1 882.] Microscopy. 617 



at o° are almost colorless, becoming at 70 light blue with green 

 stripes, and at 90 show brilliant colors. 



The four per cent, solution of manganese sulphate shows broad 

 scales, silver white to gray in color, and which are partly serrated 

 at o°, as well as at 6o° and 90 . If the sample is left by itself 

 for several days, polarizing spheres will appear; these are so 

 peculiar that the manganese can readily be recognized from them, 

 especially as no other metal forms such spheres. 



Cadmium presents the most characteristic formations of all the 

 metals; a four per cent, solution of the sulphate produces large 

 spheres containing ellipsoids, which radiate from the center and 

 are marked by regular transverse depressions. This formation can 

 be recognized without a Nicol's prism, and therefore it is not the 

 result of the polarized light, but evidently depends upon the 

 mechanical arrangement of the crystals. On using the Nicol the 

 spheres show at o° a beautiful blue or green cross, whose color 

 zones increase with the turning of the prism until 90° is reached, 

 when the most beautiful colors of the rainbow are manifested, 

 while the ellipsoid becomes darker, better defined, and the trans- 

 verse depressions are marked by dark spots. These phenomena 

 become still more characteristic when observed over a plate of 

 mica. From more dilute solutions of the cadmium sulphate, it 

 is possible to obtain the spheres, but the peculiar structure is not 

 observed. 



If a two per cent, solution of iron sulphate be mixed with a 

 one per cent, solution of sodium bicarbonate, the drop soon be- 

 comes cloudy, and is covered with a gold lustrous film of the 

 oxide ; after drying the specimen shows no spheres, but if it is 

 allowed to remain quiet for two days, small crystals of iron car- 

 bonate are formed ; these show the phenomena of polarization 

 distinctly, but in a very peculiar manner. 



Uranium sulphate assumes the most beautiful forms of all the 

 metals ; a four per cent, solution is taken, and at least twelve hours 

 are necessary to produce the desired formation. It can readily 

 be recognized with a pocket lens, and resembles beautifully 

 colored asters or corn-flowers. Less frequently it occurs in the 

 form of envelopes with velvet-blue, narrow, and purple-colored 

 broad triangles, which mav also be recognized without the Nicol, 

 and therefore are not produced by polarized light but result from 

 the mechanical arrangement of the crystals. 



The mercuric sulphate is difficultly soluble, but it can easily be 

 bought into solution by the addition of a few drops of nitric 

 ac "d. It forms figures similar in shape to a Maltese cross, of 

 superimposed scales, which are very unstable. 



Silver may easily be determined, and in such a way that it is 

 n ot easily mistaken for any other metal. A drop of a two per 

 u: 'it. solution of silver sulphate deposits bright points which may 

 " dete cted with the naked eve ; at O these appear as complete 



