CRYSTALLIZATION EXPERIMENTS 
275 
and cover during the heating. As soon as a well defined 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.‘ 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: Senarmont: 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 recentes sur les facies des cristaux. Paris, 1911. 
