6i6 General Notes. [July, 



the boric acid be moistened with a drop of the two per cent, solu- 

 tion of sodium bicarbonate, the dried drop will be found to consist 

 of beautiful polarizing spheres, which in their center inclose a 

 small white cross ; this on turning the Nicol prism also revolves. 

 Occasionally dendritic stars instead of the spheres are formed. 



The alkalies possess such optic properties that they can be 

 definitely and certainly distinguished by the microscope. In mak- 

 ing those tests it is best to employ the sulphates for the examina- 

 tion, as they are the most constant in their composition, and in 

 the drying the samples will not absorb moisture from the air and 

 so produce forms which may readily be recognized. Four per cent, 

 solutions were made of the alkalies soluble in water. 



The test with potassium sulphate gives, at o° of the Nicol, a 

 series of rhombic plates, which are not very well defined ; at 90 

 blue rims with yellow or red spots are developed; these cannot 

 be taken for any other alkali. 



Sodium sulphate will be recognized just so soon as it becomes 

 dry by its percipitation. In the darker field of the microscope it 

 appears dull, and silvery-white in hopper-shaped quadratic crys- 

 tals. 



The ammonium sulphate assumes such peculiar shapes that it 

 cannot be mistaken for any other salt. At o° the crystals are 

 hardly recognizable ; at 90 they appear like partly decomposed 

 walls built of gray blocks, with blue and brown rims. 



Lithium sulphate forms clusters of prismatic needles which at 

 O show beautiful colors and a blue cross, which at 90 becomes 

 black. _ The most minute quantities of lithia can be recognized 

 by their optical behavior. 



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

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

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

 come 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 micro- 

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

 mixing a drop of a soluble lime salt with a drop of sodium 

 sulphate. The sulphate crystallizes in stellar-shaped crystab, 

 which cannot readily be mistaken for any other forms. 



Barium nitrate assumes mossy, glistening like silver, colorless 

 dendritic forms; while strontium nitrate takes the form of radiat- 

 ing needles, which are bluish at o°, and at 90 are blue, green, 



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

 be detected by the microscope. The sulphate forms colorie 

 clusters of needles, which do not become colored even at 90 • 



The copper sulphate takes the form of step-like prisms, vvn 



