-), quercetin (tetrahydroxy-), and myricetin (pentahydroxy-flavonol) yield practically identical colours, unless the duller and yellower shades given by quercetagetin are ascribed to slight oxidation during the dyeing .process. This, however, does not appear to be the case, for when chalk is employed during the operation no marked change of shade is observed, as is the case when dyeing with gossypetin (T., 1899, 75, 828). An important point in this respect is that quercetagetin, whatever tetra- hydroxybenzene group it may contain, possesses attached respec- tively to the nuclei A and B pairs of ortho-hydroxyl groups, each

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PERKlN : QUERCETAUETIN. 219

of which is capable of inducing a strong tinctorial effect with mordants. With a coiupound of this constitution, containing as i t does only a single chromophore, according to the quinonoid theory only one of these pairs can influence t.he dyciiig operation, although it is to be conceived that the quinonoid arrangement might vary in distinct lake particles. Thus, whereas it appears certain and has been discussed in former comw-inications that in quercetin the shades are mainly the result of the effect of the ortho- hydroxyl groups in its catechol nucleus (B) , it is probable, on the other hand, that the yellow colours given by quercetagetin are governed by the hydroxyl groups present in the nucleus ( A ) .

The more sparingly soluble colouring matter from the flowers, which was present in the crude quercetagetin to the extent of about 1 per cent., resembled rhamnetin (quercetin monomethyl ether) in appearance, but was not, as seemed probable, a methyl ether of qhercetagetin, for hydriodic acid indicated the absence of a methoxy-group. When crystallised from alcohol, it forms somewhat indefinite groups of minute needles, and dissolves in alkaline solu- tions with an orange colour, passing to green on dilution with water. Owing to the minute amount available, no further examination of this compound was attempted.

Dyeing Properties of the Flowers.-Employing mordanted woollen cloth, the following shades were obtained :

(‘liromirr 111. Aluminium, Tin. Iron. Yello\\ i 4 ~ - 1 1 t o u 11 Pale dull yellow Decl) ycllon--ornngc 12roiviliuh-black

These possessed a somewhat redder character than those given by quercitron bark, and were similar to, although not so red as, those from patent bark. I n this case the tinctorial effect is mainly due to glucoside.

Further work with quercetagetin will be carried out as soon as opportunity occurs, and an investigation of the isomeric and closely allied colouring matter gossypetin is in progress, the results of which it. is anticipated will throw further light on the exact structure of both compounds.

CLOTHWORKERS’ RESEARCH LABORATORY, THE UNIVERSITY, 1,EEDS.

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