IN THE DYEING OF WORSTED AND SILK. 



161 



A circumstance which is in favour of the possibility of 

 fixing this colouring matter on fabrics in a state of indigotine 

 is, that some organic substances (such as sulpho-vinic acid, 

 sulpho-glyceric acid, and other sulpho-acids) possess the pro- 

 perty of being decomposed and resolving themselves into their 

 primitive constituents by a simple ebullition in water. 



This red sulphate of indigo may be ranked in that type of 

 organic bodies, where it figures under the name of Sulpho- 

 purpuric Acid. As it ought to partake of the properties of 

 the series of compounds mentioned, it should necessarily, on 

 its ebullition in water, decompose itself into free indigo on 

 one side, and into free sulphuric acid on the other. Conse- 

 quently I presumed that by introducing fabrics into the vessel 

 where the process was going on, and at the moment of the 

 separation of the colouring matter, I could fix this colour 

 upon the fabrics so introduced. 



But the first experiment I made did not turn out to be 

 satisfactory. Cotton remained untouched by the colour, whilst 

 the worsted took off and successfully retained the colouring 

 matter. I made three consecutive trials on the occasion ; the 

 first in a neutral bath, the second in an acid bath, and the 

 third in an alkaline one ; but in all the three cases, so far 

 as the cotton was concerned, there was no successful result. 

 Hence it appears that the cotton has no affinity for this 

 indigo. But silk and worsted may be efiectually dyed in the 

 way I have indicated, if the bath be only kept acid. 



As I have already observed, some of these patterns imitate 

 the Prussian blue, and those washed in soap or alkaline water 

 resemble the purple produced from logwood and cudbear, 

 which shades could not, up to the present time, be pro- 

 duced by the employment of indigo alone. 



A question which it will now be worth while particularly 

 to inquire into is this — whether the indigo appears on these 

 fabrics as indigotine, or as sulpho-purpuric acid, or as a 

 modification of this acid. 



Y 



