CRITICAL EXPERIMENTS FOR DETERMINATION OF POTASSIUM, ETC. 597 



extracted was determined, and found to amount to 0*8 mg. The recrystallised* 

 sulphate, when heated in hydrogen gas under a funnel, and (the product) treated 

 with water, left 1'2 mgs. of platinum, corresponding to 0*91 mg. of chloride of 

 potassium. The 004 mg. (which had been present in the sulphate used) are 

 not deducted. 



Experiment II. — A repetition of I., except that 100 mgs. of H 2 S0 4 in the 

 form of standard acid, were added in the recrystallisation, with the view of 

 decomposing the chloroplatinate of sodium suspected to be present. Platinum 

 obtained from the recrystallised salt, = 0*5 mg. = 34 mg. of chloride of 

 potassium (corrected for the potassium in the sulphate of soda used). 



Experiment III. — Three grammes of sulphate of soda used, and the sulphate 

 obtained recrystallised twice, ivithout addition of sulphuric acid. Residual 

 platinum, = 0*4 mg. = 0'30 mg. of chloride of potassium, or 022 mg. after 

 deducting the 0*08 mg. really present. 



Experiment IV. — A repetition of Experiment III., except that 200 mgs. of 

 H 2 S0 4 were added in each recrystallisation. Residual platinum exactly the 

 same; i.e., a quantity indicating 022 mg. of adventitious chloride of potassium. 



Experiments III. and IV. were made side by side of each other. 



Experiment V. — To study the effect of the added sulphuric acid on chloro- 

 platinate of potassium, 0*2006 grm. of pure chloroplatinate of potassium was 

 dissolved in 40 c.c. of boiling water, containing 25 mgs. of H. 2 S0 4 , the mixture 

 evaporated to a magma, and Finkenerised. The resulting salt was " recrystal- 

 lised " again with 25 mgs. of H 2 S0 4 . Both mother-liquors were yellow. They 

 contained, that from the first precipitation 9 mg., that from the second 0*6 mg. 

 of platinum, equal to 0'68 and 0*46 mg. of chloride of potassium respectively. 



Seeing that sulphuric acid, under the circumstances, decomposes chloro- 

 platinate of potassium appreciably, we tried, in 



Experiment VI., the effect of sulphate of lithium on chloroplatinate of 

 potassium, because, supposing it to prove inert towards chloroplatinate of 

 potassium, it would have afforded an admirable reagent for the elimination of 

 foreign chloroplatinates from a Finkener residue. 05 grm. of chloroplatinate 

 of potassium when Finkenerised with addition of 01 grm. of pure sulphate of 

 lithia, yielded a filtrate containing 3 '8 mgs. of platinum, = 29 mgs. of chloride 

 of potassium. On " recrystallising " with 50 mgs. of the lithia salt, the liquor 

 contained 4"0 mgs. of platinum, equal to 3*0 mgs. of chloride of potassium. 



This shows that sulphate of lithia is not available for the purpose aimed at. 



Experiments with Sulphate of Soda, containing added Potassium. 



I. A quantity of sulphate of soda equivalent to 8*73 grms. of chloride 

 (NaCl), and a known weight of a standard solution of chloride of potassium 



* We adopted this word for designating the operation described. 



