1122 



Journal of Applied Microscopy 



salts, slightly acidified with hydrochloric acid, beautiful, large, colorless, octa- 

 hedral crystals of the compound K2SnClg sometimes separate. Generally the 

 conditions which obtain are such that owing to the solubility of the potassium 

 stannic salt, nothing is seen until the test drop has evaporated almost to dryness, 

 or until alcohol is added. 



There seems to be some doubt as to whether we should call this salt a true 

 chlorstannate or a double salt of the formula "JKCl • SnCl4. If it is true that 

 we have chlorplatinic acid in solutions of platinum chloride, by analogy we can 

 consider that in the case of the potassium-tin compound we have to do with a 

 salt of chlorstannic acid. Moreover, the similarity of the chlorstannates of K, 

 Rb, Cs, and NH^ to the chlorplatinates of these elements is very striking. 



Properly speaking, stannic chloride is not a suitable reagent for potassium, 

 since the salt formed is too soluble. This reagent is, however, one of our most 

 valuable salts for the detection of cesium (q. v.). 



The chlorstannates of ammonium, rubidium and cesium (and thallium) are 

 far more insoluble than the potassium salt. 



VII. With Cerous Sulphate. 



Cerous sulphate added to solutions of salts of potassium acidified with sul- 

 phuric acid, gives rise to the formation of potassium cerous sulphate. 



The reagent is most easily obtained in the form of the eerie oxide, and can 

 be kept for use in this state. It can be brought into the proper condition for 

 use by being treated as follows : Place a small drop of sulphuric acid on platinum 

 foil, add a little of the oxide, and heat until most of the acid has been driven off. 

 Add more acid and heat again. This treatment should produce a product 

 almost completely soluble in water. Add a drop or two of hydrogen peroxide, 

 and warm the preparation; the solution being acid, the HoOo acts as a reducing 

 agent, and a clear, colorless liquid results. Evaporate, and then dissolve in 

 sufficient water to make a dilute solution. 



A drop of a solution of 

 the reagent is allowed to jss 



flow into a drop of that of 

 the substance to be tested. 

 Both drops must be dilute. 

 The preparation is warmed 

 very gently at the zone 

 of union. The salt 

 K2SO4 . Ce^CSOJg . 

 2H2O rapidly separates as 

 very minute, more or less 

 spherical masses. When 

 the solutions are sufficient- 

 ly dilute, or if the preparation is allowed to evaporate spontaneously, tiny but 

 well formed colorless hexagonal plates are obtained (Fig. 34 B). 



Sodium treated in the same way gives, as has already been stated under the 

 head of this element, very small lenticular and fusiform crystals, and dumb-bell- 



Fig. 34. 



