CRYSTALLIZATION EXPERIMENTS 275 



and cover during the heating. As soon as a well denned sublimate is obtained 

 upon the slide allow the preparation to cool: transfer the slide film side up to the 

 stage of the microscope and study the crystals which have been formed. 



19. Sublime Arsenic trioxide'in the manner described above in 18. Be sure to 

 have the slide cool. Repeat the experiment but, this time heat the slide before 

 laying it upon the watch glass, thus having a warm surface upon which the crystals 

 will be formed. Compare the sublimates which have been obtained. 



Colored Crystals from Colorless Compounds. 



20. A number of colorless inorganic salts, when crystallized from solutions con- 

 taining certain dyes, yield beautifully colored crystals. 1 Make a pencil mark 

 upon a piece of white paper; lay an object slide on the paper over the mark; now 

 place a drop of a concentrated solution of Methylene Blue on the slide in such a 

 position as to be over the mark, and add very carefully water until the black mark 

 can just begin to be seen when viewed through the blue solution. Dissolve a little 

 Lead nitrate in the blue solution and induce crystallization; there will be obtained 

 octahedra of Lead nitrate colored deep blue by the Methylene Blue. 



1 See: S6narmont: Ann. chim. phys. (3) 41 (1854) 326. Pogg. An. 91 (1854) 491. 

 Becquerel: Ann. chim. phys. (6) 14 (1888) 170. Carmichel: Ann. chem. phys. (7) 

 6 (1895) 433. Gaubert: Recherches rScentes sur les facies des cristaux. Paris, 191 1. 



