Ill 



DYEING. 





fl - ,.f 

 dyeing with 

 Sum blue. 



Prorenof 

 Macqucr. 



Another 



rroceaof 

 Holand dc 

 !.. Platriere. 



took much more slow ly, tlmn in the ordinary way of 

 .ii blue. Chapt.il remarks, that when the 

 sulphuric acid contains the smallest portion of nitric 

 .u'iil. the indigo assume* a greenish cast. 



353. When cloth is to be dyed of a Saxon blue, it 



is |m|MXed with alum and tartur; and a greater or a 



less uro|x>rtion of the solution H' indigo i- to be put into 



the bad i, according to the deepness of the required 



shade. The light shades may be given after the deep 



!>ut they liave greater lustre when they are dyed 



in a fresh bath, probably because the finer panic' 1 



the indigo are first attracted by the Mull'. For deep 



shades, it is best to employ the solution of indigo in 



-ive portions, raising the cloth on the winch. 



35*. In the history of colouring matters, (11'). ) we 

 alluded to the attempts which had been made to dye 

 cloth- by means of Prussian blue. We shall now de- 

 scribe some of the processes which have been proposed 

 for this purjwse. Two methods have been suggested 

 by M-iequer, neither of which can be said to IK- attend- 

 ed with the desired effect. In one he soaked the stuff's 

 in a solution of alum and sulphate of iron, and then in 

 a diluted prussiate of potash, containing an excess of 

 prussic acid ; and lastly, in water acidulated with sul- 

 phuric acid, to dissolve that portion of the oxide of iron 

 not combined with the prussic acid, which the uncom- 

 bined alkali had precipitated. By repeating successive- 

 ly these immersions, he at last obtained a fine blue, but 

 very unequal ; while the stuffs, by the action of the sul- 

 phuric acid and the alkali, had become harsh to the 

 touch. It is easy to see, that this process could not suc- 

 ceed. For, as Berthollet remarks, since an alkali not 

 saturated with prussic acid was used in the second im- 

 mersion, that part of the alkali which was not saturated 

 must dissolve more or less of the blue taken up in the 

 first. If any one, therefore, should repeat these experi- 

 ments, he ought to employ an alkali saturated with 

 prussic acid, or perhaps lime water, or rather magnesia, 

 both of which have the property of combining with 

 that acid. 



355. In Macquer's second process, the stuffs to be 

 dyed were boiled in a solution of alum and tartar, and 

 afterwards in water containing Prussian blue, diffused 

 through it in a finely powdered state. They were now 

 dyed uniformly, but the colour was faint, and seemed 

 merely to be united meclianically with the fibres of the 

 stuffs. 



356. M. Roland de la Platriere has published an ac- 

 count of another method of dyeing with Prussian blue, 

 which in many respects has a considerable resemblance 

 to Macquer's second process. On fine Prussian blue, 

 in the proportion of a pound to a piece of stuff, powder- 

 ed and passed through a very fine sieve, he poured in a 

 vessel of delft ware as much muriatic acid as reduced 

 it to the consistence of a syrup. The mixture, which 

 immediately began to ferment, was well stirred for 

 about .half an hour; it was then considerably diluted 

 with water, and stirred every hour for a day, till the 

 fermentation ceased, and the particles of the Prussian 

 blue, in a state of very minute division, were intimate- 

 ly united with the acid. Into a trough, narrower than 

 those usually employed, but widening more towards 

 the top, being two feet and a half high, two feet and a 

 half diameter at top, and two feet at bottom, seven or 

 eight buckets of water were poured for one piece of 

 stuff". The colouring composition, well diluted with 

 water in a separate vessel, was then added, by pouring 

 it into the bath through a very fine sieve. When the 



stiitl' was pl.iivd on the winch o\;-r the- trough, tlie r^ 

 bath was briskly ngitated, and nt the S.IIHC time the " f '' 

 stuff was let down quickly into the bath, and worked S """V"^ 

 as fast as possible tor two or three hour*. As the 

 Prussian blue is only in a state of mechanical solution, 

 the particles .ire very apt to be unequally deposited 

 upon the stuli', and it therefore requires the utino-,t 

 attention on the part of the workman to prevent this 

 taking place. He must work and rework tile stuff; 

 wash those parts which may have taken too deep a 

 shade in the bath itself; work it over again, now one 

 end first, then the other ; dry it ; work it again ; and 

 in short, use every means which his ingenuity can sug- 

 gest for rendering the colour uniform. The stuff should 

 always be washed and beetled between the dryings, and 

 in every dip introduced into the bath in a wet state. 

 After the proper colour has been obtained, it is dried 

 on the tenters in the open air, either in the sun or the 

 shade. 



357. Dr Bancroft has also proposed a method of Process of 

 dyeing with Prussian blue, which does not seem to Or B * - 

 labour under the disadvantages hitherto attending its crofu 

 use as a dye. By reflecting that the inequality of co- 

 lour to which the dyeing with this substance is liable, 

 was probably owing to the difficulty of applying the 

 ferruginous basis equally to all the fibres of the stuff", 

 he boiled up what he conceived to be suitable propor- 

 tions of sulphate of iron with quercitron bark, fustic, 

 and logwood, separately, (these vegetable dyeing drugs 

 having been chosen, not on account of their colours, but 

 their cheapness,) and applied the oxide of iron in this 

 state of combination to the cloth, which by this means 

 appeared to have imbibed it uniformly. He then im- 

 mersed it in warm diluted prussiate of potash, neutra- 

 lized by sulphuric acid, when the stuff became beauti- 

 fully blue ; and though he admits there were some in- 

 equalities in the colour of one of the pieces, he ascribed 

 it rather to his own want of attention to the proper 

 stirring and management of the dyeing liquor, and of 

 the cloth, than to any unavoidable difficulty in giving 

 evenness to the dye. The Prussian colouring matter 

 must be used in a moderate heat, otherwise it will be 

 precipitated by the sulphuric acid, and rendered unfit 

 for the purpose, unless dissolved again by potash, lime, 

 &c. 



358. The colour produced by these processes is one Qualities ,.r 

 of the most beautiful obtained in dyeing, and suffers no Prussian 

 change by exposure to the air in all its vicissitudes. bluc - 

 Holand de la Platriere left patterns of it in the open 



air for six months together. For a long time the colour 

 gained in vivacity, and at last lost but little. Acids 

 are not injurious to it ; and boiling with alum even 

 produces in it but little alteration. Dust, however, 

 and rubbing on the creases of it, soon tarnish it ; and 

 it is instantly affected by the slightest touch of an al- 

 kali. 



II. Processes for Dyeing Silk Blue. 



359. Silk is dyed blue, by employing the indigo vat Baik. 

 (348.) already described. Sometimes a larger pro- 

 portion of indigo is employed than is there directed, 



but nearly the same quantities of bran and madder. 

 Macquer states, that if half a pound of madder be em- 

 ployed for every pound of salt of tartar or potash, the 

 vat becomes greener, and its colour is more fixed in the 

 silk, without being of a less pleasing cast. The pastel 

 or woad vat is not used for dyeing silk, because it doc-; 

 not readily impart to it a sufficiency of colour. When 



