Orchil paste, orchil extract, and cudbear are obtained by exposing the plants (species of lichens) containing the colouring principle, called Orcin, itself a colourless substance, to the joint action of ammonia and air, when the oxygen of the air changes that orcin by oxidising it into Orcèin, which is the true red colouring matter contained in the preparations named. The lichens thus treated acquire gradually a deep purple colour, and form the products called "cudbear." This dye works best in a neutral bath, but it will do what not many dyes will, namely, dye in either a slightly alkaline or slightly acid bath as well. Orchil is not applicable in cotton dyeing. Being a substantive colour no mordants are needed in dyeing silk and wool with it. The colour produced on wool and silk is a bright magenta-red with bluish shade.
Litmus is also obtained from the same lichens as yield orchil. It is not used in dyeing, and is a violet-blue colouring matter when neither acid nor alkaline, but neutral as it is termed. It turns red with only a trace of acid, and blue with the least trace of alkali, and so forms a very delicate reagent when pieces of paper are soaked with it, and dipped into the liquids to be tested.
Safflower: This vegetable dyeing material, for producing pink colours on cotton without the aid of a mordant, consists of the petals of the flower of carthamus tinctorius. It contains a principle termed "Carthamin" or "carthamic acid," which can be separated by exhausting safflower with cold acidulated water (sulphuric acid) to dissolve out a yellow colouring matter which is useless. The residue after washing free from acid is treated with a dilute solution of soda crystals, and the liquid is then precipitated by an acid. A red precipitate is obtained, which fixes itself directly on cotton thread immersed in the liquid, and dyes it a delicate rose pink, which is, unfortunately, very fugitive. Silk can be dyed like cotton. The colour is not fast against light.
Turmeric is the root portion of a plant called curcuma tinctoria, that grows in Southern Asia. The principle forming the colouring matter is "Curcumin." It is insoluble in cold water, not much soluble in hot, but easily soluble in alcohol. From the latter solution it separates in brilliant yellow crystals. Although the colour it yields is very fugitive, the wool and silk dyers still use it for producing especially olives, browns, and similar compound shades. It produces on cotton and wool a bright yellow colour without the aid of any mordant. To show you how easily dyeing with turmeric is effected, I will warm some powdered turmeric root in a flask with alcohol, and add the extract to a vessel of water warmed to about 140° F. (60° C.), and then dip a piece of cotton in and stir it about, when it will soon be permanently dyed a fine bright yellow. A piece of wool similarly worked in the bath is also dyed. However, the unfortunate circumstance is that this colour is fast neither to light nor alkalis. Contact with soap and water, even, turns the yellow-dyed cotton, reddish-brown.
Annatto is a colouring principle obtained from the pulpy matter enclosing the seeds of the fruit of a tree, the Bixa orellana, growing in Central and Southern America. The red or orange colour it yields is fugitive, and so its use is limited, being chiefly confined to silk dyeing. The yellow compound it contains is called "Orellin," and it also contains an orange compound called "Bixin," which is insoluble in water, but readily soluble in alkalis and in alcohol with a deep yellow colour. To dye cotton with it, a solution is made of the colour in a boiling solution of carbonate of soda. The cotton is worked in the diluted alkaline solution whilst hot. By passing the dyed cotton through water acidulated with a little vitriol or alum, a redder tint is assumed. For wool and silk, pale shades are dyed at 106° F. (50° C.) with the addition of soap to the bath, dark shades at 200° to 212° F. (80° to 100° C.).
LECTURE X
DYESTUFFS AND COLOURS—Continued
Artificial Substantive Dyestuffs.—You may remember that in the last lecture we divided the colouring matters as follows: I. Substantive colours, fixing themselves directly on animal fibres without a mordant, only a few of them doing this, however, on vegetable fibres, like cotton. We sub-divided them further as—(a) those occurring in nature, and (b) those prepared artificially, and chiefly, but not entirely, the coal-tar colouring matters. II. Adjective colours, fixing themselves only in conjunction with a mordant or mordants on animal or vegetable fibres, and including all the polygenetic colours. III. Mineral or pigment colours. I described experiments to illustrate what we mean by monogenetic and polygenetic colours, and indicating that the monogenetic colours are mainly included in the group of substantive colours, whilst the polygenetic colours are mainly included in the adjective colours. But I described also an illustration of Group III., the mineral or pigment colours, by which we may argue that chromate of lead is a polygenetic mineral colour, for, according to the treatment, we were able to obtain either chrome yellow (neutral lead chromate) or chrome orange (basic lead chromate). I also said there was a kind of borderland whichever mode of classification be adopted. Thus, for example, there are colours that are fixed on the fibre either directly like indigo, and so are substantive, or they may be, and generally are, applied with a mordant like the adjective and polygenetic colours; examples of these are Cœrulein, Alizarin Blue, and a few more. We have now before us a vast territory, namely, that of the b group of substantive colours, or, the largest proportion, indeed almost all of those prepared from coal-tar sources; Alizarin, also prepared from coal-tar, belongs to the adjective colours. With regard to the source of these coal-tar colours, the word "coal-tar," I was going to say, speaks volumes, for the destructive and dry distillation of coal in gas retorts at the highest temperatures to yield illuminating gas, also yields us tar. But, coal distilled at lower temperatures, as well as shale, as in Scotland, will yield tar, but tar of another kind, from which colour-generating substances cannot be obtained practically, but instead, paraffin oil and paraffin wax for making candles, etc. Coal-tar contains a very large number of different substances, but only a few of them can be extracted profitably for colour-making. All the useful sources of colours and dyes from coal-tar are simply compounds of carbon and hydrogen—hydrocarbons, as they are called, with the exception of one, namely, phenol, or carbolic acid. I am not speaking here of those coal-tar constituents useful for making dyes, but of those actually extracted from coal-tar for that purpose, i.e. extracted to profit. For example, aniline is contained in coal-tar, but if we depended on the aniline contained ready made in coal-tar for our aniline dyes, the prices of these dyes would place them beyond our reach, would place them amongst diamonds and precious stones in rarity and cost, so difficult is it to extract the small quantity of aniline from coal-tar. The valuable constituents actually extracted are then these: benzene, toluene, xylene, naphthalene, anthracene, and phenol or carbolic acid. One ton of Lancashire coal, when distilled in gas retorts, yields about 12 gallons of coal-tar. Let us now learn what those 12 gallons of tar will give us in the shape of hydrocarbons and carbolic acid, mentioned as extracted profitably from tar. This is shown very clearly in the following table (Table A).