and Laboratory Methods. 1125 



tinct green, then add a tiny drop of hydrochloric acid, thus converting the 

 manganate into permanganate. The reagent is then allowed to flow in. The 

 crystals of potassium perchlorate which separate have the same form as before, 

 but are a beautiful deep rose color, the intensity varying with the amount of per- 

 manganate present. In a few moments the liquid is completely decolorized, and 

 the precipitated crystals deeply colored. Performed in this way the test is an 

 elegant and very striking one. 



Exercises for Practice. 



Try reaction with different salts of potassium. 



Introduce sodium permanganate into the test drop, and test as above. 



Try the reaction on the other members of Group I, 



Make a mixture of K and Na salts. Treat a drop of a solution of this 

 material with perchloric acid, evaporate, treat with the reagent again, and again 

 evaporate, extract the dry residue with alcohol, and test the alcoholic extract for 

 sodium. 



Try the action of perchloric acid on members of the magnesium group, and 

 the calcium group. 



XL AmmoiiiuDi Fluosilicate. 



As performed in the ordinary manner, with solutions of moderate concentra- 

 tion, no separation of crystals results. It is only under unusual conditions, or by 

 evaporation, that potassium fluosilicate can be made to appear. From a practical 

 standpoint, therefore, this reagent is without value for the detection of potassium. 

 The salt KgSiFg crystallizes as cubes, octahedra, and combinations of these 

 forms. 



XII. CofiTcrsion into Sulphate^ Double Sulphates, etc. 



The remarks made under Sodium, with reference to a similar method, apply 

 with equal force to potassium. This method requires too much care and great 

 experience, and is therefore impracticable save for the expert crystallographer. 



RUBIDIUM AND CESIUM. 



It is seldom, indeed, that the chemist is called upon to make tests upon a 

 substance containing rubidium or cesium. For this reason, and also because the 

 present series of articles purports to give merely an introduction to the methods 

 of micro-chemical analysis, these elements can be discussed together and dis- 

 missed with but few words. 



Among the reagents which can be employed for the detection of these two 

 elements, three can be selected as being the most satisfactory. 

 I. Potassium Chlorplatinate. 

 II. Ammonium Silicomolybdate. 

 III. Stannic Chloride. 

 Of these, I and II serve for the detection of both rubidium and cesium, and 

 III for cesium alone. 



