312 WHITTAK.ER-i21GHT FASTNESS OF DYES ON VEGETABLE FIBRES” Wept. 1935

increased soaping. Beanand Rowe had suggested that long soaping of azoic dyeings, particularly under abnormally stringent conditions, induced large particles of the crystallised dyes to form on the surface of the goods, thus increasing the rubbing fault.

The Lecturer said that, in practice, it was not as easy to over-soap piece goods as yarn. The effect could be produced in the laboratory and depended largely upon the particular com- bination employed and the depth of shade.

M i . G. S. Marr asked whether the dyeings obtained by light soaping were suitable for commercial kier- boiling without the develop- ment of marking-off faults ?

The Lecturer suggested that most of the dyeings he had mentioned were suitable for use in open kiers with boiling soda ash solution. In practice, a considerable amount of dyed yarn for the towelling trade was given only a light rinsing and soaping treatment.

Mr. H. A. Turner asked if the relative fast- nesses to hypochlorite were approximately the same it‘ the pH of the hypochlorite solution was represented merely by the alkali present in the ordinary commercial hypochlorite diluted to give a pH of 8-10 ? If a more active hypo- chlorite of about pH 6-8 was used, would it not be found that the fastnesses in the more alkaline hypochlorite would be a combination of fastness to oxidation and probably fastness to alkali, whereas neutral hypochlorite solutions would give fastness to oxidation only 1

The Lecturer said that he had not done any work in connexion with the varying conditions of the hypochlorite treatment, but agreed with the remarks of Mr. Turner.

Some Comments on the Classification of the Light Fastness of Dyea on Vegetable Fibres

By C. M. WHITTAKER, B.Sc. Those members who take an interest in the

light fastness of colours will be aware that this Society and the corresponding German and American Societies have all published light fastness standards, and i t is hoped that these will be amalgamated eventually into a single series of internationally accepted standards. .

It is not intended to discuss these standards as standards, but a practice which, in the present author’s opinion, constitutes a misuse of these standards in the classification of the light fastness of dyes is worthy of serious consideration. The present author has ventilated the matter previously, both privately and pub- licly, and there is reason to believe that the criticism wi l l be met eventually, in one quarter at any rate.

The criticism may be stated very briefly as follows-The standards of light fastness me for specified depths of shade of dyes dyed under specified conditions; the standards are not the dyes themselves, but specified percentages of

the dyes. If a shade is classified by a light fastness number, it means that i t is equal in fastness to the depth of shade laid down as the standard for that particular light fastness number. Since no dye is equally fast in varying depths of shade, it follows, therefore, that no dye may be accurately classified in one class, yet it is found that dyes are classified repeatedly as, e.g. 6, 7, or 8. Such a classification is cluarly incorrect, and the present author desires to state most emphatically that such a practice is a misuse of the light fastness classification schemes. Since i t is no use putting forward destructive criticism without a remedy, it may be said a t once that there is an extremely simple remedy; it is only necessary to state the mini- mum percentage of the dye which it is claimed is equal in fastness to light to the standard pattern (a dyeing of this minimum percentage could easily be included on the pattern card itself for reference).

The practice of the present author in all recent tests on the fastness of dyes to light, is to dye up a range of eight shades of each single dye and mount them on cards. It is a useful method, because in a series of joint exposures the relative fastness of a number of dyes can be judged quickly. For instance, if a +yo dyeing of one dye has faded no more than a 18% dyeing of another dye, i t is possible very quickly to classify dyes in their order of relative fastness to light.

In 1933, a very wide clelection of 70 of the fastest-to-light direct cotton dyes wax exposed a t Droylsden. Each dye was exposed in eight depths of shade on viscose rayon and cotton yarns. This work alone required 1,120 dycings and a careful checking and mounting of 140 cards, for the supervision of which thanks are given to C. C. Wilcock. The patterns were exposed during April and May in ventilated glass cases facing due South at an angle of 45” on the mill roof a t Droylsden. The longest exposure took place from 8th April to 12th June, i.e. 65 days, during which period 227 sun hours were recorded on a Jordan sun recorder.

Theseresultswere astonishing and they enabled the present author to make the statement that there is nodirect cotton black,grey, blue, orgreen, available which is equal in fastness to light to the fastest-to-light dircct cotton reds, oranges, or yellows. This means that if the fastest-to- light direct cotton yellows, oranges, or reds are used in compound shades, there is no black, blue, or green of equal fastness to light which may be used for drabbing purposes. Conse- quently, when a dyer is compelled to use a black, blue, or green along with a fastest-to-light red, yellow, or orange, an unbalanced fade is sure to occur. Here is a gap for research workers to fill, and the present author has directed the attention of all the dye manufacturers to the problem which it is hoped will be solved ultimately to the satisfaction of all concerned.

Swt. 19351 WHITTAKER--“LIGHT FASTNESS OF DYES ON VEGETABLE FIBRES” 313

It is of interest to note that dyeings exposed a t 46” and horizontally suffered much more sevcrely than when exposed vertically, whilst side-by -side exposures of cotton and viscose rayon showed how much faster to light the same dye is on viscose than on cotton.

It follows from these remarks that the above fact could not have been discovered by taking into consideration the present method of classification of light fastness employed on dye manufacturers’ pattern cards, since direct blacks, blues, and grecns are classified with the same fastness numbers as direct yellows, reds, and oranges. If the minimum percentage of the dye which is equal to the light standard claimed wcre stated on the cards, however, in accordance with the present author’s suggestion, it would be possible by comparing these minimum per- centages to form an accurate measure of the relative fastness to light. The adoption of the suggested modification of the present method is worth careful consideration; the method would be easy to carry out, and in any case the relative fastnesses must be already known to those responsible for issuing the pattern cards.

(The Lecturer illustrated his remarks by exhibiting a series of pattern cards containing unnamed examples of the misuse of light-fastness standards.)

It iu frequently said that the fastest-to-light direct cotton dyes are almost as good as vat dyes; indeed the light-fastness numbers attached to some of them put them in the same grade as that assigned to vat dyetJ. It is possible actually to select a few direct cotton dyes, excluding blues, greys, and greens, which do make a very good showing on comparative exposures with vat dyeings, e.g. Chlorantine FttRt Yellow 3RLL, Chlorazol Fast Orange AG, Solophenyl Red Brown, and Solar Rubinole B give very good comparative results. (Exposure tests were ex- hibited.)

Further, it is not to be expected that if those dyes were used on casement cloths in full shades, the percentage of claims would be much higher than with vat-dyed goods. If a direct cotton grey, green, or blue has to be used for shading, howcver, the fastness to light of the dyeing is immediately lowered well below the fastness of a similar vat dyeing.

DISCUSSION The Chairman, Mr. L. G. Lawrie, agreed that

it was impossible to indicate the fastness of a dye simply by means of a number and without reference to the depth of shade and the method of dyeing.

M i . H. Brassard asked whether the tests would have given different results if made in a purer atmosphere than that of DroyIsden 2

The Lecturer said that very little differences were observed when similar tests were made in other districts. Every precaution had been taken in order to keep out dirt, and dyeings

which had been exposed for 200 days under glass were only very slightly soiled.

Mr. E. B. Adams said that customers some- times insisted upon the statement, fast to light, appearing on the invoice, whereas, according to technical experienoe, such a statement would be inaccurate.

The Lecturer said that a t Droylsden thcy absolutely refused to make such a statement. The firm with which he was associated not only refused to guarantee “fadeless” vat dyeings, but also “fadeless” direct cotton dyeings. If other firms would act similarly, the iiltimate cffeot would react favourably on the dyeing trade in Lancashire and Yorkshire.

Mr. J. R. Hannay said that the firm with which he was associated used the fastest dyes available, but they also would not give a guarantee of fadelessness. Plenty of dis- tributors would give such a guarantee on their own account.

Mr. G . M. Williams said that some dyes were definitely deleterious. Thus, a dye of liglit standard 6, when mixed with othcr dyes of similar fastness, might reduce the standard to less than 4. Such dyes should be labelled aH dangerous to use in mixtures. Many Pycrs were misled by using a standard of 6 or 7 without testing the fastness of the resultant dyeings. His firm also did not guarantee the fastness of a colour. He quite agreed that if dyers generally took up a similar stand, the industry would soon be placed upon a sounder footing.

The Lecturer said that if he had gone into the question of mixed shades he could havc spoken for much longer. Nigger browns wtm w r y good examples. They were the bugbear of thr cwnta- ment cloth trade, especially as thcy had to I)c dyed economically. It was of intcrctit to notc also that two Naphtols for an azoic brown were available; each of these when used alone gave an azoic shade of very good fastness to light, but immediately the two were combined in a colour complex, the result was that the dyeing faded.

Mr. D. F. Harrison referred to the superior light fastness of viscose rayon dyeings compared with cotton dyeings, and asked if this difference was due to the reflective surface in the former case absorbing less energy from the light rays ? Had any experiments been made in which a viscose rayon dyeing had been treated with an inert substance, e.g. barium sulphate, which would give a dull surface and would have no chemical effect on the dyeing during exposure ?

The Lecturer said that he had done no work on the lines indicated; he was not concerned very much with the theoretical explanation of the phenomenon mentioned.

Mr. G. S. Marr said that the difference observable in the degree of fading between dyeinga exposed a t an angle of 46” as contrasted with those exposed vertically was most remark- able. There was a much more drastic fading with awning than with rasenient cloths.

314 ROWE & ALLEN-“PROPERTIES O F m- AND p-AMINOAZO DERIVATIVES” IStpl. l93*5

The Lecturer agreed. All the experiments had been made a t an angle of 45”. Sun-umbrella and awning cloths, particularly when the latter were used a t the seaside, faded very badly. It had been calculated by one of his firm’s physicists that a fabric exposed a t an angle of 45” received double the amount of sunshine compared with that received by one ex osed vertically.

of the fastness properties of direct dyeings on viscose rayon and cotton represented results obtained with definite percentages of dyes, or whethcr the dyeings used were matched shades ?

(The Lecturer showed samples bearing m thie question.) He said that the cotton dyeings had been exposed for 10 days, and the viscose rayon dyeings for 63 days. There wa0 20% more dye on the viscose rayon than on the cotton.

Mr. E. Holden said that sometimes when dyes that were comparatively fugitive to light were mixed, the resultant shade was faster than either of the dyes used separately.

(The Committee of the Manchester Section desire to express their great appreciation of the help afforded by the General Electric Co. Ltd., in conmion with the arrangements for the above lecture. They are especially grateful to this firm for the. loan of m e of their Daylight Unit.u and for the way in which a suitable supply of A.C. current was obtained in place of the existing D.C. supply.)

Mr. E. Brown asked w i ether the comparisons

SCOlTISH SECTION Meeting held at the George Hotel, Buchanan

Street, Glasgow, on 12th April 1935, Mr. J. MUIR in the chair.

Preparation and Properties of m- and p-Aminoazo Derivatives of @-Naphthol

and of B-Hydrox ynaphthoic Arylamides F. M. ROWE, D.So., F.I.C., and R. L. M. ALLEN,

Ph.D. In the course of the investigation of the action

of boiling 0.36% aqueous caustic soda on cotton dyed with insoluble azo colours (this Jour., 1931, 47, 35,163; 1935, 51, 278), one of us found that the decomposition products of dyeings of Meta- nitroaniline Orange, Para Red, and diazothed Fast Red RL Base in conjunction with Naphtol AS-RL, include 3- and Q-aminobenzeneazo-~- naphthol, and 2-methyl-4-aminobenzeneazo-/?- hydroxynaphthoic - p - anisidide, respectively, formed from the original nitroazo colouring matters by the reducing action of cellulose and caustic soda.

The only aminoazo compound of this type previously described in the literature is 4-amino- benzeneazo-#?-naphthol which Meldola &st pre- pared as “a dull, bronzy uncrystallisable substance” by reducing Para Red in substance with ammonia and &mmonium sulphide (J.C.S., 1885, 47, 663). He diazotised i t and ooupled

with &naphthol, and a p-naphthol disulphonic acid, respectively, and described the former disazo compound as “a violet substance which crystallises from aniline in metallic green glisten- ing needles”, and the latter disazo compound as an acid dye which produces “fine indigo-blue shades that appear to be of great stability and fastness”. Subsequently, Meldola and E p o n (J.C.S., 1905,87,3) also prepared 4-aminobenz- eneazo-/I-naphthol by diazotising p-phenylene- diamine in presence of a large excess of sulphuric: acid, then converting into the insoluble diazo- chromate, and coupling with /?-naphthol.

Actually, aminoazo compounds of this type are most readily and conveniently prepared by reducing a fine suspension of the corresponding nitroazo compounds with sodium sulphide or hydrosulphide. Consequently, it appcared to be of interest to prepare a series of these aminoazo compounds in this way, and to examine their properties as dyes for cellulose acetate rayon. and as diazotisable basrs, or coupling com- ponents after condensation with 8-hydroxy- naphthoic acid, for use in the production of new types of insoluble disazo coloiiring matters on naphtholated cotton.

Twelve aminoazo compounds were prepared by coupling diazotisedm- andp-nitroaniline, 4-nitro- and 5-Ntro-2-aminotoluene, and 4-nitro- mid 5- nitro-2-aminoanisole, with p-naphthol and Naph- to1 AS, respectively, and a thirteenth by coupling diazotiscd 5-nitro-2-aminotoluene with Naphtol AS-RL. The resulting nitroazo compounds were f2ttred off, washed free from alkali with water, and the moist products reduced by heat- ing with aqueous sodium sulphide or hydro- sulphide solution on a steam-bath, or by boiling under reflux. Thus, six of the compounds con- tained the amino-group in the m-position with respect to the azo group and seven conttiirid the amino-group p - to the azo group. The aminoctzo compounds separated completely on cooling the reduction mixture and were filtered off, washrd well with water, dried, and crystallised from an organic solvent. The yield ( a ) given helow is that calculated on the quantity of bast. t akw for diazotisation in making the nitroazo compound, whilst for purposes of comparison the yield ( b ) is that obtained in a second experirnent in whidi ii h e suspension of the pure nitroazo compound was reduced. Compounds containing the nitro- group p - to the azo group are rccluced niorc. readily than the m-isomerides, and thc yivld could usually be improved in the forincr case by the use of the less alkaline sodium hydrosulphitlc in place of sodium sulphide. Loss in yield is accounted for by side-reactions and deconi posi - tion. In general, the alkalinity of the reduction mixture should be limited as far as possible; no more reducing agent should be used than is actually required; the temperature should be no higher than is necessary for rrduction; and heat- ing should be discontinued as soon a9 reduction is complete.