Annual Report of the Council. 297 



elaborate experiments Dale found that by working under 

 strictly the same conditions, the loss is quite constant, and 

 thus he discovered a method by which the value of indigo 

 can be quickly and exactly determined. This method was 

 communicated to the writer by Mr. Dale and published in 

 the second edition of Muspratt's dictionary. 



Ullgren later came to the similar conclusions as Dale 

 and published a paper on the subject in Liebig's Annalen. 



Other analytical processes were devised by Dale, as that 

 for estimating tin by potassium dichromate, and his fertile 

 and resourceful mind led him to many other improvements 

 in technical and analytical chemistry. In the year 1858 

 Perkin discovered aniline-purple, or mauve, the first 

 aniline colour which appeared in the market. He obtained 

 it by the action of potassium dichromate on sulphate of 

 anilin. Dale, in conjunction with Caro, endeavoured to 

 find an equally effective oxidising agent, and both having 

 a practical acquaintance with calico-printing, hit upon one 

 which a purely scientific chemist would probably not have 

 thought of. They employed a mixture of copper sulphate 

 and common salt. By using this, however, acid was 

 liberated which interfered with the production of the colour- 

 ing matters, and the further improvement of the process 

 which Dale devised was a judicious addition of an alkali. 

 At the same time a useful black pigment was produced, 

 which is the more interesting as it may be said to have led 

 to the discovery of aniline-black by Lightfoot, to whom the 

 reaction was known. 



Among the artificial colouring matters which to-day are 

 largely manufactured, the class of the azo-colours is one of 

 the most important. Of these in 1863 only aniline-yellow 

 was known. Dale, in conjunction with Caro and Martius, 

 soon brought two new ones, known as Manchester Yellow, 

 or Martius Yellow, and Manchester Brown, or Bismark 

 Brown, which are still specialities of Messrs. Roberts, Dale 



