378 The Art of Dyeing. 



salt of soap combines with the colouring matter upon the 

 calico when the dyed cloth is passed through warm or hot 

 soap-suds, and renders the colour darker. At the same 

 time, some oil, or fat, goes to the mordant, by which most 

 colours acquire more permanence. The great durability of 

 Turkey-red, in the manufacture of which olive-oil is em- 

 ployed, is to be ascribed to this cause. 



In clearing the dyes by soap-suds, care must be taken not 

 to dissolve the soap in water containing lime, otherwise a 

 combination of soap and lime is formed, which is deposited 

 on the cloth, in the form of a fine white powder, rendering 

 it ugly, and injuring it. 



If no water but such as contains lime can be had, the 

 objection mentioned may be removed by boiling the solu- 

 tion, and skimming off the combination of lime and soap 

 from the surface. 



Soap-suds are also employed to cleanse white grounds, 

 where the property of the soap-suds already mentioned is 

 exhibited, of making many colours more permanent. 



If we take two pieces of mordanted cotton, boil them 

 both in the same solution of madder and wash them ; they 

 have both acquired a reddish colour. If one of these pieces 

 is passed through hot soap-suds— well washed and laid with 

 the other piece on the grass to bleach — it will be found that 

 one of them will be bleached completely white, the other, 

 on the contrary, much slower. The last, is that which has 

 been passed through the soap. 



Hence, it follows, that madder colours on a white ground 

 should not be passed through soap-suds before the bleach- 

 ing is completed. In this case, a bran bath may be em- 

 ployed with advantage, instead of the soap-suds. 



From the beneficial action of oil in rendering the colour 

 of Turkey-red permanent, it might be concluded, that the 

 process of passing the mordanted calico through soap-suds 

 before dyeing it with madder, would be beneficial, as also 

 in this case, a combination is formed with the oil, mordant 

 and cotton. The dye, however, is not improved. It 

 appears faint, and can be scraped off even when carefully 

 dyed with madder. This shews, that in the Turkey-red, 

 the oil exists on the calico in quite a different state from 

 that which it possesses, in the case of the soap. 



