DYEING. 



239 



tit' Stuffs, exposed to the operations of aluming and galling. In 

 v ' "Y" < " r ' the preparation with alum, about four ounces of it are 

 Alumine required to each pound of stuff. Some add a solution 

 and galling, of soda, in the proportion of 1-lGth of the alum; others, 

 ' a small quantity of tartar and arsenic. The cotton is 

 thoroughly impregnated with this solution, by working 

 it in small quantities ; it is then put altogether into a 

 vessel, and what remains of the liquor is poured over 

 it. In this state, it is left for twenty-four hours, and 

 then carried to a stream of water, where it is allowed 

 to remain an hour and a half, or two hours, to remove 

 the superfluous alum ; after which it is washed. In 

 the operation of galling, different quantities of galls 

 are employed, according to the quantity of astringents, 

 and the effect desired. The galls powdered are boiled 

 for about two hours, in a quantity of water proportion- 

 * ' ed to that of the cotton to be galled. The liquor is 

 then suffered to cool to a temperature which the hand 

 can bear, after which the stuff is divided into a num- 

 ber of equal parts, that it may be wrought pound by 

 pound, and what remains after the operation, is poured 

 upon the whole together, as in the process of aluming, 

 already described. It is then left for twenty-four hours, 

 especially when intended to be maddered for black ; 

 but for other colours, twelve or fifteen hours are suffi- 

 cient. When stuffs are galled, which have already re- 

 ceived a colour, the operation must be performed in 

 the cold, that the colour may not be injured. See COT- 

 TO.V. 



CHAP. V. Of Flax. 



200. As we wish to describe, at present, only those 

 properties of stuffs which are immediately connected 

 with dyeing, and as in this respect flax so nearly re- 

 sembles cotton, that to prepare it for the reception of 

 the dye, it must undergo tfie very same operations we 

 shall refer the reader, for the other properties of flax, 

 to the articles FLAX and LINEN. Hemp is also treated 

 in the same manner as cotton, so far as relates to dye- 

 ing. See HEMP. 



SECTION IV. 

 OF MORDANTS. 



General 20 '- THE colouring particles seldom have such a de- 



ricwofthc cided affinity for the substances usually submitted to 

 nature of the operations of dyeing, as to form with them a per- 

 nordanti, inanent union ; it frequently happens, indeed, that the 

 same solvent which deposits the colouring matter on 

 the stuff, will, with equal facility, re-dissolve and erase 

 it. We have already stated, however, that the colour- 

 ing matters possess very strong attractions for c.irths 

 metallic oxides, particularly for the earth of alumine 

 .uid the oxides of iron ; and as these bodies also unite 

 re.idily with the fibre* of which stuffs are usually fabri- 

 cated, a triple compound may thus be formed, consist- 

 ing of the stuff, the colouring matter, and the chemi- 

 cal agent having an attraction for Iwth. The substan- 

 hi< Ii -orvt- a> a Ixind of union between the colour- 

 ing matter and the stuff, are called mordants, a term 

 applied to them from the mechanical action which they 

 were suppled to exert upon the latter, to prepare it 

 for the reception of the dye. As the theory cunci-rn- 

 ing the action of mordants, which first MggMtod the 

 term, is now completely exploded, Mr Henry has pro- 

 posed to substitute in place of mordant, the word basis. 



We shall sometimes employ the one term, and some- 

 times the other. 



202. The word mordant is also applied in a more ex- 

 tensive sense, not only to denote those substances which 

 promote the union of the colouring matter with the 

 cloth, and render that union permanent, but all those 

 agents which affect, in any respect, the colouring mat- 

 ter in its new state of combination. Dr Bancroft has 

 proposed to apply the term alterants to this class of bo- 

 dies, their object being not so much to fix, as to vary 

 and modify the shades of adjective colouring matters. 



203. The nature of mordants deserves to be investi- 

 gated with the utmost attention, for though almost all 

 the substances included under this appellation have been 

 discovered by accident, an accurate analysis of their ac- 

 tion must tend greatly to improve the principles of dye- 

 ing, and give something like a scientific form to its pro- 

 cesses. 



204. A mordant is not always a simple agent ; new 

 combinations are sometimes formed by the ingredients 

 of which it is composed,so that the substances employed 

 are not the immediate agents, but the compounds to 

 which they give rise. " The substances which com- 

 pose a mordant, are sometimes incapable," says Ber- 

 thollet, " of decomposing each other so\ely by their own 

 attractions ; but the attraction of the stuff for one of 

 their constituent parts brings about a decomposition 

 and new combinations, and sometimes this effect is not 

 produced or completed without the aid of the attraction 

 of the colouring particles. This appears to be the case 

 in the mixture of alum and tartar, one of the most com- 

 mon mordants employed in the dyeing of wool." 



205. " I dissolve," continues he, " equal weights of 

 alum and tartar ; the latter salt, by this mixture, acqui- 

 red a greater degree of solubility than it naturally pos- 

 sesses, but by evaporation and a second crystallization, 

 the alum and the tartar were separated, so that they had 

 not decomposed each other. 1 boiled for an hour half 

 an ounce of alum with an ounce of wool, a precipitate 

 was formed, which 1 washed carefully ; it consisted 

 chiefly of small filaments of wool incrusted with earth ; 

 to this I added sulphuric acid, and evaporated to dry- 

 ness, dissolved it, and obtained crystals of alum. Some 

 carbonaceous particles separated from it. I evapora- 

 ted the liquor in which the wool had been boiled, but 

 obtained from it only a few grains of alum ; the remain- 

 der would not crystallize. I re-dissolved it, and pre- 

 cipitated the alumine by an alkali : the precipitate was 

 of a slate colour ; it grew black upon a red hot coal, and 

 emitted alkaline vapours. 



" By this experiment," says he, " we see that the wool 

 had decomposed the alum ; that a part of the alumine 

 had combined with its most detached filaments, which 

 were least retained by the force of aggregation ; that a 

 part of its animal substance had been dissolved and pre- 

 cipitated by the alkali, from the triple combination 

 which it had formed. I made the same experiment 

 with half an ounce of alum, and two drams of tartar ; no 

 precipitation took place. I obtained by evaporation a 

 small portion of the tartar, and some very irregular 

 crystals of alum, the rest would not crystallize ; this 

 I diluted with water precipitated by potash, and ob- 

 tained by evaporation a salt which burned like tartar." 

 He afterwards infers from the whole, " that the wool 

 had begun a decomposition of the alum, that it had 

 united with a part of the alumine, and that even the part 

 of alum which retained its alumine had dissolved some 

 of the animal matter ; that the tartar and alum, which 



Of Mor- 

 dants. 



Alterants. 



Mordants 

 do not al- 

 ways act by 

 their im- 

 mediate 

 agency. 



Mutual 

 action of 

 the mor- 

 dants and 

 the stuffs. 



