1835.] Calico-Printing. 325 



those parts of it on which the tartaric acid had been de- 

 posited, are deprived of their colour, while at the same time 

 the oxide of lead detaches itself from its acid and becomes 

 fixed upon the cloth. The cloth, after being washed in 

 water, is passed through a solution of bichromate of potash, 

 which converts the oxide of lead into chromate, and thus 

 communicates the beautiful and permanent yellow colour. 



7. Blue and Black upon Turkey -Red. 



The mode of discharging the colour from Turkey-red 

 cloth has been already explained, and also the mode of 

 impregnating the white spots thus formed with chrome 

 yellow. At present we shall endeavour to explain how the 

 black, the blue, and the green, which add so much to the 

 beauty of the calico here presented to the reader, are induced. 



To obtain the black a perchloride of iron is prepared, 

 by dissolving carbonate of iron in muriatic acid. This 

 solution is afterwards employed for dissolving Prussian- 

 blue, which it does very well, provided the blue be ground 

 into a fine powder. The solution is afterwards diluted with 

 water, and brought to the proper consistency by mixing it 

 up with starch, and keeping it for some time at the tempera- 

 ture of 200°. The paste thus made, when cooled down is 

 fit for use. It is applied to or printed on the cloth at the 

 same time with the blue, and with the acid which is to pro- 

 duce the white observable on a portion of the cloth. The 

 cloth being passed through a solution of chloride of lime, 

 the free lime precipitates oxide of iron upon the Prussian- 

 blue, which assumes a black colour, because it has been 

 superinduced upon the red. 



