DYEING. 



performed in the cold, that the colour 

 may not be injured. Cotton, which has 

 been alumed, acquires more weight in 

 the galling than that which has not un- 

 dergone that process. Although alum 

 adheres but in small quantities to cotton, 

 it gives it a greater power of combining 

 both with the astringent principle, and 

 the colouring matter. 



Of Flax. 



As flax and hemp possess the same pro- 

 perties, as fur as relates to dyeing, the di- 

 rections for one will succeed equally well 

 for the other. 



Flux must undergo several prepara- 

 tions before it is fit to receive the dye ; 

 the first is the watering, by which the fi- 

 brous parts of the plant become dispos- 

 ed to separate, so as to be rendered tit for 

 spinning. 



In watering, a glutinous juice, which 

 holds the green colouring part of the 

 plant in solution, and which is the me- 

 dium of union between its cortical and 

 ligneous parts, undergoes a greater or 

 less degree of putrefaction, according to 

 the mode of conducting the operation. 

 This process is performed to the great- 

 est advantage in pits situated on the banks 

 of rivers, where the water may be chang- 

 ed often enough to prevent a degree of 

 putrefaction that would injure the flax, 

 and be prejudicial to the workmen, yet 

 not so often as to hinder the degree of 

 putrefaction necessary for rendering the 

 glutinous substance soluble in water. 

 After watering, the flax is dried, and the 

 ligneous parts separated by a mechanical 

 operation. 



Some have proposed the mixing a small 

 quantity of caustic alkali with the water, 

 to increase its solvent power, but it ap- 

 pears from Dr. Home's experiments, that 

 the alkali retards the operation, and ren- 

 ders the flax liable to break. But after 

 the watering and drying, alkaline sub- 

 stances dissolve the greatest part of the 

 colouring matter, on account of the 

 change it has undergone from the expo- 

 sure to air and light, and the consequent 

 absorption of oxygen. 



The processes published by the prince 

 of S. Sever, for obtaining fine dressed 

 hemp, depend on the solution of the co- 

 louring matter by alkali. He directs 

 that dressed hemp be lixiviated in a so- 

 lution of two parts soda and one of lime, 

 then impregnated with soap, and kept in 

 digestion ; and afterwards well washed 

 knd hackled; but in this process only 



that portion of the colouring matt 

 dissolved, which would have been carried 

 off by the first leys used in the beginning; 

 of the bleaching of the cloth. The 

 great fineness given to it probably can- 

 not be produced, but at the expense 

 of the length and firmness of the fila- 

 ments. 



A clergyman of the department of 

 Somme, in France, employs a process not 

 liable to the inconveniences caused by 

 leying the dressed hemp. He waters the 

 hemp as soon as it is pulled, and separates 

 the cortical part by a peculiar operation 

 immediately after the watering, and hav- 

 ing soaked it in a weak solution of black 

 soap, he washes it with great care ; pre- 

 vious to the drying, the colouring matter, 

 (which would afterwards have been so- 

 luble only in alkali) may be dissolved and 

 extracted by water, with the addition of 

 a small quantity of soap ; the hemp be- 

 comes much whiter, and divides better 

 and more minutely, without, however, - 

 having been injured ; and the leys pre- 

 paratory to the bleaching become unne- 

 cessary. Thread and linen contain then 

 a colouring substance, most of which may 

 be extracted by simple ley >, but there is 

 a part of it, which is really combined 

 with the vegetable fibres, and which can 

 only be taken away by the destruction of 

 its nature, effected by the combustion it 

 undergoes during its combination with 

 oxygen. Thread loses, by the operations 

 employed in bleaching, from one-fourth 

 to one-third of its weight. 



Flax, or linen, intended to be dyed, 

 must be subjected to the same operations 

 of scouring-, aluming, and galling, which 

 cotton undergoes. 



The well known greater difficulty with 

 which linen, cotton, and silk, take dyes 

 than wool, have been accounted for by 

 supposing the pores of their fibres to be 

 smaller ; this, however, appears not to 

 be true, from the greater quantity of co- 

 louring matter which they absorb. Un- 

 bleached cotton is always preferred for 

 dyeing Turkey red, because in this state 

 its colour is more permanent. The same 

 thing is observed of raw or unsecured 

 silk, which is found to combine more ea- 

 sily with the colouring matter, and to re- 

 ceive a more permanent colour in this 

 state, than after it has been scoured and 

 whitened. This has been accounted for 

 also on mechanical principles, but it more 

 probably is owing to the difference of 

 the affinity, which exists between the co- 

 louring matter and the substance separat- 

 ed from the silk or. cotton in bleaching or 



