ESSAY XXII. 



EXPERIMENTS ON THE COLOURING MATTER IN BERLIN 

 OR PRUSSIAN BLUE. 1782. 



TOWARDS the beginning of the present century, Mr. Diesbach, 

 a manufacturer of colours at Berlin, with the assistance of 

 Dr. Dippel, accidentally discovered the blue colour since 

 called Berlin or Prussian blue. They kept this preparation 

 with great secrecy, till Woodward published the whole 

 process in 1724. After this period, several chemists have 

 endeavoured as well to improve the colour as to give an 

 explanation of its origin. Brown, both the Geoffreys, and 

 the Abbe Maynan. are known on account of their papers 

 written upon this subject ; but it was reserved for Macquer, 

 who published a dissertation upon it in 1752, to represent 

 the whole in a connected view. After him several have 

 attempted to determine the nature of the matter which in 

 general unites with the metallic calxes, when they are 

 precipitated from their solutions by the lixivium sanguinis, 

 and which in the preparation of the Prussian blue gives to 

 the iron a blue colour ; but they have advanced no further. 

 Some are of opinion that it is phlogiston which comes into 

 action here, and thence the name phlocjisticated alkali. Others 

 think that it is an animal acid. The cause of this uncertainty 

 is, that there has been hitherto no method discovered to obtain 

 this colouring matter in a perfectly pure state, it being 

 hitherto always united with some heterogeneous substance. 



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