1835.] Calico-Printing. 323 



The portion of calico here presented to the reader 

 exhibits specimens of no fewer than four different chemical 

 colours : namely, pink, blue, green and orange. I shall 

 endeavour to explain how these different colours are 

 obtained. 



2. Chemical Pink. — This beautiful colour is produced 

 either from Brazil or peachwood. A decoction is formed of 

 these woods, which is thickened with gum-senegal, and 

 afterwards mixed with perchloride of tin. The salt preci- 

 pitates the colouring matter in the state of a lake, which is 

 re-dissolved by an excess of the salt of tin. In this state 

 of solution it is applied to the cloth, which in the course of 

 a few hours decomposes it, and when the cloth is washed, 

 the lake remains attached to it. 



3. Steam Blue. — It is known that when hydro-ferro- 

 cyanic acid is boiled in water, hydro-cyanic acid is evolved, 

 and a white powder precipitates which becomes Prussian- 

 blue by exposure to the atmosphere. It is in this way that 

 what is called steam-blue is produced. Crystallized prussiate 

 of potash is dissolved in water, and mixed with tartaric acid. 

 Bitartrate of potash or cream of tartar precipitates, and the 

 remaining liquid consists partly of hydro-cyanic acid dis- 

 solved in water ; but it contains also ' the white Prussian- 

 blue, if such an expression may be permitted. This liquid 

 is thickened with gum and printed on the cloth. 



Or sometimes gum-senegal is dissolved in aqueous prus- 

 siate of potash, and an equivalent of sulphuric acid added. 



The print is now exposed to the steam of boiling water, 

 and the blue raised* (if the other colours will allow) in a 



* The technical term for increasing the intensity of a colour. 



y2 



