104 THE JOURNAL OF THE SOCIETY OF DYERS AKD COLOURI&TF. [Aug.25.1888

2& per cent.

5 I.

10 I .

20 I.

40 .,

PROF. J: J. HWMMEL IN THE CHAIR.

0’38 percent. I 2’12 per crnt. Methyl-orange

1’51 ,, 1 2’83 ,, 637 ,, 3’63 ,,

15‘87 ,, 4’13 ,, 35’18 ,, 4‘82 ,,

COMMUNICATIONS FROM THE CHEMISTRJ AND DYEING DEPARTMENT OF THE BRADFORD TECHNICAL COLLEGE.

BY EDMUND KNECHT, PILD., F.I.C.

V.-On tlie Absorption of Certain Acids, Bases ant Salts, by Wool, Cotton, and Silk. 0. Furdenbager and J. R. Appleyard.

IT is well known that the textile fibres, notably thost of animal origin, possees the remarkable property o absorbing certain acids, bases or salts from dilutc aqueous solution. This fact has long been known not only to practical men,.but also to chemists; bui t h e actual extent to which such absorption takec place has not hitherto h e n invehgated exhaustively and in no case has there (to my knowledge) been ar attempt to explain the phenomenon on a chemica basia

The fiist quantitative determinations appear tc have been undertaken by Chyreul, and an accounl of them is published in the Dictionnaire Techno logique,” vol. xxi. p. 365 (about the Sear 1833) Chevreul finds that wbeq wcol cr silk is s:eeped in a dilute solution of acid ot known strength, the solu- tion becomes weaker; in the case of cotton, the solution bewmes stron er. He states, further, that the acid can be re novef from the tibra by continued washing.

Bolley, in his “ Kritische und Experimentelle BeitrLge zur Theorie der Fiirberei ” (Ziirich. 1559). confir6s Chevreul’s results as regaids s o d and silk, but finds that cotton is without any action on weak acids.

The most recent investigation on the subject is the elaborate work of Mills and Takamine, published in the “Journal ot the Chemical Society March, 1883), and entitled, “ On the Absor tion of 2 eak Reagents by Cotton, Silk, and Wool.” t h e latter authors divide the results of their investigations into : ( 1 ) The rate and amount of absorption of individual reagents ; and (2) the ratio of absorption of mixed reagente. They have determined, with a great degree of accuracy, the actual and relative amounts of sulphuric acid, hydrochloric acid and cauatic soda absorbed in certain fixed units of time by cotton, silk, and wool. The chief results arrived at are, that when wool is treated with dilute hydrochloric acid and dilute caustic soda (the solutions containing equal molecules of each reagent), the absorption takes place in the proportion of 2HC1 : 3NaOH. The correspondin roportions for siik and cotton are 3HCl: 10Na88. The relative amounts absorbed by cotton and silk are :-

Cotton Silk. Sul huric acid .................. 1 2‘0

rochloric acid .............. 1 2 8 2’3 Caustic soda .................... 1

H J

In conclusion, the authors express the hope that, their investigation, ‘‘ while bearing on the one hand on questions of great technical importance, ma not be without its value in the profounder stuiy of cotton, silk and wool- three bodies of definite chemical composition, but whose intimate constitu- tion still remains obscure.JJ

The assertion that wool and silkare definite chemical compounds requires, in my opinion, a stronger con- firmation. The various kinds of wool, for instance, which have been analysed possess, it is true, a similar percentage composition, but it is scarcely

~~ _ _ _ - . _

admissible to represent the chemical coniposition of this fibre by the formula C,,H,,,N,SO,,, as the authors have done, especially when the percentages of theconstituting elements vary by as much as 2 in the different analyses. Wool is an organised structure, and when its chemistry has once been properly investi- gated it will doubtless be found to consist, like other orgalised structures, of a number ot distinct bodies, which have, however, not hitherto been isolated or recognised on account of their insolubility in the ordinary solvents.

As a purely scientific treatise, the work of Dr. Mills and M. Takamine is, no doubt, valuable; but for practical purposes it will scarcely be found as useful as the authors anticipate, es ecially with regard to the tem eratures a t which tge degrees of absorption were itermined. No dyer would, for ingtance, think of employing a temperature of 4 O C. or 820 in wool dyeing. It is difficult to under- stand why the authors did not a t least t r the boiling temperature, so as to throw some lie{ 0 t on what actually takes place in practice. Anothcr important Foint which they seem to have overlooked ie the dekermination of the tenacity with which these fibres withhold the various agents exp.riniented with. It was, therefore, chiefly with a view of throwing some additional light on thissubject that we undertook the somewhat lengthy and tedious eeries of expriments, the result of which I am about. to detail :-

The wool used in our experiments waa a scoured unbleached flannel, containing 15 per cent. of moisture. The ash contained :

W O N per cent. calcium as CaO. 0224 ,, potash as KzO.

When boiled for a length of time (ahout one hour) in distilled water, it left the solution perfect1 neutral to Congo-red, litmus, methyl-orange, a n 8 phenol- phthalein.

The cotton used was a boiled and bleached cotton yarn. The silk was ungummed spun silk.

ABSORPTION OF ACIDS, ALKALIR, AND SALTS BY WOOL.

Since the results of these experiments were ntended to throw some light on what takes lace in ,he treatment of all-wool and mixed goods, t!e tem- perature employed was in each case 1000, which is ilightly above that actually used in dyeing on the large scale, but sufficiently near to be able to draw analogies.

The percentages given in the following tables refer to the weight of the wool. The amount of liquid :mployed was in all cases the same-viz., 5OOcc. for jgrms. of wool. The time of treatment was also miform-viz., 1 hour in each case.

Absoytion of Sulphurit Acid by Wool.

Acid 1 absorbed. Indicator. Acid Acid left in employcd . solution.

. A W 14 1818.1 THE JOURNAL OF THE SOCIETY OF DYERS AND COLOUHTSTS 105

- -

Sodium chloride.. .... 970

19'40

Calcium chloride ...... 9'00

40 per cent. are used the proportion is as 1 : 8'3. I n the ordinary process of acid dyeing we may take it, therefore, that from 2 to 3 per cent. of sulphuric acid is absorbed by the wool. The greater part of this actually remains in the wool if soft water is used for washing off, The tenacity with which the acid is withheld by the fibre is readily seen from the results of the following two experiments :-

A quantity of wool was first boiled for one hour in 6 per cent. sulphuric acid. I t was then removed, washed lightly with distilled water (back into the original solution) and boiled, for the !mpose of removin the absorbed acid, for one hour i n distilled water. %his was repeated a second and third time, with the following results :-

Amount of acid left in solution 1'40 per cent. . 1st boiling out .................. 0'81 .,

2nd ,, ................. 0'34 .. ................. 0 0 s ,( 3rd ,. Total free acid boiled out.. .. 1'28 ,,

If this latter figure is added to the amount of free acid left in solution, we get 2'66, which, when sub- tracted from the amount originally employed, leaves 2'34 as re resenting the percentage of acid per- manently aisorbed or neutraliscd The amount of

, free acid retained, even after having boiled for an hour in distilled water,. is noteworthy, and shows the great tenacity with which the wool retains the acid. The tendering of cotton war s in mixed goods is, no doubt, frequently due to tks property.

Absorption of Hgdrochloric Acid by Wool. The same conditions were adhered to a3 in the

-

previouv series of experiments. - ___-__

_ _ _ ~ 3% 0'29

9'4; 0'23

18'6) 017

8W 0'01

Indicator. Acid I Acldleft in Acid employed. solutlon. absorbed.

7 9 4 per:oent.

16'88 ,, 83.81 ,,

4'84 per cent.

675 ,, 9'13 ,, 11% 0 11'85 1,

3'10 per cent. Phenolphthalem

~. -

By KOH and Phenolphthalein. By AgNoa

Amount of free acid loft in solution .................... 4'83 per cent. 5'00 per cent.

Alum SO, in so, employed. solution. absorbed.

5 per cent. 0'0 per cent. 25'42 Per Cent. -

10 I , 3'3 ,, 22'10 1,

15 ,. 108 ,, 14'60 ,, 14'4 ,, 11'00 ,, 20 11

1st boiling out.. .............. 1'29 .. 2nd .................. 055 ,, 3rd .................. 037 ..

Indicator*

Phenolphthalein

t

4th ;, ................ 012 ,, 5th . . . . . . . . . . . . . . . . . . 008 6th ,, ................ neutral ..

1'36 0'67 0.38 0'18 0'17 0'02 - -

Total acid boiled out .... 2'39 .. 7'78 ,, Original amount of acid

Lett in solution and boiled .................. .. employed 7 9 4 7-94 A,

out .......................... 7 1 2 .. 7.78 I , - -- Permanently absorbed or

neutralised ................ 0 7 2 .. 016 ,, Absorption of Caudc Potash by Wool. .

Alkall I Alkallleftln 1 Alkell Indicator, employed. solutlon. combined.

I I I -

~~~~~

A fresh uantity of wool was now boiled with e& er cent.ckOH, washed lightly and extracted with baing water.

Amount of KOH lcft in sohtion.. ...... 1'38 per cent. 1st boiling out .......................... 0'49 ,, .......................... 0'28 ,. 2nd ,, .......................... 0'16 ,, 3rd ,, 4th .. .......................... 0'11 ,, .......................... 0'07 ,. 5th ,.

Total KOH boiled out ..,.. .......... 1'11 ,, _ _

Total KOH employed.. .................. 2'33 ,, KOH left in solution and boiled out .... 2'49 ,, _- KOH permanently absorbed or neu-

tralised ................................ 0'01 ,, These results show that the affinity of wool for

alkalis is not nearly so great as for acids. The amount of alkali permanently absorbed or neutra- lised is practically nil.

We next studied the absorption of certain neutral salts, with the following results :-

1 Amount Left in taken. 1 solution. I Absorbed'

A curious result was obtained on boiling wool with 10 per cent. of its weight of magnesium sulphate. The solution after boiling was alkaline, in fact its alkalinity was equivalent to 0'52 per cent. MgO. What reactions have actually taken place here it would be difficult to conjecture, but the result is of interest if only as an additional proof of the great affinity which wool exhibits towards sulphuric acid.

Wool boiled in a solution of 10 per cent. tartar (chemically pure) left 5'6 per cent. in solution, and absorbed 4.4. Of this only 0'12. er cent. could be removed by boilin out once w i i distilled water. The estimation of t%e tartar was done with caustic potash and phenolphthalein as indicator.

Bchaviour of Wool towards a Xolutwlz of Alum. Potash alum contaids theoretically 25'42 per cent.

SO, combined with alumina. The alum used in our experiments was titrated with normal caustic soda, using phenolphthalein as indicator, and was found to contain 25'40 per cent. SO3. Usin Congo- red as indicator we.obtained 25'30 per cent. f0,.

The percentages in the following table refer to the weight of alum employed:-

It is seen from this that in mordanting with alum alone a considerable quantity of sulphuric acid is absorbed by the wool; where only 5 per cent. of alum was employed, the whole of the sulphuric acid was absorbed.

A fresh quantity of wool was now boiled in 16 per cent. alum for olie hour, taken .out rinsed lightly, and extracted repeatedly with disti!fed water. The titrations were done wlth caustic potash, using phenolphthalein rn indicator.

106 THE JOURNAL OF THE SOCIETY OF DYERS AND COLOURISTS. [Aug.,%, 1W.

397 per cent.

7'94 (, 15'88 (,

Amount left in solution (as SOn) ........ 11'20 per cent. 1st boiling out .......................... 3'32 ,, 2nd 19 .......................... 1'20 I,

3rd .. .......................... 1'04 I ,

4th .......................... 0.60 1,

......................... 0'44 ,, 6th *I

Total boiled out .................... 7'12 ,, In solution .............................. 11'20 ,, Total remaining in solution ........... 18'32 ,,

6th :: .......................... 052 1,

-

-

By subtracting this figure from the total amount of sulphuric acid originally present as A1,(S04),, we get :-

Tots1 802 as dla(SO4) 25'42 per cent. ,, in solution' : : : : : IS*% ,, -

2'25 1'72 Methyl-orange.

5'85 2'09 I ,

12'22 3%

7'10 ,, SO, combinedor neutralised.

This ap ears to speak for the fact that a basic sulphate of alumina and not free alumina has been fixed by the fibre.

I n another experiment, a fresh quantity of wool was again boiled in 16 per cent. alum. The alumina left in solution was then precipitated with ammonia and estimated in the usual manner.

AlzO, left in solution ...................... 0'0355grm. Amount of SO, left in solution (calculated) 11'20 per cent. SOr combined with Alto3.. ................ 11'02 ,, Free sulphuric acid (as SOn) in solution .... 018 ..

The results of these ex eriments with alum only prove more exactly what faa long been known-viz., that when wool is boiled in a solution of alum, a basic salt becomes fixed on the fibre, while free acid remains in solution. The acidity of the solution is, however, not nearly so great as is usually supposed to be the case.

EXPERIMENTS WITH COTTON. Sulphuric Acid-Cotton boiled under conditions

similar to those observed with wool in 5 per cent. of its weight of sulphuric acid! absorbed 1.9 per cent., leavin 3'1 per cent. in solution. On boiling out in fresh $istilled water the cotton lost only further 0'2 per cent.

-

H,SO .o ' inallypreeent 59percent. ,, fefi%solutionand boiled out ...... 3'3 .. -

1'7 ,, absorbed or neutralised. I n a second experiment, cotton was boiled in 10 per

cent. aulphuric acid, then boiled out three times in succeasion.

Amount left in solution ............ 6'57 per cent. 1st boiling out ...................... 0'25 ,, ...................... 0'10 ,, 2nd 9, ...................... 0% .. 3rd 1 )

Total boiled out.. .... 0'40 ,,

,: -

Tota! H.SO,.originally taken 10'00

H,SO, abaorbed or neutralised.. .... 3'03 ,, Left in solution and boiled out ' :: :: 6'97 -

Whether the sulphuric acid is here merely mechanically absorbed or chemically combined we have not hitherto decided. Neverthelass the com-

aratively large amount of sulphuric acid absorbed !y cotton and not removable by boiling with water, is noteworthy.

Caustic PotasA.-For caustic alkalis cotton doea not a pear to have any affinity. A quantity of cotton boilea in 2'5 per cent. caustic potash left 2.49 per cent. in solution, and consequently only absorbed 0'1 per cent.

Calcium Chloride.-For neutral salts like this there a pears to be absolutely no attraction on the part of t i e cotton. Cotton boiled with 9 per cent. calcium chloride did not absorb any a t all.

-~

EXPERIMENTS WITH SILK. The experiments with silk were confined to the

absorption of hydrochloric, tartaric and sulphuric acids.

H $ $ ~ ~ ~ i c HCl in solution. HCI absorbed. Indicator.

Tartaric Acid.-Silk treated for an hour in 25 per cent. tartaric acid a t about 50" C. left 22'5 er cent. in solution ; 2'5 per cent. waa consequently aisorbed.

Sulphuric Acid.-Silk boiled for one hour in 20 per cent. sulphuric acid gave :-

In solution ........................ 185 per cent. Absorbed ......................... 1'5 ,,

CONCLUSIONS. To sum up briefly, the following conclusions may

be drawn from the results of this investigation :- 1. Wool, silk, and cotton all ossess the property

of absorbing acids from dilute soktion. At a boiling temperature the affinity of sul huric acid seems to be reatest for wool, after whicg follows cotton, and last$ silk. By boiling with water the free acid is partially extracted from the fibres.

2. In the case of wool, a t least, the absor tion seems to be due to a chemical combination. Tfis is partly proved by the presence of combined ammonia in the solution in which the material has been boiled, but more definite1 by the result! obtained with hydrochloric acid, hactically no acid is permanedy absorbed ; it can all be removed by continued boiling. That which we considered at first to be ermanently absorbed is simply neutralised by some \ask coneti- tuent or constituents of the fibre. The absorption of chjomic acid by wool in mordantin with bichromate of potash or soda is analo ous, an$ is probably a h , as pointed out last year, 8ue to chemical combina- tion." 3. Wool absorbs considerably more caustic potash

than cotton, but it can all be removed by boiling with water.

4. When boiled with 15 per cent. alum wool effects a partial decom osition of the salt, leaving free acid in solution. T i e amount of the latter is, however, very small. The alumina and sulphuric acid appear to be absorbed in about equivalent proportions.

VI.-On the Behaviour of Animal Fibres towards the Acid Colouring Matters.

IN a former ccmmunication I discussed the chemical changes which take place when wool is dyed with the basic coal-tar colours. At the end of the communi- cation I ventured to express the opinion that both wool and silk are highly complicated organic compounds, or mixtures of compounds. In all pro- bability they contain carboxyl and amido-groups which are capable of combining with the colour bases and colour acids respectively to form coloured lakes. Taking into account the extremely complicated nature of these fibres and the obscurity in which their chemistry is up to the present involved, I had at the time very little hope of getting any clearer proofs of my theory. From the results of our experi- ments on the absorption of acids by wool-i.e., chiefly by the rapid decrease in the ratio of acid absorbed to acid employed-I was led, however, to suppose that

* This Journal, p. 118,188i.

Aw. 25,1888.1 THE JOURNAL OF THE SOCIETY OF DYERS AND COLOURISTS. 107 ~~ -__

there must be some compound in the stbstance a the wool which possesses strongly basic propertier and which not only combines with these colourles acids, but also with the colour acids or acid coal-ta colours.

I believe now to have isolated this lake-producinl com ound by the following simple method : 1OOgrma woofwere boiled for about two hours with 2Wgrms strong sulphuric acid and 3Wgrms. water. Afte about 30 minutes the wool begins to dissolve, and a the end of two hours all is dissolved with the excep tion of a slight residue. The light brown solutioi was filtered and examined. With most of fhe acic coal-tar colours it produces richly coloured precipi tates, which are inso!uble, or. sparingly soluble,. ii water, easily soluble in alkalis, and are reprecipi tated by acids from the alkaline solution Tannic acid produces a voluminous dirty whitc precipitate, while bichromate of potash produces I yellow crystalline precipitate. Alum and coppe: sulphate are without action, even in presence of ai excess of sodium acetate. The only two lake, examined more closely were those obtained wit1 crystal scarlet 6R and soluble blue.

The crystal scarlet lake weighed about 10 per cent of the weight of the wool dissolved. It forms shinins scales which are so intensely coloured as to appea almost black in reflected light, but the red colour ii easily seen in transmitted light.

It is insoliible in dilute sulphuric acid, slightlj soluble in boiling water, from which it separates ou a in on cooling in the form of microscopical wnrtr w%ch are of an intense scarlet colour. In dilutc ammonia it dissolves easily, but is reprecipitatec unchanged by the addition of hydrochloric acid. I r strong sulphuric acid it dissolves with a blue-violei colour,which on dilution with water is rendered turbic and red again. In ether and bisul hide of carbpr it is insoluble, and is sparingly solub?e in alcohol.

The soluble hlue lake forms scales with a copperj reflex which show similar properties to those of thc scarlet lake.

Indigo extract also produces a precipitate, which is however, entirely soluble in hot water, but separatei out again on cooling.

A solution of cochineal and stannous chloride pro duce an insoluble scarlet precipitate.

The first question which now naturally presented itself was, What is this lake- roducing substance ? B carefully neutralising the sup huric acid solution wid

when filtered, washed, and dried was obtained in thc form of a hard, brown, amorphous mass, difficultly soluble in acids, but easily soluble in caustic alkalis. It ives similar reactions to the ori inal sulphuric acif solution and is no doubt either w%olly or in part the lake-producing substance. I a t first thought that it must be either leucine or tyrosine, two well-known decomposition products of wool, but I found this not to be the case, since neither of these substances gives in solution the slightest indication of a precipitate with either crystal scarlet or soluble blue. Hitherto I have not had the time to investigate the matter further, but I hope shortly to have an oppor- tunity of investigating more closely the compo- sition of this lake-giving substance. The same or a similar compound seems to be produced from silk since the solution of this fibre in equal proportions o! sulphuric acid and water gives a similar precipitate with crystal scarlet. A freshly-prepared solution of

latine is not affected by crystal scarlet, but after g v i n g been boiled for two or three hpurs with. dilute sulphuric acid it yields a copious precipitate with the scarlet solution.

caustic soda, I obtained a c \ eesy precipitate, which

By dissolving wool in caustic soda, acidulating the solution with sulphuric acid and filtering from the somewhat copious preci itate thus formed, I obtained a clear, almost colourfess solution, which showed similar properties to the one just described. It yields a copious cheesy white precipitate with tannic acid, and a yellow grecipitate of similar consistency with bichromate o potash. Soluble blue is com- pletely precipitated.

By dissolving wool which had been dyed with about 50 per cent. cr stal scarlet in the same pro ortions of sulphuric aciB and water as those usef before, a violet-coloured solution was obtained from which on diluting with water apparently the same scarlet lake was precipitated as the one just referred to.

Although I do not claim to have proved conclu- sively that the lake-giving aubstance which I have isolated actually exists as such in the wool, it never- theless appears highly probable that such is the case after the wool has undergone a treatment with acid. It is well known that wool boiled (mordanted) in sul- ehuric acid can be dyed with the acid scarlets, yellows,

lues, etc., but this will a t once be attributed to the free acid retained by the wool. But this is not the case, as will be seen from the result of the following experiment :-A small piece of wool was boiled with 10 per cent. of its weight of siilphuric acid for one hour. I t was then taken out,washed and boiled for one hour in 100 times its weight of distilled water. This latter o eration was repeated until, after the ninth boiling o f an hour's duration with fresh distilled water, the water was absolutely neutral to methyl-oran e. This leaves no doubt that the wool now containe8 no free acid. On dyeing in 2 per cent. crystal scarlet without any addition of acid, the wool showed a considerably fuller and more even shade than another pattern dyed with 2 per cent. of same dyed along with 24 per cent. sulphuric acid. In the former case the bath was not exhausted. The chemical changes which take place here are probabl the reverse, but analogous to those which we have siown to take place in dyeing animal fibres with basic coal-tar colours.

An estimation of the sodium in the crystal scarlet 4R used in these experiments showed it when dried to be as nearly as ossible a chemically pure product, corresponding to tge formula CzoH, 2NzSz0,Na,.

Now every practical dyer knows that when wool is boiled in a neutral solution of these acid dyes it merely becomes tinttd. Crystal scarlet forms no exception to this rule. Even when the dye-bath is made up with sufficient sulphuric acid to neutralise the sodium contained in the dye (0'2 er cent. acid for 2 per cent. dye), the result is scarceg appreciably better. Nor is double this amount sufficient to pro- duce a full shade, and practical experience has shown that the minimum amount necessary to produce the fullest shade is from 2 to 3 per cent:, or from 20 to 30 times as much acid as would theoretically be necessary to liberate the free colour acid. No attempt has hitherto been made, to my knowledge, to explain why mch a large proportion of sulphuric acid should be necessary to ensure good results. It seems evident, however, from the results I have just given, that the main r6Ze of the sulphuric acid in dyeing is to chemically change a portion of the wool and render it :apable of combining with the dye. What the nature i f this chemical change may be I think it would be hard to tell a t present, but 1 hope to be able to con- tinue our researches on this interesting and important 3ubject,and to report again on the results a t a future meeting of this Society.