1376 Journal of Applied Microscopy 



ally best to avoid testing it directly for glucinum, but to first practice a separation 

 where the former are removed from the latter. 



Exercises for P7-acticc. 



To a drop of a solution of a pure salt of Gl add KoC^O^ in the manner 

 directed above. Try the experiment several times, varying the amount of the 

 reagent. 



Try again under as nearly like conditions as possible, but this time having 

 first introduced a little HgClg. 



Try the action of HKCjO^ ; (NH4)2C204 ; NaoCgO^. 



Try reagent on salts of Mg; Zn ; Cd ; Cu; Co; Ni. 



Then try mixtures, as for example, Gl and NH^ ; Gl and Mg ; Gl and Al ; 

 Gl and Fe ; Gl and Zn ; Gl and Ca, etc., and also more complicated mixtures. 



///. With Urhnyl Acetate and Sodium Acetate. 



This reaction of glucinum salts has already been alluded to under Sodium, 

 Method II.* The equation for the reaction is the same as that there indicated, 

 save that glucinum replaces the magnesium. 



To the material to be tested a little sodium acetate is added (unless it is 

 known that sodium is present). The drop is then evaporated to dryness, and 

 the solution of the reagent is drawn across the film of dry residue. Skeleton 

 crystals, long, imperfect prisms, and almost colorless tetrahedra result. 



There is, at times, some difficulty in clearly distinguishing between the triple 

 acetate of glucinum, sodium, and uranyl, the double acetate of sodium and 

 uranyl, and the crystals due to a separation of uranyl acetate. It has been the 

 experience of the writer that students trying the method for the first time are 

 invariably in doubt as to the nature of the crystals obtained. 



The tetrahedra of the triple acetate differ only in size and color from those 

 of the double acetate, the former attaining a greater size than the latter, and 

 being only very faintly yellow instead of exhibiting a distinct yellow tint. 



The amount of sodium present must be small, otherwise only the double 

 acetate will appear. 



Salts of ammonium, potassium, and of the calcium group will generally 

 interfere, if present in excessive quantity. 



Phosphates and other compounds precipitating uranium should be absent. 



Free mineral acids must be removed by evaporation to dryness, as has been 

 suggested. 



It is obvious that this method cannot be employed for the detection of gluci- 

 num save in the absence of magnesium, zinc, cadmium, cobalt, nickel, iron, 

 manganese. 



MAGNESIUM. 



The micro-chemical detection of magnesium in complex mixtures is usually a 

 matter of not a little difficulty, since this element is commonly associated with 

 others closely related, which are prone to interfere with or prevent the formation 

 of typical crystals with the reagents employed for its recognition. 



* Jour. App. Micros. Ill, 1900, 985. 



