460 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The most minute quantities of lithia can be recognized by their 

 ojDtical behaviour. 



Lime may be detected in several different ways ; if a drop of a 

 2 per cent, solution of calcium chloride is mixed with a drop of a 

 1 per cent, sodium bicarbonate solution, the drop will become 

 cloudy ; and after drying it appears white and shows distinct dendritic 

 stars, which consist of an accumulation of small crystals. Barium 

 and strontium salts fail to show this reaction, or only in a very 

 indistinct manner. Lime is best recognized under the Microscope 

 when it is in the form of the sulphate, and is prepared by mixing a 

 drop of the soluble lime salt with a drop of sodium sulphate. The 

 sulphate crystallizes in stellar-shaped crystals, which cannot readily 

 be mistaken for any other forms. 



Barium nitrate assumes mossy, glistening like silver, colourless 

 dendritic forms ; while strontium nitrate takes the form of radiating 

 needles, which are bluish at 0°, and at 90° are blue, green, and red. 



Magnesia may, even when present in the most minute quantities, 

 be detected by the Microscope. The sulphate forms colourless clusters 

 of needles, which do not become coloured even at 90°. 



The wpper sitl/phate takes the form of step-like prisms, which at 

 0° are almost colourless, becoming at 70° light blue with green stripes, 

 and at 90° show brilliant colours. 



The 4 per cent, solution of manganese sulpliate shows broad 

 scales, silver white to grey in colour, and which are partly serrated 

 at 0°, as well as at G0° and 90°. If the sample is left by itself for 

 several days, polarizing sj^heres will appear ; these are so peculiar 

 that the manganese can readily be recognized from them, especially 

 as no other metal forms such sjjheres. 



Cadmium presents the most characteristic formation of all the 

 metals ; a 4 per cent, solution of the sulpliate produces large 

 spheres containing ellipsoids, which radiate from the centre, and are 

 marked by regular transverse depressions. This formation can be 

 recognized without a Nicol 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 0° a beautiful blue or green cross, whose colour-zones increase 

 with the turning of the prism until 90° is reached, when the most 

 beautiful coloiirs of the rainbow are manifested, while the ellipsoid 

 becomes darker, better defined, and the transverse depressions are 

 marked with 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 2 per cent, solution of iron sulphate be mixed with a 

 1 per cent, solution of sodium bicarbonate, the drop soon becomes 

 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 carbonate are formed ; these 

 show the phenomena of polarization distinctly, but in a very peculiar 

 manner. 



