1374 



Journal of Applied Microscopy 



Remarks. — If it is desired to hasten the separation of the glucinum salt, tip 

 ^ , ^ ., ^ up the slide and add a drop of alcohol to the test drop 



>4^/iv^~^ ^^ter the reagent has been drawn across. Generally 



^r ^f r^\ ^^ the addition of the alcohol is essential in order that 



any crystals of the glucinum chlorplatinate be obtained. 



"^^A^^^ rl^-A^ \1 ^ ^^^ ^^^^ ^^ satisfactory only when the air of the 

 - ' ^^ laboratory is quite dry. In a moist atmosphere the 



glucinum chlorplatinate is deliquescent, hence the test 

 fails. In such an event it is necessary to add abso- 

 lute alcohol, or place the preparation in a desiccator, 

 or cover it with a watch-glass carrying a drop of con- 

 centrated sulphuric acid. 



In case the quantity of glucinum present is small, 

 and that of the members of Group I great, it is essential that sufficient reagent 

 be added to unite with all. If, therefore, on examination of the preparation 

 after the addition of the chlorplatinic acid, it is seen that members of the 

 potassium group are present, it is wise to make a second addition of the reagent, 

 and follow it with alcohol. 



When sodium is present in considerable amount, it is often difficult to dis- 

 tinguish the glucinum salt from the sodium chlorplatinate ; if, however, the 

 preparation be examined between crossed nicols, the problem is simplified, since 

 the chlorplatinate of sodium exhibits oblique extinction (triclinic) and a brilliant 

 play of colors, while the glucinum compound gives parallel extinction (tetragonal) 

 and but faint colors (usually none). The chlorplatinates of the potassium group 

 are isometric. 



If solutions containing glucinum in the form of sulphate are employed, care 

 must be taken to avoid confusing this salt with the chlorplatinate, since the 

 glucinum sulphate, GISO4 • 4H2O, which is also to be referred to the tetragonal 

 system, sometimes separates in thin, six-sided plates. 



//. Normal Potassium Oxalate added to solutions of salts of Glucinum causes 

 the separation of a difficultly soluble Double Oxalate of Potassium and Glucinum. 

 2 K2C2O4 + GISO4 = K2C2O4 . GIC2O4 + K2S04- 



Method. — To the moderately concentrated solu- 

 tion add a little acetic acid, then a fragment of the 

 reagent about twice as large as is usually the case 

 in micro-chemical work. Almost immediately large, 

 clear, colorless, highly refractive prisms of the 

 monoclinic systems are obtained. These prisms 

 unite to form twins and radiating masses (Fig. (»5). 



Remarks. — The appearance of the crystals 

 varies greatly, according to the amount of the 

 reagent present, as compared with that of glucinum. 

 Too little potassium oxalate will yield only a pre- 

 cipitate of tiny crystals which probably consist of ^'^ 

 the normal oxalate of glucinum. Too much re- 



■=» Fig. 65. 



