SECT. m. NECESSITY FOR MORDANTS. 125 



madder dyes most extensively employed are alizarine 

 and flower of madder. Mauve and other dyes are 

 derived from guano, the offal of seabirds, which is 

 imported in large quantities for manure. 



The coal tar colours are manufactured on a highly 

 scientific plan and most extensive scale in Great Britain, 

 to supply the enormous quantity annually consumed in 

 dyeing silk and printing cotton. In general, animal 

 substances such as silk and wool can be permanently 

 dyed at once, because they have a strong affinity or 

 attraction for coloured dyes. If silk is destined to be a 

 moire, the silk before it is woven undergoes a chemical 

 process in order to introduce fatty matter into it which 

 gives a softness to the silk when woven and renders it 

 fit to receive the moire by intense pressure. 



Cotton cloth has no affinity for dyes, which are 

 washed out at once if not fixed by art, because cotton 

 fibre consists of minute tubes generally open at the,, 

 extremity, which imbibe the dye by capillary attraction, / 

 but cannot retain it unless fixed by a mordant, such as 

 the white of a raw egg, which readily absorbs any dye 

 that is mixed with it, and being then laid on the cloth 

 in any pattern it is absorbed by the tubular fibres, and 

 when coagulated by steam or any other application of 

 heat it is immovably fixed. Both animal and vegetable 

 substances afford a variety of mordants. Caseine or 

 cheese, the curd of milk, which may also be obtained 

 from pease and beans, is the mordant most used by 

 calico printers ; for if caseine be dissolved in twice the 

 quantity of alkali necessary for its solution, it coagulates 

 like white of egg and may be used in the same manner. 

 Skimmed milk cheese from Scotland and Holland when 

 purified is extensively used in calico printing. The 

 quantity of mordants required is very great, for of all 

 the cotton that was imported into Britain before the late 

 American civil war, one seventh only was manufactured 



