or important, any real progress having been checked by the
World War, while in the rush to make up for loss of time post-war
developments have also been few and far between.
As far as cotton-dyeing is concerned the most striking feature was the continued demand for the fast colours produced by means of vat dyes (indanthrene dyes, thioindigo red, etc.) which were introduced prior to 1914. These colouring matters, of which a wide range is now available, are being extensively used, in spite of their high price, for dyeing casement cloths, warp or weft threads to form the pattern in " grey " or unbleached piece goods which are subsequently bleached in the piece, and for the pro- duction of the fastest class of work in calico printing. Effects are thus obtained, even in bright colours and tints, in a degree of fastness formerly unknown, and this circumstance should go far to strengthen public confidence in the permanence of high-class coloured cotton goods.
Of colouring matters produced on the fibre, aniline black ' is by far the most important, and is used in increasing quantity. This black may be produced on the fibre by different methods, but the one almost universally employed to-day is a modification of Light- foot's original process patented as long ago as 1863. Commercially known as a " copper black," it is obtained by impregnating the material with a liquor containing aniline salt, copper sulphate and chlorate of soda, and, after ageing at a moderate temperature, run- ning the goods through a hot dilute solution of bichromate of soda. This latter treatment constitutes the improvement on Lightfoot's process.
The production of insoluble azo dyes on the fibre, which was orig- inated by Holliday in 1880 and has since been improved upon, is largely employed especially for the brilliant para-nitraniline red, a colour which also lends itself to the production of cheap but very striking resist effects in calico printing. The substitution of the anilide of beta-oxynaphthoic acid (naphthol A.S.) for beta-naphthol in the " prepare " may be regarded as a distinct recent advance in this class of dyeing, for the resulting colours are not only fuller and more level but the new colouring matters are tinctorially about twice as strong as those obtained with beta-naphthol. A still further improvement has recently come about by which the number of operations required to produce the colour is reduced to padding and steaming. To this end the fabric is padded with a mixture of naph- thol A.S. and a nitrosamine (the nitrosamine obtained from diazo- tized ortho nitro para-toluidine) and the colour developed by steam- ing in a rapid ager. It appears likely that this class of colour will have considerable application in the future.
Among the direct cotton colours a complete range is now available (of the benzo fast red and other types) which yield shades of re- markable fastness to light, a property which was rarely shown by earlier representatives of this class of dye; For goods such as case- ment cloths this property is naturally an advantage, for the colours are not only easier to apply than the vat colours but are considerably cheaper. It should, however, be borne in mind that although they possess fastness to light they are liable to bleed in washing as badly as their predecessors.
Other improvements in cotton-dyeing relate mainly to labour- saving devices in the dyeing of yarn. Dyeing in the cop, " cheese " or on the beam (for warps) is more largely practised than formerly and various appliances are employed for the purpose. The principle in all of these is, however, the same, i.e. instead of the yarn being moved about in or passed through the dye liquor, the material to be dyed is held in situ and the dye liquor is caused to percolate evenly by pumping or other suitable contrivance. It is easy to understand that only such colouring matters as can be obtained in perfect solution can be employed for this kind of dyeing. The process re- quires skilful management to get good results, but if such can be achieved with certainty- it not only saves much labour but the yarn remains in a better condition. In hank dyeing and washing the turn- ing of the hanks to ensure uniformity of treatment requires much hand labour. This is now largely dispensed with by the use of suit- able machinery for the purpose.
As regards wool-dyeing no great changes have taken place in the ordinary run of bright and most fancy colours, which are mainly got with acid dyes. For blacks and browns and other sombre colours which were formerly dyed almost exclusively with mordant colours (and are still so dyed for the best class of work) , two classes of azo dyes have come into prominence which are rendered faster by means of chromate or bichromate of soda.
Diamond black may be taken as a type of the first class. The wool is dyed with this colour in the ordinary way in an acid (acetic) bath, and at the end of the operation bichromate of soda is added to the
1 Through an oversight the copper sulphate (10 parts) was omitted in the recipe given in 8.751. The total volume of the liquor (200 parts) should also have been stated.
bath and the boiling continued for some time, this additional treat- ment resulting in a considerable improvement in fastness and at the same time darkening the shade. Colouring matters of this type are known in the trade as " after-chrome " colours. The other class comprises the " meta-chrome " colours, and of these meta-chrome brown may be taken as typical. The dye-bath is made up with colour- ing matter, chromate of soda and ammonium sulphate. When the temperature of the bath approaches the boil ammonia is given off and the bath gradually becomes acid, causing both colouring matter and some of the chromium to be taken up by the fibre.
As in the case of cotton, machine-dyeing is now largely practised in dealing with wool in the loose state, in slubbing and in yarn. Here also a considerable saving in labour is effected and the valuable qualities of the fibre are much better preserved.
As far as silk -dyeing is concerned what changes have occurred are not of sufficient importance to merit special mention here. Artificial silk, especially that obtained from viscose which comes into the market in ever-increasing quantity, is dyed like cotton, but requires more care in manipulation since in the wet condition its tensile strength is considerably diminished.
Effects of the War. During the years preceding 1914 Great Britain had been drawing roughly nine-tenths of its require- ments in coal-tar dyestuffs (about 18,000 tons valued at 2,000,000 annually) from abroad mainly from Germany. It was therefore clear at the outbreak of war that, unless the deficiency could be made up the British trade in coloured textiles would be severely handicapped as soon as the stocks in hand were exhausted. As early as Sept. 1914 a strong committee of British chemical manufacturers, colour manufacturers and colour users, styled " The Dyewares Supply Enquiry Committee," was inaugurated in Manchester under the auspices of the Society of Dyers and Colourists to discuss ways and means to meet the situation. This committee held numerous meetings at which various recommen- dations were made, some of which were ultimately taken up by the Board of Trade. The cardinal point which it was sought to elucidate from the start was the wants of the colour users, and to this end it was sought to make a classification of the imports before suggesting any definite course of action. The users were therefore appealed to, but although the majority readily re- sponded several large users, including two of the large combines, refused to cooperate and the whole scheme fell through. The list, which would have been of great use and would not have taken long to compile, was completed and published at the instance of the Board of Trade five years later. In the meantime, stocks had long since become exhausted, and in spite of the enormously increased activity of the English colour makers and of the timely assistance of the Swiss colour works, 2 the supply was nothing like equal to the demand. The enormous profits realized by makers were largely devoted to extending and improving their works, but the prices of dyestuffs both artificial and natural nevertheless soared to unheard-of figures. The shortage of dyestuffs was brought home to the public by the miserable quality of the colours in wearing apparel offered for sale. Khaki for the army was dyed on wool mainly with a colouring matter of the meta-chrome series, whereas for cotton the old method (in which chromium and iron salts supply the colour without the use of any dyestuff) was available, but khaki shades were also dyed largely with sulphide colours. Indigo for navy clothing was not available in sufficient amount to go round, and its place was taken on wool by an azo dye known as coomassie blue. For indigo-blue shades on cotton sulphide blues were mainly employed.
The principal makers of coal-tar colours in England in 1914 included the following firms: Ivan Levinstein & Co., Blackley, Manchester; Read Holliday & Co., Huddersfield; Claus & Co., Droylsden; The Clayton Aniline Co., Manchester (owned by a Basle firm and mainly concerned with intermediates); The British Alizarine Co. of Silvertown; a works at Bromborough owned by a combine of three German colour works, and a works at EUesmere Port owned by another German combine. The two latter were sequestrated by the Board of Trade and subsequently disposed of
2 Seeing that the Swiss colour makers were likely to help the British textile industry out of their dilemma, the German Govern- ment stopped supplies of raw materials to Switzerland, and these were sent from England on the understanding that an equivalent supply of dyestuffs should be delivered.
