CRITICAL EXPERIMENTS FOR DETERMINATION OF POTASSIUM, ETC. 619 



of a salt, which, apart from that trace of sulphuric acid, seemed to be very pure. 

 In its aqueous solution, sulphuretted hydrogen produced no change ; sul- 

 phide of ammonium had no immediate effect, and, on long standing, only an 

 almost invisible precipitate settled out. 0*5 grm. of the salt, when dissolved 

 and mixed with iodide of potassium, gave no precipitate (absence of thallium) . 

 The spectrum-apparatus revealed no trace of potassium. 



In order to, at the same time, determine the sulphuric acid, and rehearse 

 a method for its removal, 5 grms. of the salt were dissolved, chloride of barium 

 added, the precipitate allowed to settle, and weighed. It amounted to 6*5 

 mgs., indicating 045 per cent, of S0 3 in the preparation. 



From the (concentrated) nitrate, the rubidium was precipitated by addition 

 of a slight excess of chloroplatinic acid, the chloroplatinate allowed to settle, 

 and washed by decanting nitration, first with water, then with 50 per cent., 

 and lastly with absolute, alcohol. The weight of the chloroplatinate, after a 

 preliminary drying at 120°, amounted to 1 11 87 grms. 



10094 grms. of this chloroplatinate were dissolved in hot water, in an 

 Erlenmeyer flask, the platinum was reduced out by hydrogen, and filtered off, 

 and the filtrate evaporated to dryness over a water-bath. The residue was 

 dissolved in 50 c.c. of water, and separate portions examined. 10 c.c. when 

 mixed with sulphide of ammonium, gave a mere trace of (FeS and A1 2 3 ?) ; 

 10 c.c. when Nesslerised, gave 0*08 mg. of NH 3 , corresponding to 04 mg. per 

 1 grm. of salt ; 10 c.c. when mixed with chloride of barium, and other 10 c.c. 

 when mixed with sulphuric acid, gave both slight clouds of sulphate of baryta. 

 From the last two tests, it was clear that the application of chloride of barium 

 to our stock of salt would have done little good, and we accordingly decided 

 upon using the preparation as it was. 



A portion of it was dehydrated in a platinum crucible without fusion, 

 then fused very cautiously, and poured out into a platinum basin. 181321 

 grms. of such salt were dissolved in water to 300 c.c, and thus converted into 

 313*522 grms. of a standard solution, of which every 1 grm. contained 57*834 

 mgs. of salt. Three titrimetric determinations of the chlorine gave the follow- 

 ing results : — 



Analysis, 

 Approximate weight of solution taken, 

 Chlorine per gramme of solution, . 



Mean = 16*8226, corresponding to 29*087 per cent, of chlorine in the 

 original salt. 



Taking Rb = 85*4, and Cs = 133*0, the precentages of chlorine in the 

 chlorides of the two metals are — 



In KbCl. CsCl. 



Equal to, 29*337 21047 



1. 



2. 



3. 



10-4 



20*8 



20-8 grms. 



16-8253 



16-8200 



16-8226 mgs 



