244 



DYEING. 



or MO 



Attraction 

 of utrin- 



i;cnu for 

 sluftj. 



mw of the 

 effect* of 

 monUon. 



Rulphate were exactly known. They first estimated 

 the quantity of the astringent principle by the quantity 

 of sulphate which each liquor could decompose, and af- 

 terwards by the wright of the black precipitate which 

 was formed. To saturate die decoction of two ounces 

 of pills, three drains and sixty one grains of sulphate 

 of iron were required, and tin- prei ipit.it.-, wlu-n col- 

 lected and dried, weighed seven drams twenty four 

 grains. The decoction of oak bark it of a deep yel- 

 low ; a very small portion of sulphate of iron gives it 

 a dirty reddish colour, and a larger one changes it into 

 a deep brown. The quantity of sulphate required to 

 saturate the decoction of two ounces of this bark was 

 eighteen grains, and the precipitate, when collected and 

 dned, weighed twenty-two grains. The inner bark of 

 the oak afforded very nearly the same result. The de- 

 coction of the raspings of the heart of oak required 

 for its saturation one drachm twenty four grains, and 

 the precipitate obtained was of the same weight. The 

 decoction of the external wood of the oak produced very 

 little precipitate. The decoction of sumach acquired a 

 reddish violet colour when a small quantity of the sul- 

 phate of iron was added. The quantity required for 

 its saturation was two drachms, eighteen grains. The 

 decoction of logwood became of a sapphire blue colour 

 by the addition of sulphate of iron ; beyond the point 

 of saturation the blue becomes greenish and dirty. The 

 exact quantity required for saturation was one drachm, 

 forty eight grains, and the weight of the precipitate 

 was two drachms, twelve grains. All the precipita- 

 tions in which the oak was used took place readily ; 

 that by logwood a little more difficultly, but still more 

 easily than that of galls. These eminent chemists af- 

 terwards ascertained, that the quantity of astringent 

 substances required to give a black colour of equal in- 

 tensity, to an equal weight of the same doth, was pro- 

 portional to the quantities of astringent principle which 

 had been estimated in each kind by the foregoing ex- 

 jreriments ; but the black obtained by means of the dif- 

 i'erent parts of the oak, did not resist proofs or tests 

 go well as that produced by galls. It appeared also, 

 that logwood alone was incapable of producing so in- 

 tense a black as galls or oak, nor was the colour so per- 

 manent. 



233. Having thus examined the properties of the as- 

 tringent principle, with respect to its affinities with so- 

 lutions of iron, it ought also to be considered witli re- 

 spect to its affinities with stuffs, since its action as a 

 mordant must depend upon its attraction to the latter 

 as well HS to colouring matters. Silk acquires by gall- 

 ing, which consists in macerating a stuff' in a decoction 

 f galls, an addition to its weight which cannot be ta- 

 ken from it again, beyond a certain, by repeated wash- 

 ings ; after which operation, the stuff, when put into a 

 solution of iron, is dyed black, because the astringent 

 principle, decomposing the sulphate of iron, forms a 

 triple compound with the oxide of iron and the stuff. 



234. A galled stuff is also capable of combining with 

 wther colouring particles, the colours of which thereby 

 acquire fixity, if they do not naturally possess it, so 

 that the astringent communicates its durability to the 

 triple compound, or perhaps the more complex one 

 which is formed, but the colour is commonly rendered 

 deeper by this union. 



235. As the mordants and colouring particles have a 

 mutual action upon each other, the nature of the latter 

 is often so much altered by their union, that by vary- 

 ing the mordants, we may multiply prodigiously the 

 shades of colour obtained from the came colouring mat- 



ter. This may be done by simply varying the mode 

 of their application : thus we shall obtain clitlcrcnt ft- 

 fects by impregnating the stuff with the mordant, or 

 by mixing the mordant with the bath, by applying heat, 

 or using repeated exsiccations. The greater or less dis- 

 position of the stuff to unite with the colouring matter, 

 gives rise to considerable differences in the mode of ap- 

 plying the mordant. If the attraction of the colouring 

 matter to the stuff be strong, the mordant may be 

 mixed with the colouring matter, and in this state 'lx>th 

 may be presented at once to the stuff; but if it be 

 weak, the compound formed by the mordant and co- 

 louring matter might, in this way, bo precipitated in 

 the bath without attaching itself to the stuff; and to 

 prevent this inconvenience, the stuff must first bt im- 

 pregnated with the mordant, and afterwards exixi.sed 

 to the colouring matter. In tile dyeing of some colours, 

 it is necessary to employ one mordant for the ttuff, 

 and another for the colouring principle. 



SECTION V. 



OF THE PROCESSES OF DYEI.NC.'. 



CHAP. I. 



General View of the Practical Operations of Dyeing. 



236. In order that a dyeing manufactory may be Dyeing 

 conducted in the most advantageous manner, Berthol- house.-:. 

 let remarks, it ought to be upon an extensive scale ; 



the subdivision of labour affording an opportunity for 

 each workman, by his attention being directed exclu- 

 sively to one object, of acquiring dexterity and perfec- 

 tion of execution, while the whole operations are ma- 

 naged in a connected manner, and carried on in detail 

 without loss of time. To these considerations it may 

 be added, that a variety of materials, which, in a small 

 establishment, would be rejected as useless, may often 

 be applied with the utmost success to a different 

 operation. Thus a bath which has been too much 

 weakened for a particular colour, or even for the light- 

 er shades of that colour, may frequently be found ser- 

 viceable, by affording a ground for other stuffs, or form- 

 ing a new bath by the addition of fresh ingredients. 



237. A dye-house should be spacious, well lighted, situntiou 

 and placed in a situation to command an easy and abun- and ron- 

 dant supply of a stream of good water. The floor ought 



to be well paved, and proper gutters formed for carry- 

 ing off dirty water and spent baths. In short, every 

 thing should be constructed with a due regard to clean- 

 liness, both on account of the health of the workmen, 

 and the better performance of the different manipula- 

 tions. Drying houses should be built in exposed situ- 

 ations, and constructed in such a manner as to exclude 

 the rays of light, while they admit a free current of 

 air. 



238. The caldrons, the size and position of which 

 are to be regulated by the operations for which they 

 are designed, should be made of brass or copper, un- 

 less for dyeing scarlet, in the preparation of which it is 

 better to use tin vessels, as well as for other delicate 

 colours in which a solution of tin is employed. Brass 

 is preferable to copper, as it is less liable to be acted 

 upon by saline substances, and thus to spot the stuffs. 

 Vessels of a very large size should be furnished with 

 stop-cocks at the bottom to empty them when necessa- 

 ry ; and some contrivance should be employed above 



