326 Dr. Thomas Thomson on [May 



The Prussian-blue, to induce the blue colour so conspicu- 

 ous in the calico, is dissolved in perchloride of tin, which is 

 prepared by passing a current of chlorine gas through a 

 solution of protochloride of tin. The solution is then 

 diluted with water, in which tartaric acid is dissolved, in 

 the proportion of 4 lbs. to the gallon, and afterwards 

 thickened with starch or British gum. It is then ready for 

 use. When cloth on which this paste has been printed is 

 passed through the vat containing a solution of chloride of 

 lime, the oxide of tin is precipitated by the action of the 

 free lime upon the perchloride, and fixes the blue on the 

 cloth ; while, at the same time, the tartaric acid, by dis- 

 engaging chlorine from the chloride of lime, destroys the 

 red colour of the cloth. Hence, the blue shows, as blue 

 always does when deposited on a white ground. 



The yellow portions of the calico had been rendered white 

 in the way formerly described. The yellow was afterwards 

 induced by a decoction of Persian berries. When this 

 yellow die was deposited over the blue it formed the green 

 so conspicuous in the calico, and adding so much to its 

 beauty. 



8. Chrome Yellow on Indigo Blue. 



The mode of obtaining a white upon dark-blue has been 

 already described. To form a paste which shall at the same 

 time resist the blue vat and leave a mordant for yellow, a 

 solution of nitrate and acetate of lead, with nitrate and 

 acetate of copper, is formed and brought to the requisite 

 consistence with gum and pipeclay. While the indigo is 

 depositing itself upon the cloth, the lime which holds it in 



