Part 3 (1/2)

1 Natural wool fibre unproofed

2 Wool fibre showing proof on surface, filling up the cells and rendering the same dye-proof

3 Fur fibre fro dye deposited in cells and on the surface, bright and lustrous

4 Wool fibre as in No 2, with dye deposited on surface of proof

5 Section of proofed and veneered body, showing unproofed surface

6 Section of proofed body without ”veneer”]

LECTURE VIII

MORDANTS: THEIR NATURE AND USE

The name or word ”mordant” indicates the ee in which it was first created and used

It serves as a lande, which, by the way, needed land between scientific twilight and absolute darkness _Morder_ in French, derived from the Latin _mordere_,and printing believed their action to be merely aor corroding influence, serving to open the pores of the fabrics, and thus to give ress to the colour or dye

Mostsalts, and hence we must commence our study of mordants by a consideration of the nature of salts I have already told you that acids are characterised by e teretable and artificial colours, whilst bases or basic substances in solution, especially alkalis, restore those colours, or turn the, and the alkalis and soluble bases do the opposite The strongest and most soluble bases are the alkalis--soda, potash, and ammonia You all know, probably, that a drop of vitriol allowed to fall on a black felt hat will stain that hat red if the hat has been dyed with logwood black; and if you want to restore the black, you can do this by touching the stain with a drop of strong am acidity or alkalinity would not commend itself to an econoent for the purpose in extract of lit paper stained therewith The litht red by acids and blue by alkalis If the acid is exactly neutralised by, that is combined with, the alkaline base to form fully neutralised salts, the litents such as litmus are termed indicators A substance called phenolphthalein, a coal-tar product, is a very delicate indicator; it is more sensitive to acids than litmus is Now there are some salts which contain a preponderance of acid in their composition, _ie_ in which the acid has not been fully neutralised by the base; such salts are termed acid salts Bicarbonate of soda is one of these acid salts, but so feeble is carbonic acid in its acid properties and practical evidences, that we shall see both monocarbonate or ”neutral” carbonate of soda and bicarbonate or ”acid” carbonate of soda show evidences of, or, as chemists say, react with alkalinity towards lit alkaline with monocarbonate of soda, indicates the acidity of the bicarbonate of soda, a thing which, as I have just said, lit solution of monocarbonate of soda, and in the first ill put some phenolphthalein solution, and in the second, some litmus tincture The solution in the first jar turns rose coloured, and in the second, blue, indicating in each case that the solution is alkaline If noever, carbonic acid be blown into the two solutions, that in the first jar, containing the phenolphthalein, becomes colourless as soon as the monocarbonate of soda is converted into bicarbonate, and this disappearance of the rose colour indicates acidity; the blue solution in the jar containing lit in carbonic acid Further phenolphthalein, and which is acid towards that reagent, a little reddened litmus is added, this is still turned blue, and so still indicates the presence of alkali We have, therefore, in bicarbonate of soda a salt which behaves as an acid to phenolphthalein and as an alkali to litmus Another extremely sensitive indicator is the coal-tar dyestuff known as ”Congo red”; the colour changes produced by it are exactly the inverse of those produced in the case of litives a blue colour with acids and a red colour with alkalis

We have now learned that acids are as the antipodes to alkalis or bases, and that the two may combine to form products which may be neutral or may have a preponderance either of acidity or of basicity--in short, they ive you a yet clearer idea of these three classes of salts Now acids in general have, as we have seen, e may call a ”chemical appetite,” and each acid in particular has a ”specific chemical appetite” for bases, that is, each acid is capable of co with a definite quantity of an individual base The terms ”chemical appetite” and ”specific chemical appetite” are names I have coined for your present benefit, but for which chemists would use the words ”affinity” and ”valency”

respectively Now some acids have a e one, and the same may be said of bases, and thus as an example we may have mono-, di-, and tri-acid salts, or mono-, di-, and tri-basic salts In a tri-acid salt a certain voracity of the base is indicated, and in a tri-basic salt, of the acid Again, with a base capable of absorbing and co with its compound atom or molecule several compound atoms or molecules of an acid, we have the possibility of partial saturation, and, perhaps, of several degrees of it, and also of full saturation, which means combination to the full extent of the powers of the base in question Also, with an acid capable of, or possessing a sie absorptive faculty for bases, we have possibilities of the for to the siven to the molecule of such acid by the addition of a base We will now take as a simple case that of hydrochloric acid (spirits of salt), which is a monobasic acid, that is, itswith only one molecule of a monoacid base Hydrochloric acid may be written, as its name would indicate, HCl, and an addition even of excess of such a base as caustic soda (written NaOH) would only yield what is known as common salt or chloride of sodium (NaCl), in which the en (H) of the hydrochloric acid Now chloride of sodium when dissolved in water will turn litmus neither blue nor red; it is therefore neutral Such simple, neutral, monobasic salts are mostly very stable By ”stable” we encies, that, in the case of other salts, effect decompositions of those salts Such other salts which are decomposed more or less readily are termed ”unstable,” but the terms are of course only comparative

Now let us consider a di- or bi-basic acid Such an one is vitriol or sulphuric acid (H_{2}SO_{4}) The hydrogen atoms are in this case an index of the basicity of the acid, and accordingly the fully saturated sodium salt is Na_{2}SO_{4} or neutral, or better normal, sulphate of soda In like manner the fully saturated salt of the dibasic acid, carbonic acid (H_{2}CO_{3}), is Na_{2}CO_{3}, ordinary or normal carbonate of soda But we must observe that with these dibasic acids it is possible, by adding insufficient alkali to completely saturate theen atom of the acid is replaced by the metal of the base Thus sulphuric and carbonic acids yield NaHSO_{4}, acid sulphate or bisulphate of soda, and NaHCO_{3}, bicarbonate of soda, respectively An example of a tribasic acid is phosphoric acid, H_{3}PO_{4}, and here we may have three different classes of salts of three various degrees of basicity or base-saturation We may have the first step of basicity due to combination with soda, NaH_{2}PO_{4}, or monosodium phosphate, the second step, Na_{3}HPO_{4}, or disodium phosphate, and the third, and final step, Na_{3}PO_{4}, or trisodiurees of acidity, or rather the proportions of acid radicals in salts, due to the varying appetites or co powers of bases

Sodium only forms simple monoacid salts, as sodium chloride (NaCl), sodiu_ calcium chloride (CaCl_{2}); and aluminium and iron, triacid salts, for example, aluminium sulphate [Al_{2}(SO_{4})_{3}] and iron (ferric) sulphate [Fe_{2}(SO_{4})_{3}] Now in these triacid salts we can reroups and substitute the elements of water, OH, or hydroxyl, as it is called, for them Such salts, then, only partly saturated with acid, are termed basic salts Thus we have Al_{2}(OH)_{2}(SO_{4})_{2}, Al_{2}(OH)_{4}SO_{4}, as well as Al_{2}(SO_{4})_{3}, and we can get these basic salts by treating the normal sulphate [Al_{2}(SO_{4})_{3}] with sufficient caustic soda to remove the necessary quantities of sulphuric acid Now it is a curious thing that of these aluminium sulphates the fully saturated one, Al_{2}(SO_{4})_{3}, is theof its solution in water it suffers no change, but the more basic is the sulphate the less stable it beco or boiling its solution, giving a deposit or precipitate of a still more basic sulphate, or of hydrated alumina itself, Al_{2}(OH)_{6}, until we arrive at the salt Al_{2}(SO_{4})_{2}(OH)_{2}, which is quite unstable on boiling; Al_{2}(SO_{4})(OH)_{4} would be more unstable still This behaviour may be easily shown experimentally We will dissolve some ”cake alum” or normal sulphate of alumina, Al_{2}(SO_{4})_{3}, in water, and boil some of the solution No deposit or precipitate is produced; the salt is stable To another portion of the solution ill add some caustic soda, NaOH, in order to rob the normal sulphate of alumina of some of its sulphuric acid This makes the sulphate of alumina basic, and the more basic, the more caustic soda is added, the sodiu with the SO_{4} of the sulphate of alumina to form sulphate of soda (Na_{2}SO_{4}), whilst the hydroxyl (OH) of the caustic soda takes the position previously occupied by the SO_{4} But this increase of basicity alsothe solution, which now contains a basic sulphate of alumina, a precipitate is formed, a result which also follows if more caustic soda is added, production of still more basic salts or of hydrated alu place in either case

_Mordanting or Fixing Acid (Phenolic) Colours_--But what has all this to do with ? is possibly now the inquiry So much as this, that only such unstable salts as I have just described, which decompose and yield precipitates by the action on theencies, are suitable to act as true enerally, the sources or root substances of the best and h specific appetite or valency I think we have now got a clue to the principle of mordants and also to the i most effectively with them, and I may tell you that theis not a practical hest scientific attain, naue Professor Suida, did probably more than any other ion We have seen that with aluminium sulphate, basic salts are precipitated, _ie_ salts with such a predominance of appetite for acids, or such _quasi_-acids as phenolic substances, that if such bodies were present they would combine with the basic parts of those precipitated salts as soon as the latter were forether as one complex compound Just such peculiar _quasi_-acid, or phenolic substances are Alizarin, andprinciples of logwood, cochineal, Persian berries, etc Hence these substances will be combined and carried doith such precipitated basic salts The complex compounds thus produced are coloured substances known as lakes For exa basic sulphate of alumina, prepared as I have already described, and add to soet a red lake of Alizarin and alumina precipitated If I had taken sulphate of iron instead of sulphate of alumina, and proceeded in a similar manner, and added Alizarin, I should have obtained a dark purple lake Now if you ile fibre of a textile rasped the theory and purpose of h the alumina solution to fill the pores and tubes of the fabric; it is then passed through a weak alkaline bath to basify or render basic the aluminium salt in the pores; and then it is finally carried into the dye-bath and heated there, in order to precipitate the colour lake in the fibre The method usually e them eak solutions of the metallic salts used as mordants, often with the addition of acid salts, cream of tartar, and the like A partial decomposition of the metallic salts ensues, and it is induced by several conditions: (1) The dilution of the liquid; (2) the heating of the solution; (3) the presence of the fibre, which itself tends to cause the breaking up of the metallic salts into less soluble basic ones Thus it is not really necessary to use basic alu wool, since the latter itself deco, an insoluble basic sulphate being precipitated in the fibres of the wool (4) The presence of other added substances, as cream of tartar, etc The best alumina mordant is probably the acetate of alumina (”red liquor”), and the best iron mordant, probably also the acetate (”iron liquor”) (see preceding lecture), because the acetic acid is so har, etc

A further reason is that from the solution of acetate of iron or alu, and are thus readily deposited in the fibre

_Mordanting and Fixing Basic Colours_--Now let us ask ourselves a very important question Suppose we have a colour or dyestuff, such as Magenta, which is of a basic character, and not of an acid or phenolic character like the colours Alizarin, Haewood), or carminic acid (cochineal), and ish to fix this basic dyestuff on the tissue

Can we then use ”red liquor” (acetate of alumina), acetate of iron, copperas, etc? The answer is, No; for such a process would be like trying to combine base with base, instead of base with acid, in order to form a salt Combination, and so precipitation, would not take place; no lake would be formed We must seek for an acid or acid body to use as mordant for our basic colour, and an acid or acid body that will form an insoluble precipitate or colour-lake with the dyestuff An acid much used, and very valuable for this purpose, is tannic acid The tannate of rosaniline (colour principle of Magenta) is a tolerably insoluble lake, which can be precipitated by Magenta fro capable of displacing the soda But tannic acid, alone, does not forenta and the other basic dyestuffs, and so athese lakes more insoluble is needed It is found that tannic acid and tartar emetic (a tartrate of antimony and potash) yield a very insoluble compound, a tannate of antimony Perchloride of tin, in a similar manner, yields insoluble tannate of tin with tannic acid These insoluble compounds, however, have sufficient acid-affinity left in the combined tannic acid to unite also with the basic aniline colours, for very fast or insoluble colour lakes This principle is extensively used in practice to fix basic aniline colours, especially on cotton We should first soak the piece of cotton in a solution of tannic acid, and then pass it into a solution, say, of tartar emetic, when the tannic acid will be firmly fixed, as tannate of antimony, on the cotton We then dip the , for instance, Magenta, and it is dyed a fine red, coenta You now see, no doubt, the necessity of sharply discri matters, which we may term _colour acids_ and _colour bases_ respectively There are but few acids that act like tannic acid in fixing basic aniline dyestuffs, but oleic acid and other fatty acids are of the nuht now be asked, namely: ”Could the acid colour Alizarin, if fixed on cotton cloth, co_ Aniline Violet, and act as ait?” The answer is, ”Certainly”; and thus an Alizarin Purple would be produced, whilst if Magenta were used in place of Aniline Violet, an Alizarin Red of a cri of Wool and Fur_--In studying this subject I would recommend a careful perusal of the chapter on ”Mordants” in JJ

Hu of Textile Fabrics_, and pages 337 to 340 of Bowman's work on _The Wool-Fibre_

In the treatment of wool or fur with bi+chrome (potassium bi+chromate) we start with an acid salt, a bi+chroent, and we finish with a basic substance, namely, oxide of chromium, in the fibres of the wool or fur If we desire to utilise the whole of the chro liquor, we must add to it some sulphuric acid to set free the chromic acid from the potassium hich it is coives sulphate of potash and chromic acid The question of the proper exhaustion of bi+chromate baths is an important economic one Noe must remember that this chromic acid (CrO_{3}) oxidises our wool or fur, and must oxidise it before it can of itself act as areduced in the process to hydrated chromic oxide, Cr_{2}O_{3} + 3 H_{2}O [2 CrO_{3} (chroen)] It is this hydrated chromic oxide in the fibre that yields with the Haewood black dye Mr Jarmain finds that it is not safe to use ht of the wool) of bi+chromate; if 4 per cent be used, the colour becomes impaired, whilst if 12 per cent be ewood, the pheno the result of such excessive treatment I think there is no doubt, as Professor Hu , but I also think that there can be no doubt that the wool itself is also greatly injured and incapacitated for taking up colour Now the use of certain coal-tar black dyes in place of logwood obviates this use of bi+chro with it It also effects econo the use of bi+chrome, as well as of copper salts; but even thus, of course, other problems have to be solved before it can be finally decided which is best

LECTURE IX

DYESTUFFS AND COLOURS

_Classification_--In classifying the different dyestuffs and colouring matters it is, of course, necessary to consider first the properties of those colouring enerally, and secondly the particular reason forsuch classification The scientific che to theoretical considerations, as roups; the representative of iene would naturally classify them as poisonous and non-poisonous bodies; whilst the dyer will as naturally seek to arrange the to their behaviour when applied to textile fabrics But this behaviour on applying to textile fibres, if varied in character according to the che matter, as well as the chemical and physical nature of the fabric--and it is so varied--will , not a very simple matter

I may tell you that it is not a simple ement is that one which depends both on the action of the dyes on the fibres, and also on the intrinsic cheher branches of organic chemistry are involved in the consideration of the structure and dispositions, and consequently more or less of the properties of these dyes, you will readily cohest and best method of classification, particularly in the case of the coal-tar dyes, will be, anic chehest and bestthe dyestuffs affect the users, the dyers, in their processes?” In reply, I would say, ”I believe that the dyer who so understands the chemical principles involved in the processes he carries out, and in the bestthe dyes as chemical substances, so as to be able to act independently of the prescriptions and recipes given him by the dye manufacturers, and so be master of his own position, will, _ceteris paribus_, be the most economical and successful dyer” Manyto me, but, independently of this, I know it, and can prove it with the greatest ease Let me now, by means of an experiment or two, prove to you that at least soin with So different and varied are the substances used as colouring ards their chemical and physical properties, that they even act differently towards the same fibre I will take four pieces of cotton fabric; three of them are simple white cotton, whilst the fourth cotton piece has had certain um, printed on it in the form of a pattern, which at present cannot readily be discerned

We will now observe and note the different action on these pieces of cotton--(i) of a Turenta bath, and (iii) a madder or Alizarin bath The Turenta only stains the cotton cri ater alone, alain; the madder, however, stains the cotton with no presentable shade of colour at all, produces a brownish-yellow stain, removed at once by a wash in water But let us take the printed piece of cotton and dye that in the Alizarin bath, and then we shall discover the conditions for producing colours with such a dyestuff as madder or Alizarin Different coloured stripes are produced, and the colours are conditioned by the kind of metallic salts used Evidently the way in which, the turmeric dyes the cotton is different from that in which the madder dyes it The first is a yellow dyestuff, but it would be hard to assign any one shade or tint to Alizarin as a dyestuff In fact Alizarin (the principle of madder) is of itself not a dye, but it forms with each of several metals a differently coloured compound; and thus the metallic salt in the fabric is actually converted into a coloured compound, and the fabric is dyed or printed