160 MR. E. HAEFFELY ON THE USE OF SULPHO-PUBPURIC ACID 



honour of exhibiting for inspection some patterns, the re- 

 sults of the putting into operation of both processes, so 

 that the difference between the two may be fairly esti- 

 mated. I may be permitted to say that I have not the 

 least doubt that after a careful examination of these patterns, 

 every one will be inclined to give a preference to the blue 

 and purple colours obtained by the use of the red sulphate, 

 which has been introduced into commerce, and applied by 

 dyers with success, in some dyeing establishments of the 

 neighbouring county of York. 



I will now enter into a few details respecting the chemical 

 nature of these two sulphates. Upon an examination of the 

 formulae of the two chemical bodies referred to, it will be 

 found that the ordinary indigo extract is, properly speaking, 

 a hypo-sulphate of dehydrogenised indigo 

 = S^O'-h NC'-H^O', 



(The formula of the indigotine being — 

 NC'-H^O',) 

 whilst the red compound is a sulphate of indigotine — 

 SO\HO + N C'-H*0% 



Upon a comparison of these two formulae, it will be 

 remarked that in the case of the indigo extract, the indigo 

 and the sulphuric acid have undergone remarkable altera- 

 tions : the indigo having lost a portion of its hydrogen, and 

 the sulphuric acid a portion of its oxygen, — and these two 

 elements, hydrogen and oxygen, having united to form 

 water. But in the case of the red sulphate, the indigo and 

 the sulphuric acid have entered into combination without 

 undergoing any change. 



As in the composition of the red sulphate the colouring 

 matter is "or appears" unaltered, I was induced to entertain 

 the supposition that it might be beneficially used in dyeing, 

 for obtaining solid blues directly, an operation which might 

 probably replace with advantage the process of obtaining 

 blues from vats. 



