CRITICAL EXPERIMENTS FOR DETERMINATION OF POTASSIUM, ETC. 609 



solvent, the flasks stopped up, and allowed to stand with occasional agitation. 

 Whenever the precipitate threatened to dissolve completely, an additional 

 weighed instalment of chloroplatinate was added. After six days the contents 

 of the flasks were weighed, filtered, and the filtrates analysed for the dissolved 

 chloroplatinate. The temperature during those six days varied from about 

 13° in the mornings, to about 16° 5 in the evenings. The results were as 

 follows : — 



100 parts by weight of solvent dissolve q parts of PtCl 6 K 2 . 



Solvent. q. 



A. Water, 0628 



B. Hydrochloric acid of 5 per cent., ....... 0662 



C. " 5 per cent." chloride of platinum solution, 0233 



D. Solution of chloride of platinum, containing 0"05 grm. of added (real) 



HC1, and 0'05 grm. of platinum, per c.c, 0168 



E. Sulphuric acid, containing |S0 3 = 40 grms. per litre, . . . . - 900 



Methods of Analysis : A. and B. — Evaporation to dryness, and weighing of 

 residue, dried at 150° C, as PtCl 6 K 2 . 



C. and D. — Evaporation to dryness on a water-bath, treatment with abso- 

 lute alcohol, and weighing of the washed precipitate after drying at 150° as 

 PtCl 6 K 2 . 



E. — The liquid almost neutralised with pure (potassium-free) caustic soda, 

 the platinum reduced out by hydrogen, and weighed. 



We regret now not to have determined the action of stronger solutions of 

 chloroplatinic acid, because Mr Tatlock virtually begins by washing his 

 chloroplatinate with a " 17 per cent." solution of the reagent. 



In now passing to our analyses, we begin with a series in which we 

 deliberately departed from certain of Mr Tatlock's rules, in order to bring 

 the errors into greater prominence, and also on the chance of being able 

 to rectify these by suitable modifications of the process. Let us at once 

 confess that our success in the latter direction amounted to very little, if 

 anything. 



Preliminary Trials. 



Experiment I. — The solution analysed contained exactly 3471 grm. of 

 chloride of potassium, and about 100 mgs. Na 2 S0 4 , and 150 mgs. of MgS0 4 ; 

 it consequently represented a salt of "58 per cent." Evaporated clown with 

 platinum solution equal to 515 mgs. of platinum, or 50 mgs. more than 

 demanded by the potassium. Residual magma washed five times, each time 

 with 5 c.c. of water, then exhaustively with absolute alcohol. The chloro- 

 platinate dried at 150°, and weighed ; then dissolved in water, the platinum 

 reduced out, and weighed likewise. 



VOL. XXXIII. PART II. 4 U 



