SCIENCE IN THE INDUSTRIAL WORLD 



in any desired quantities. Other color-makers took up 

 the problem at once and soon solved it by various meth- 

 ods, so that this color took its place beside ultramarine 

 as a regular commercial product. 



Very fine grades of Prussian blue are frequently 

 designated as "Chinese blue," and may be made in the 

 following manner: 



One hundred parts of sulphate of iron are dissolved 

 in cold water and ten parts of sulphuric acid auJed to 

 the solution. This solution is then mixed with a 

 solution of one hundred parts of yellow prussiate of 

 potash. As a result, a bluish- white precipitate is formed, 

 which settles to the bottom of the vat. To this precipi- 

 tate a mixture of about twenty parts of bleaching- 

 powder and water is added, and thoroughly stirred, 

 after which a little hydrochloric acid is poured in, on 

 the addition of which the characteristic blue color 

 gradually develops. This blue pigment settles to the 

 bottom in a thick mass from which the overlying liquid 

 is run off. It is then washed, drained, and finally 

 pressed into pans and dried in dark ovens at a tempera- 

 ture not higher than 130 F. This is, of course, only 

 one of the many methods of manufacture, but it may be 

 taken as a characteristic one. 



The Prussian blues have a characteristic greenish- 

 blue tint not seen in any other pigment. They are 

 permanent as oil-colors, and their coloring power is 

 remarkable, one part of Prussian blue giving a dis- 

 tinctly blue color to six hundred parts of white lead. 

 When used as a water-color Prussian blue has the pe- 

 culiarity of fading considerably when exposed to light 



[3] 



