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- TABLE DES MATIÈRES
- RECHERCHE DANS LE DOCUMENT
- TEXTE OCÉRISÉ
- PAGE DE TITRE (Première image)
- Lecture I, Tuesday, February 7th, 1871 : Red colouring substances, madder (p.3)
- Lecture II, Tuesday, February 14th, 1871 : Red colouring substances (continued) (p.7)
- Lecture III, Tuesday, February 21st, 1871 : Blue colouring substances (p.12)
- Lecture IV, Tuesday, February 28th, 1871 : Quercitron, Fustic, Persian Berries, Weld, Aloes, Turmeric, Annatto, Ilixanthine, Lo-Kao, Tannin matters, Gall nuts, Sumach, Divi-Divi, Myrobalans, Catechu (p.18)
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12
LECTURE III.—DELIVERED TUESDAY, FEBRUARY 21ST, 1871.
BLUE COLOURING SUBSTANCES.—INDIGO, ORCHIL, CUDBEAR, LITMUS, PRUSSIAN BLUE, AND ULTRAMARINE.
Indigo.—1This most valuable dyeing substance was used as a dye-stuf in India and Egypt long before the Christian era, and the Romans were acquainted with it, although they only used it as a pigment, not knowing how to render it soluble, and so available for dyeing. It is only since the sixteenth century, or from the time of the discovery of the passage to India round the Cape of Good Hope, that it has become generally known in Europe ; and its employment as a dye was greatly re-tarded by the opposition it met with from the large vested interests of the woad cultivators, who induced the English, French, and German governments to pro-mulgate several enactments against its use. So severe were some of them, that Henry IV. of France issued an edict, condemning to death any one who used that pernicious drug called the “ devil’s food.” It is only since the year 1737 that the French dyers have had the right of using indigo without restriction.
Indigo exists in several varietics of plants, among which may be mentioned the Polygonium tinctorium and the Isatis tinctoria, or woad ; but, as in the case of nearly all the dye-stuffs already spoken of, it is found most abundantly in plants of the leguminous order. It is ex-tracted commercially from the genus Indigofera, varieties of which grow abundantly in India, Java, China, and in some of the South American States.
To extract the indigo which the plant contains, it is mowed when in full flower, made into bundles, and carried into large vats containing water. Fermentation ensues, which is allowed toproceed for eight or nine hours, when the liquor, which was yellow at the beginning of the operation, assumes a dark green colour, forming a blue scum on the surface. This liquor is then run of into shallow vats, where it is violently agitated with sticks, stirred by men or women, or with a dasher, which produces the same resuit, the conversion of the white, soluble indigo into blue insoluble indigo. A little lime-water is now added, and the whole allowed to rest. The blue indigo thus deposited is boiled with water, when a scum, composed of vegetable and animal matters, cornes to the surface, and is removed. The blue paste is thrown on a filter, pressed, and placed in wooden frames, which are divided into small squares, where the indigo is allowed to dry first in the sun, and afterwards in the shade. The quality of the indigo produced dépends mainly on the care bestowed on its manufacture.
Until 1855 we had no correct ideas as to the state in which the indigo existed in the indigofera plants, nor of the changes which it underwent during the process of extraction. It had been stated by M. Chevreul, many years before, that white indigo was oxidised into blue. But in the above year, and subsequently, in 1857 and 1865, Dr. Schunck published a séries of papers, in which he described the true nature of the Chemical. changes which take place in the manufacture of indigo. He operated on the Isatis tinctoria, or woad, which contains the same colour-giving principle as the Indigofera and is the only plant yielding indigo that grows freely in this country.
By these researches, he demonstrated that indigo existed in the plants, combined with a sugar, forming a glucoside, to which he gave the name indican; this com-pound, under the influence of fermentation in the manu-facturing process, was unfolded into indigo and sugar. By treating the dried woad with ether or alcohol, Dr. Schunck obtained indican, and, among other processes for its extraction, gives the following simple one. He treats the pounded dried woad leaves with ether in a displacement apparatus, and distils of the greater part of the ether. The remaining green liquor is then evaporated at a moderate température, a little cold water added to the syrupy residue, and the insoluble chlorophyl and other matters separated by filtration. The yellow liquid thus obtained is evaporated, either spontaneously or in vacuo.
Indican is a yellow, transparent, glutinous solid. As may be seen from the above, it is soluble in alcohol, ether, and water. When boiled with caustic alkalies, it evolves ammonia, but its most remarkable and interesting property is that of yielding indigo blue when treated with strong acids. If sulphuric or muriatic acid be added to its water solution, no change whatever is perceptible for some time. But on heating to near the boiling point, the solution immediately becomes sky-blue. On boiling for a short time, the solution becomes opalescent. On continuing to boil, it acquires a purple colour ; and then, provided the solution is tolerably con-centrated, a copions deposit of dark purple flocks is formed. These are collected on a filter, and washed with water. By treating the washed flocks with alcohol, Dr. Schunck obtained pure indigotine, and a reddish blue substance was dissolved, called by Berzelius indigo-red, and by Schunck indirubine, which may be considered as a product of the décomposition of indican.
The colour-giving principle of the plant may be considered, like those of the dyewoads, as a glucoside, yielding by its décomposition a colourless principle, which is afterwards converted into a colour. Dr. Schunck explains by the following formula the décomposition of indican into indigo :—
Indican. Water. Indigo. Indiglucine.
CaHsoN 01s + H2O = C8H5N O + 3 (CgH1oO6)-
In 1864 he published a most valuable paper, throwing much light on the manufacture of indigo, and the management of what is called a woad vat. In it he gives the Chemical actions which take place, and explains why, if the indigo manufacturer does not take the greatest care in conducting the process of fermentation, to extract the indigo from the plant, he will either get an inferior quality of indigo, or a great decrease in the yield of the product, or even in some cases entirely lose the colouring matter. He shows that these résulta take place when the fermentation in the vats is allowed to be either too rapid or too prolonged, in which cases not only is indican decomposed, but the indiglucine, or sugar, is converted into alcohol and acetic acid ; and he shows that the indigo combines with this alcohol and
Le texte affiché peut comporter un certain nombre d'erreurs. En effet, le mode texte de ce document a été généré de façon automatique par un programme de reconnaissance optique de caractères (OCR). Le taux de reconnaissance estimé pour cette page est de 98,69 %.
La langue de reconnaissance de l'OCR est le Français.
LECTURE III.—DELIVERED TUESDAY, FEBRUARY 21ST, 1871.
BLUE COLOURING SUBSTANCES.—INDIGO, ORCHIL, CUDBEAR, LITMUS, PRUSSIAN BLUE, AND ULTRAMARINE.
Indigo.—1This most valuable dyeing substance was used as a dye-stuf in India and Egypt long before the Christian era, and the Romans were acquainted with it, although they only used it as a pigment, not knowing how to render it soluble, and so available for dyeing. It is only since the sixteenth century, or from the time of the discovery of the passage to India round the Cape of Good Hope, that it has become generally known in Europe ; and its employment as a dye was greatly re-tarded by the opposition it met with from the large vested interests of the woad cultivators, who induced the English, French, and German governments to pro-mulgate several enactments against its use. So severe were some of them, that Henry IV. of France issued an edict, condemning to death any one who used that pernicious drug called the “ devil’s food.” It is only since the year 1737 that the French dyers have had the right of using indigo without restriction.
Indigo exists in several varietics of plants, among which may be mentioned the Polygonium tinctorium and the Isatis tinctoria, or woad ; but, as in the case of nearly all the dye-stuffs already spoken of, it is found most abundantly in plants of the leguminous order. It is ex-tracted commercially from the genus Indigofera, varieties of which grow abundantly in India, Java, China, and in some of the South American States.
To extract the indigo which the plant contains, it is mowed when in full flower, made into bundles, and carried into large vats containing water. Fermentation ensues, which is allowed toproceed for eight or nine hours, when the liquor, which was yellow at the beginning of the operation, assumes a dark green colour, forming a blue scum on the surface. This liquor is then run of into shallow vats, where it is violently agitated with sticks, stirred by men or women, or with a dasher, which produces the same resuit, the conversion of the white, soluble indigo into blue insoluble indigo. A little lime-water is now added, and the whole allowed to rest. The blue indigo thus deposited is boiled with water, when a scum, composed of vegetable and animal matters, cornes to the surface, and is removed. The blue paste is thrown on a filter, pressed, and placed in wooden frames, which are divided into small squares, where the indigo is allowed to dry first in the sun, and afterwards in the shade. The quality of the indigo produced dépends mainly on the care bestowed on its manufacture.
Until 1855 we had no correct ideas as to the state in which the indigo existed in the indigofera plants, nor of the changes which it underwent during the process of extraction. It had been stated by M. Chevreul, many years before, that white indigo was oxidised into blue. But in the above year, and subsequently, in 1857 and 1865, Dr. Schunck published a séries of papers, in which he described the true nature of the Chemical. changes which take place in the manufacture of indigo. He operated on the Isatis tinctoria, or woad, which contains the same colour-giving principle as the Indigofera and is the only plant yielding indigo that grows freely in this country.
By these researches, he demonstrated that indigo existed in the plants, combined with a sugar, forming a glucoside, to which he gave the name indican; this com-pound, under the influence of fermentation in the manu-facturing process, was unfolded into indigo and sugar. By treating the dried woad with ether or alcohol, Dr. Schunck obtained indican, and, among other processes for its extraction, gives the following simple one. He treats the pounded dried woad leaves with ether in a displacement apparatus, and distils of the greater part of the ether. The remaining green liquor is then evaporated at a moderate température, a little cold water added to the syrupy residue, and the insoluble chlorophyl and other matters separated by filtration. The yellow liquid thus obtained is evaporated, either spontaneously or in vacuo.
Indican is a yellow, transparent, glutinous solid. As may be seen from the above, it is soluble in alcohol, ether, and water. When boiled with caustic alkalies, it evolves ammonia, but its most remarkable and interesting property is that of yielding indigo blue when treated with strong acids. If sulphuric or muriatic acid be added to its water solution, no change whatever is perceptible for some time. But on heating to near the boiling point, the solution immediately becomes sky-blue. On boiling for a short time, the solution becomes opalescent. On continuing to boil, it acquires a purple colour ; and then, provided the solution is tolerably con-centrated, a copions deposit of dark purple flocks is formed. These are collected on a filter, and washed with water. By treating the washed flocks with alcohol, Dr. Schunck obtained pure indigotine, and a reddish blue substance was dissolved, called by Berzelius indigo-red, and by Schunck indirubine, which may be considered as a product of the décomposition of indican.
The colour-giving principle of the plant may be considered, like those of the dyewoads, as a glucoside, yielding by its décomposition a colourless principle, which is afterwards converted into a colour. Dr. Schunck explains by the following formula the décomposition of indican into indigo :—
Indican. Water. Indigo. Indiglucine.
CaHsoN 01s + H2O = C8H5N O + 3 (CgH1oO6)-
In 1864 he published a most valuable paper, throwing much light on the manufacture of indigo, and the management of what is called a woad vat. In it he gives the Chemical actions which take place, and explains why, if the indigo manufacturer does not take the greatest care in conducting the process of fermentation, to extract the indigo from the plant, he will either get an inferior quality of indigo, or a great decrease in the yield of the product, or even in some cases entirely lose the colouring matter. He shows that these résulta take place when the fermentation in the vats is allowed to be either too rapid or too prolonged, in which cases not only is indican decomposed, but the indiglucine, or sugar, is converted into alcohol and acetic acid ; and he shows that the indigo combines with this alcohol and
Le texte affiché peut comporter un certain nombre d'erreurs. En effet, le mode texte de ce document a été généré de façon automatique par un programme de reconnaissance optique de caractères (OCR). Le taux de reconnaissance estimé pour cette page est de 98,69 %.
La langue de reconnaissance de l'OCR est le Français.