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XXVI.—On the red colouring matters of madder

 

作者: Adolph Strecker,  

 

期刊: Quarterly Journal of the Chemical Society of London  (RSC Available online 1851)
卷期: Volume 3, issue 3  

页码: 243-256

 

ISSN:1743-6893

 

年代: 1851

 

DOI:10.1039/QJ8510300243

 

出版商: RSC

 

数据来源: RSC

 

摘要:

PELARGONIC ACID. XXVI.-On the Red Golouring Matters ~fMadder. BY ADOLPHSTRECKER. There is scarcely any class of bodies in organic chemistry the investigation of which is attended with so many diflFiculties as that of the colouring matters; this may account for the imper- fect knowledge we as yet possess of these substances excepting indigo which has been studied in every direction. Of many colouring matters Fe scarcely know more than the existence while of others we possess the percentage-composition translated into a more or less fitting empirical formula; a few only of these sub- stances have become of late so far accessible to us as to enable US to acquire a knowledge of them corresponding to the present demands * The same results are obtained in the distillation 6f ~alericacid.Comp. Chem. Soc. &I J. 111. R2 DR STRECKER ON THE of the science. This circumstance may be owing in some measure to the dificulty experienced in obtaining these substances in quan- tity sufficient for more accurate investigations as they generally occur distributed in small proportions only over a large amount of other matter besides vhich on the other hand the feebly defined and generally acid character of the colouring matters renders the preparation of definite compounds of them a matter of difficulty. Madder ranks in importance before all other colouring *principles ; the cultivatioii of the Rubia tinctoria the preparatlon of the madder and above all its manifold applications in the dyeing of cotton and in calico-printing in which it affords the most vai*ied beautiful and durable colours form important branches of agriculture and manufactures.Since Kuhlniann* first took up the chemical investigation of madder many chemists have applied their talents and powers to this subject; and it must bc gratefully acknowledged that the labours of Robiquet and Colin? Runge,j Schunck4 and Debus,fl have thrown much light on the chemical deportment of the active prin- ciples of the madder-root. A superficial contemplation of the results of these researches tvo~dcl certainly appear to point out a great want of accordance betwcen them; but on a mare strict examination the identity of the results may be discerned and the differences in the statements easily explained and adjusted.The study of the various researches on madder together with coniparative experiments made with this substance and with the splendid preparations of Messrs. Robiquet Schunck and Debus for the use of which I am indebted to Professor Liebig and Dr. Debus have shown me that madder contains-besides the yellow or orange colouring matters which do not play any important part in dyeing-two red colouring matters which have been obtained by chemists in a state of greater or less purity and have received from them various names The one of these first prepared by Robiquet and Colin and named by them AZizarine was afterwards obtained in a state of perfect purity by Runge who called it Madder-red. Persoz and * Ann. Ch. Phys.f23 XXIV 225. j-Ann. Ch. Phys. [2] XXXlV 225 j LXIII 306 $ J. Pr.Chem. V 362. 0 Ann. Ch. Pharm. LXVI 174. I/ Ann. Ch. Pharm. LXVI 351. 245 RED COLOURING MATTERS OF MADDER Gaultieis de Claubry,* obtained it in a state of less purity and described it under the name of Madi?re colorante rouge; and finally it was prepared perfectly pure by Schunck and Debus and called by the latter Lixaric acid. The second red cofouririg matter was first distinguished by Robiquet and Colin by the name of Purpurine although they did not obtain it pure ;it was first isolated by Runge and called by him Madder-purple. D ebus afterwards described it as Oxylizaric acid and lately Niggin? obtained it mixed with alizarine and described it under the latter name.Schunck has overlooked this substance; the correspondence of his analytical results vith those of Debus and some comparative experiments that I have instituted with the preparations of Schunck Debus and Robiquet show however that the alizarin of the first-named chemist is free from purpurine ;and it is very probable that in the treatment with concentrated solution of carbonate of potassa the purpurine was dissolved and only separated again in a decomposed form (possibly as alpha-or beta-resin). ALIZARINE. Alixarine is possessed of the following properties it may be obtained in two forms differing from each other in the amount of water which they contain. Hydrated alizarine occurs in small scales having the appearance of mosaic gold.The anhydrous substance has a red colour passing more or less into yellow according to the thick- ness of the crystals. This explains the difference in the statements of Debus Runge and Robiquet who describe it successively as occurring in aurora-red needles as a brownish-yellow powder and of the colour chromate of lead. It fuses when heated and sublimes in orange-coloured needles a portion being decomposed with deposition of carbon which may arise merely from the too rapid action of heat. It is moistened with difficulty by water and .vcrlien boiled with the latter dissolves with a deep yellow colour. The slightest trace of alkali (as ammonia or lime) colours the solution red; hence arises the fallacious statement of Robiquet that it dissolves in water with a rose-colour.It is considerably solnble in alcohol to which it imparts a yellow colour the solution becoming red under the same conditions as the aqueous solution. It dissolves likewise in ether with il yellom colour which is not altcred by the addition of small quantities of an * Ann. Ch.Phps. [2] XLVIXT 69. -f Phil. Mag. XXXIII 282. DR. STRECKER ON THE alkali the resulting red alkaline compound being insoluble in ether. Alizarine is easily soluble in alkalies; its solution in hydrate of potassa or of soda appears if snfficiently concentrated of a deep purple colour by transmitted light and pure blue by reflected light ; when highly diluted the solution assumes a uniform violet colour. This readily explains why Robiquet and Runge state the solution to be violet-coloured while Sc h unc k calls it purple-coloured Ali-zarine dissolves in ammonia and carbonate of ammonia with a colour similar to orchil the solution possessing no blue appearance on the surface.The cause of the difference in colour of the solutions of alizarine in caustic or carbonated alkalies evidently lies in the formation of different compounds of alizarine with the alkali. prepared one of these in the following manner Alizarine was dissolved by the aid of heat in a solution of carbonate of soda saturated in the cold ;the filtered solution deposited on cooling the compound of alizarine with soda insoluble in concentrated soda-solution. This was dried purified from an admixture of carbonate of soda by solution in absolute alcohol and precipitated from this solution in purple flakes by addition of ether.It dissolved easily in water and alcohol with the colour of orchil; the solution was coloured blue by addition of caustic soda. The compounds of alizarine with the alkalis are insoluble in cold concentrated salt solutions ; the ammoniacal solution of alizarine gives with chloride of barium a nearly pure blue flocculent precipitate; the solution from which the precipitate has been separated by filtration is colourless. Acetate of lead gives a purple-red pre-cipitate. A characteristic of alizarine is its insolubility in a cold solution of alum. When alizarine is boiled with a concentrated soln-tion of alum the liquid assumes a yellow colour like that of an aqueous solution of alizarine; on cooling the small quantity of alizarine that was dissolved separates again the liquid becoming almost colourless.Alizarine forms a red solution in hydrated sulphuric acid and is reprecipitated unchanged on the addition of water. Robiquet and Schunck have shown that alizarine is capable of producing on mordantized cloth all the colours obtained from madder. To conclude from this that alizarine is the only active dyeing principle in madder would certainly be going too far; for it will be presently shown that purpurine likewise yields durable and beautiful colours on mordantized cloths. The results of the analysis of alizarine by Schunck and Debus correspond exactly-nor does the older analysis by Robiqu et differ considerably from their numbers.Schiel’s results however RED COLOURING MATTERS OF MADDER. 247 cannot be made to correspond with them. The percentage-com-position of alizarine may perhaps be considered as established by the more recent analyses ;but in the construction of its chemical formula we meet with the difficulty of determining the equivalent of a weak acid by the preparation of neutral compounds. Schunck was led by the analysis of a lead-salt to the formula while Debu s assigns to another lead-cornpound the formula 2 PbO. C, H 0, and represents alizarine itself by the formula c30 H,o 0,. I believe I can prove that the chemical formula of alizarine is '20 H6 O6 which corresponds with sufficient accuracy with the percentage-compo- sition of this substance and its compounds and is likewise confirmed by the results of the decomposition of alizarine.The composition of alizarine dried at loo*-120° is as follows Equiv. Calc. Sch un ck. Found. Debus. (-A- (-A- C2 H 68-96 3-95 69.09 3.88 69.15 4.04 6924 4-11 6895 3-79 68.98 3-80 6878 3.78 27.26 27.22 27.20 0 27.59 27.03 26.81 26.75 100*00 100*00 100.00 lOO*OO 100.00 100*00 99.96 Schunck has also submitted hydrated alizarine to analysis; it lost on desiccation 18.3 p. c. of water which when calculated upon the above formula corresponds nearly to 4equivalents of water calculated (17.1 p. c.). The composition of hydrated alizarine is therefore C, H O6 +-4 HO. Equivalent. Calc. Found (Schunck). c20 57.14 58.97 56-94 57.02 4.76 8-19 5.13 5-87 HI0 -m OlO 38-10 --.100*00 The amount of carbon found corresponds exactly with the calcu- lated number; the discrepancy in the amounts of hydrogen found arises from the use of warm chromate of lead in the first aualysis while in the two latter the substance was even mixed in a cold mortar. DR. STRECKCR ON THE The composition of the compounds obtained by precipitating an amrnoniacal solution of alizarine with chloride of calcium and chloride of barium and when dried at 1004 corresponds to the following formula Lime-compound . . 2 0,) + 3 (CaO. HO) Calc. Found. (S chu n ck.) Percentage of lime . . 18.3 18.30 18.58 ~~ry~a-co~po~n~ . . 2 (C20H 06) -+ 3(BaO. HO) Calc.Found. Percentage of baryta . 38.0 38.03 Schunck’s lead-compound corresponds most nearly with the formula 2 (C20H 0,) +3 PbO Calc. Found (Schunck). Carbon . . . . . 36.1 37.5 36.9 Hydrogen. . . . . 1-5 1.7 1.6 - . . . . 12-1 -Oxygen . Protoxide of lead . . . 50-3 49.1 49.8 100.0 The lead-compound analysed by Deb us contains the aIizarine and protoxide of lead in another proportion which (when the sub-stance is dried at 120O) may be expressed by the formula -t-4 PbO. Calc. Found (Debus). Carbon . . b . 38.2 38.18 38.51 Hydrogen . . . . 1.6 1.97 1.98 Oxygen . . . . 12.8 -Protoxide of lead . . 47.4 47.62 -i00.0 Of the products of decompositioq of alizarine one only is accurately known that naniely which is produced by various oxidizing agents and has been described by Schunck under the name of Alizaricacid.Laurent and Gerhardt* have recently pointed out the close corre- spondence of alizaric acid in its properties and composition with Phtalic acid. By treating garancine with nitric acid these chemists obtained an acid the ammonia-salt of which yielded on sublimation a substance similar to phtaliniide in all its properties. * Compt. Rend. par Gcrhardt et Laurent 1849,222. ,)0H,(C203 RED COLOURING MATTERS OF MADDER. Hence they are of opinion that no doubt can exist with respect to the identity of alizaric and phtalic acids. I am enabled to quote some quantitative determinations which prove the identity of the acid obtained from alizarine and of phtalic acid.I am indebted to Professor Liebig for a specimen of alizaric acid prepared by Schunck himself. It accords perfectly in its physical properties with the acid obtained from naphthaline. The silver-salt of the acid dried at looo furnished on analysis the following numbers I. 0.4465 grms. of the salt burnt with chromate of lead gave 0.4195 , , carbonic acid and 0.0455 , , water 11. 0.4475 , , gave on careful ignition 0.2540 , , of silver. 111. 0,5443 , , gave. 0.3090 , , of silver. The silver-salt explodes when rapidly heated; this may be avoided by heating it gently and lighting it with a piece of burning paper. These numbers correspond in 100 parts with the composition of the phtalate of silver.Equiv. Calculated. Found. I. 11. 111,-Carbon 16 96 25.3 25.6 -.-.I Hydrogen . 4 4 1.0 1.1 -Oxygen . . 8 64 16.9 -- . 2 216 56.8 -56.7 56.8 Silver 30 380 100.0 Schun ck's analysis of his akaric acid and pyro-alizaric acid (anhydrous phtalic acid) may be quoted as further proofs of the identity of the two acids. The formula of phtalic acid is C, H6o, and that of anhydrous phtalic acid is c16 H 0,. Phtalic acid. Anhydrous phtalic acid. Calc. Mean Calc. Found. In 100 parts c16 57.8 57-5 64.9 64.0 JY 1) 3) H6 3.6 3.9 H 297 3.1 0 32-4 ->> JY IJ '€3 3806 -100.0 100.0 If we compare the formula of alizarine with that of its product of DR. STRECKER ON THE oxidation it will be found that 4 equivalents of carbon have been eliminated and that 2 equivalents of oxygen have entered into the compound.Alizarine . . . '20 O6 Phtalic acid . . . C, H 0 Difference . . C 0 The 4 equivalents of carbon are probably eliminated in the form of oxalic acid as the latter is obtained in considerable quantity in the treatment of madder with nitric acid The decomposition of alizarine by nitric acid is expressed by the following equatiou U u-ALizarine. Phtalic acid. Oxalic acid. The new formula of alizarine brings to light a close connection between this colouring matter and a substance obtained by Laureut,s in his elaborate research on the metamorphoses of naphthaline namely Chloronuphthalicacid. Tbe latter substance is Chlorinated Alizarine as will be seen by the comparison of their formuls Alizarine.. . . . C, H 0 Chloronaphthalic acid CzO {!f} 0 That the apparent relation exhibited by the fomuh of these substances really exists is proved by the close analogy of their properties and products of decomposition. The acid character of alizarine is only feeble that of chloronaphthalic acid is more strongly marked as is generally the case with chlorinated com-pounds. The ChZoronap~~~aZ~c acid of Laurent is a yellow substance almost insoluble in water dissolving in alcohol and ether in larger but still not very considerable quantity. It fuses at 200°,and may be sub- limed without change. It dissolves in concentrated sulphuric acid without undergoing decomposition. Its combinations with metallic oxides exhibit lively colours extending from yellow to bright red.Solution of potassa dissolves chloronaphthalic acid with a deep red colour. A concentrated solution deposits on cooling a crimson salt crystallized in needles whose formula according to Laurent is KO. CzoH C10,. The ammonia-salt is similar to the foregoing. * Rme Scientifique XIII. RED COLOURING MATTERS OF MADDER. 25 1 The baryta-salt is obtained by double decomposition in the form of golden-yellow needles of silky lustre which when dried at looo,have the formula BaO. C, H C10,. The lime-salt is obtained like the other salts by double decompo- sition ;it crystallizes in orange-coloured needles The strontia-salt has the same colour. Protochloride of mercury gives a red-brown precipitate ;solution of alum an orange-coloured ;solution of protoxide of lead a reddish- yellow; and solution of oxide of silver a blood-red precipitate becoming carmine red and crystalline when heated.Salts of the protoxides of cobalt and copper give carmine-coloured precipitates. Chloronaphthalic acid dyes neither mordantized cloth nor cotton mordantized or oiled for turkey red. This might have been expected the acid character of the substance being already too strongly defined. The close similarity of character between chloronaphthalic acid and alizarine-a similarity which is found only in the nearest substitution products-is further supported by the corresponding decomposition of these two substances by nitric acid.According to Laurent chloronaphthalic acid is converted by treatment with nitric acid into oxalic and phtalic acids. C,,H,C1O,+4!HO3.0,=C,,H,O,$-C,H,Os+ HC1. v Chloronaphthalic acid. Phtalic acid. Oxalic acid. The only difference consists in the simultaneous elimination of chlorine and its substitution by hydrogen. It is possible however that instead of phtalic acid a chlorinated phtalic acid was formed in which case the decomposition would correspond still more closely with that of alizarine C, H,C106 +2 HO +0 =C16H,ClO +C H 0,. Laurent has also obtained besides this chloronaphthalic acid a acid (C20{c1&} p~~uc~~~rona~ht~ali~ OJ which likewise yields carmine-coloured salts insoluble in Gater. I have myself obtained in the preparation of naphthalic acid an acid which did not yield with solution of baryta the usual golden-yellow baryta-salt but a splendid purple-red compound.I had too small a quantity of sub-stance at my command for an analysis; it was probably a bi-or terchloronaphthalic acid. I obtained simultaneously with this sub-stance a chlorinated phtalic acid which has not been described DR STRECKER ON THE hitherto I prepared the potassa-salt of this acid by saturating a boiling alcoholic solution with solution of potassa ; it quickly separated in small plates of silvery lustre which when dried at 140° gave on analysis the following numbers 0.4045 grm. of potassa-salt gave 0.2175 , , sulphate of potassa. 0.3495 , ,,potassa-salt burnt with chromate of lead gave 0.3890 , , carbonic acid and 0.0215 , ,,water These determinations correspond with the composition of bi-chlorophtalate of potassa.CaIc. Found. C, . . 30% 30.4 H . . 0.6 0.7 Cl 22% I 0 . . 20.6 -K 25.1 24.3 loooo The question now arose whether it would be possible to expel the one equivalent of chlorine from chloronaphthalic acid and to replace it by hydrogen. Two methods in particular are known for obtaining the original substance from chlorinated compounds. lSIelsens* reconverted chloracetic into acetic acid by the action of potassium-amalgam (I of potassium to 150 of mercury). The potassium dissolves without evolution of gas as long as any chlorine is contained in the organic substance in place of which hydrogen is taken up.Kolbet made use of the galvanic current for the same purpose and with great success; he passed the current into the neutral liquid by means of two amalgamated zinc plates. I have endeavoured to obtain alizaric acid from chloronaphthalic acid by both these methods without homcver arriving at the desired result. If potassium-amalgam is brought in contact with chloro- naphthalic acid and water the liberated potassa soon dissolves the acid forming a dark red liquid which however never exhibits the blue colour of the alizarine solution by reflected light. After a time the solution contained chloride of potassium and the colour of the solution diminished in intensity. A yellow precipitate was obtained * Ann. Cb. Phjs.[3] X 233. t Ann. Ch. Pharm. LIV 274. 253 RED COLOURING MATTERS OF MADDER. by the addition of an acid which proved to be unaltered chloro-naphthalic acid as it yielded with solution of baryta the beautiful golden-coloured needles already mentioned. A portion of the acid had undergone a deconiposition which was however not limited to the substitution of hydrogen for the atom of chlorine but had at once proceeded further. The insolubility of chloronaphthalic acid in slightly acidulated water precluded its decomposition in such a solution by the galvanic current. When subjected to the current in an alkaline solution chloronaphthalic acid soon underwent a change which was indicated by the decrease in the colour of the solution and the assumption of a brown coloration as also by the presence of cblorine in the liyid.But in this case likewise no alizitrine could be detected at any period of the operation. Although these experiments have led to no positive results I have no doubt that continued exertions and the application of new agentg will lead to a reaction the results of which will be more within reach of the means presented to us by the science. Chloronaphthalic acid was prepared by Laurent by treating the compound C, H C1 (chlorzcre de chloronaphtase) with nitric acid. Chlorine is passed over naphthaline until the mass at first in a state of fusion has assumed an unctuous consistence when the chloride of naphthaline is dissolved out by ether and obtained by evaporation of the ether in the form of an oily liquid.This is submitted for several days to a current of chlorine the resulting viscid matter being rendered more fluid towards the end of the operation by the applicatiori of heat. After the action is complete the substance is dissolved in boiling ether which on cooling deposits the chlorinated chloride of naphthaline; this is boiled with nitric acid till it no longer solidifies on cooling but remains in the form of a viscid mass. A yellow powder is separated by the addition of ether to which Laurent has given the name oxyde de c7zZorox~~zaphtose. Vhen treated with an alcoholic solution of potassa this substance is imme-diately converted into chloronaphthalic acid. These reactions may be expressed by the following equations c, €1 + C1 = C, H C15 + H C1.-+i-) Naphthaline. Chlorinated cliloi-ide of naphthaline. C, H?CI + 0 = C, H C120 -1-3 H C’f. + v Chloi inated chloride Oside de chloroxi-of naphthaline. IIaphtose. 254 DR STRECKER ON TEE C, H Cl 0,+ 2 KO = C, H C1 KO + K C1. Lvv-d -v-Oxide de 'chloroxi-Chloron&h thalate naphtose. of potassa. Now it is evident that if chloride of naphthaline (C2 H Cl,) were to be submitted to these reactions the final product would also contain 1 equivalent of chlorine less and 1 equivalent of hydrogen more; in fact alizarine (C2 H 0,) must then be obtained instead of C, H C1 0,. In the treatment of the chlorinated chloride of naphthaline by nitric acid a large quantity of the substance is converted into further products of decomposition namely into phtalic and oxalic acids.The chlorinated compounds withstand the oxidizing action of nitric acid much better than the normal substances and this may be the reason why chloride of naphthaline yields instead of C, H 0, only the products of decomposition of that substance namely phtalic and oxalic acids. The experiments of Schunck have shown that alizarine when boiled with nitric acid splits up readily into phtalic and oxalic (?) acids. I do not know whether I shall be able to follow up this subject; I believe however to have pointed out with sufFxient clearness in the foregoing the manner in which we may hope to obtain alizarine from naphthaline. The method would be to check the reaction at a certain point; this might be arrived at by the employment of a more feeble oxidising agent than nitric acid as the latter always effects a further decomposition.The theoretical and practical interest of the above question leads me to hope that chemists will bestow a little attention upon it. If it be considered that according to the experiments of Robiquet and Schunck alizarine not only produces the same colours as madder but even possesses advantages over the raw material; if besides this the small amount of alizarine required for dyeing and the low price of naphthaline obtained as it is in large quantities in the manufacture of coal-gas be taken into consideration it will be evident that even if a very elaborate and circuitous method should be requisite for the conversion of naphthaline into alizarine its practical application might still be found advantageous.PURPURINE. This second red colouring principle of madder differs from alizarine chiefly by its solubility in solution of alum. If a concen- trated solution of alum be boiled with purpurine the latter dissolves with il fine bright red colour; the solution has an orange colour by reflected light. Ammonia precipitated a red-lake varying in RED COLOURING MATTERS OF MADDER. colour when dry from rose to ponceau according to the qaantity of alumina present. The solubility of purpurine in solution of alum has been applied by Runge and Debus to the separation of this substance from alizarine. Purpurine differs in appearance ac- cording to the conditions under which it crystallizes.It is deposited from its solution in strong alcohol in red needles and from weak spirits in thin soft orange-coloured needles forming a matted mass when dried. These orange-coloured crystals contain water of crystallization which they part with at looo assuming a red colour. A specimen of pure purpurine containing however some red crystals (anhydrous purpurine) in admixture lost 4.9 of water at 120°. Runge describes his purpurine as occurring in orange- coloured crystallized grains and D e b us his oxylizaric acid as forming red needles from 2 to & of an inch in length. Purpurine is more easily soluble in warm water than alizarine and forms a red solution. It fuses when heated and sublimes with deposition of carbon.Its solution in alcohol has likewise a much deeper red colour than that of alizarine; it dissolves in ether and in concentrated sulphuric acid. Purpurine* may be easily distinguished from alizarine by the colour of its solution in potassa; it is bright red and does not possess the blue tint characteristic of alizarine. Purpurine gives purple- coloured precipitates with lime- and baryta-salts which are easily distinguishable from those of alizarine. The lead-compound is likewise purple. Piirpurine is also insoluble in a concentrated solution of carbonate of soda in the cold; it dissolves on ebullition but separates again perfectly from the solution on cooling. The com- pound of purpurine with potassa- (?)alkali is also insoluble in other salt -solutions.Runge has already shoton that purpurine dyes cloth purple when mordantized with alumina rose-coloured with tin-mordant ponceau-coloured with lead-mordant and violet with iron-mordant I have convinced myself that purpurine imparts to stuffs mordantizcd with alumina as well as to cotton which has been oiled and mor-dantized for turkey-red a fine deep red dye without any blue tint and that these colours are not altered by the process of raising with soap. It cannot therefore be doubted that purpurine plays a part in turkey- red dyeing as well as in the common-madder dyeing. D ebus has published several concordant analyses of purpurine (oxylizaric acid) which correspond exactly to the formula c, H 05 * I am not able to confirm the statement made by Schiel that sublimed madder- purple (purpurine) dissolves with a blue colour in solution of potassa.Purpurine repeatedly sublimed dissolved in potassa with a bright red colour. DR STRECKER ON MADDER To a lead-compound of purpurine he has assigned the formula PbO C, H 0,. It has already been seen with alizarine how little reliance can be placed on the atomic weights derived from compounds of bodies like these of feebly acid properties; the equivalent proportion C H 0 determined upon by Deb u s seems however undoubtedly correct and the most probable formula appears to be C, H 0,. Hydrated purpurine would contain according to the above determination one equivalent of water of crystallization (calc.5.3per cent). A certain connection between two substances occurring in the same plant and so similar in properties to each other might rea-sonably be expected. Debus interpreted the compositioii of alizarine and purpurine as found by him by assuming the presence of one atom more of oxygen in the former than in the latter; the endeavours to convert alizarine into purpurine by the action of oxygen were not attended with the expected result. The following experiment would however seem to indicate a reconversion of alizarine into purpurine. Some madder from Elsars was suspended in watcr mixed with fresh yeast and kept for some time in a closed vessel at atempcrature of about 30°. Fermentation was soon set up as was indicated by the brisk evolution of carbonic acid.After the lapse of two days the action terminated-the liquid was powerfully acid-and when distilled yielded alcohol and a trace of a volatile acid ;the strongly acid residue contained much phosphoric acid. The liquid was separated from the solid portion by a cloth; the solid matter removed and treated with a boiling solution of alum which assumed the exact colour of purpurine. On cooling the solution deposited besides crystallized alum a red colouring matter which dissolved again when boiled with more solution of alum and contained besides purpurine a mere trace of alizarin. The addition of sulphuric acid to the alum-solution separated a considerable quantity of purpurine which after extraction with boiling hydrochloric acid yielded from its alcoholic and ethereal solutions crystals of purpurine mixed with an amorphous substance.The alizarine appeared therefore to have disappeared while a considerable quantity of purpurine was obtained. It would however be necessary in order to prove decidedly whether alizarine is converted into purpurine by fermentation to submit pure alizarine mixed with yeast to fermentation.

 

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