430> OUR COAL-TAR DYES. 



These colouring matters, it will be admitted, are a fruitful result of 

 chemistry on refuse matter, so disagreeable, so uninviting, and apparently 

 so little adapted for decoration as coal tar ; but the list by no means ends 

 here, matters possessing innumerable variety of colour are attained from 

 Naphthaline and the other constituents of coal tar, some of which admit of 

 useful application, whilst others are capable of no practical use, either from 

 inferiority of tint or deficiency in permanence, but as this branch of 

 chemical science advances, useless as they now seem, they may rival mauve 

 and magenta. In the hands of the dyer, these colouring matters require no 

 complex processes to effect their transfer to silk or wool, in fact, it would 

 seem that the fibres of these fabrics possess a most powerful affinity for the 

 colouring matter, and take it up so perfectly that the liquid in which they 

 have been dyed is left colourless. 



The process is thus : — A solution of the mauve, roseine, &c, in spirits of 

 wine is mixed with hot water, previously acidulated with tartaric or oxalic 

 acid, and then diluted with cold water ; in this mixture the fabric is 

 worked until it acquires the required shade. With some other of these 

 colouring matters the proceeding is still more simple, a cold watery solu- 

 tion of the material being alone necessary to form the bath. Small bottles of 

 these dyes are now sold by druggists, and by dilution with water, form a solu- 

 tion, so that ladies (if they are regardless of staining their figures) may become 

 their own dyers. Thus, then, with regard to silk and wool, these colours 

 are substantive, that is, white with the fibre without the aid of any second 

 substance or mordaunt, as they are called. But this is not the case with 

 cotton ; with this material the colours are not " fast " without a mordaunt. 

 The process which is adopted to fulfil this object is interesting from dis- 

 playing the application of a property possessed by these dyes which might 

 at first seem to be of minor importance. Mr. Perkins discovered that the 

 colouring matters of tar formed insoluble compounds with tannic acid, 

 which exists largely in gall nuts ; this property, coupled with a metallic base 

 in the fibre, he made the basis of his mordaunt. Practically it is effected 

 by soaking the cotton in a decoction of galls, and then in a solution of tin 

 salt (stannate of soda), after wringing out in an acid liquor and washing, it 

 is immersed in a bath of the colouring matter. A similar plan is adopted 

 in printing, the pattern is impressed on the cloth with tannic acid, on a 

 surface prepared with the tin, and on being immersed in the dye, that 

 portion retains the colour. 



Of the numerous pigments yielded by the refuse matter of gas-water, 

 Mr. Perkins says that there are only four which are used extensively by the 

 dyer — namely, mauve, magenta, picric acid, and azaline, a beautiful blue 

 prepared recently by a Parisian chemist, who has not made his method 

 known. Of these, the first resists the action of light best, and patents are 

 being taken out almost daily for the purpose of giving greater permanency 

 to these colours. 



Such are a few of the wonderful results of the magic of chemistry on the 

 refuse matter of gas works, serving to show that that which is apparently 

 worthless may, by the application of science_, be made most valuable in truly 



