BOTANICAL MICROTECHNIQUE. 



9. Potassium, K. 



82. Since ammonium cannot occur in the ash, platinum 

 chloride may well serve for the recognition of potassium. 

 The potassium-platinum chloride thus formed crystallizes in 

 regular octahedra and cubes. According to Schimper (II, 

 .213) the ash is dissolved in a drop of acidified water, is 

 warmed until dry, and the reagent is added before or after 

 cooling. But the reagent used must first be tested with 

 much care to show that it is really free from potassium. 

 This may be done by letting a drop of the reagent slowly 

 evaporate on the slide. 



10. Sodium, Na. 



83. The ur any l-magne slum acetate recommended by 

 'Streng (I) serves excellently for the recognition of very 

 small quantities of sodium. It forms with sodium a double 

 salt of the composition CH s CO a Na + (CH 8 CO,) 2 UO,+ 

 <CH 9 COO) a Mg + (CH 9 COO),UO + 9H 3 O. This compound, 

 very poor in sodium and therefore formed in the presence 

 of very small quantities of sodium, forms small colorless or 

 very pale yellowish rhombohedral crystals, which are little 

 soluble in water and almost insoluble in alcohol. 



Since the solution of the uranium salt extracts sodium 

 from glass vessels on long standing, Streng (III) recom- 

 mends the direct addition of the solid magnesium-uranyl 

 .salt. 



Schimper (II, 215) used uranyl acetate for the recogni- 

 tion of sodium, as it causes the formation, on evaporating, 

 of sharply developed tetrahedra of sodium-uranyl acetate 

 <CH 3 COONa+(CH 3 COO) 2 UO), of which the larger ones 

 appear faintly yellowish. In the presence of very small 

 quantities of sodium simultaneously with magnesium there 

 is formed, of course, the above mentioned uranyl-magnesium- 

 ;sodium acetate. 



