CRITICAL EXPERIMENTS FOR DETERMINATION OF POTASSIUM, ETC. 611 



Further Trials. 



These were carried out with solutions representing 95 per cent., 82 per cent., 

 33*3 per cent, salts, which were prepared from the same materials as those 

 used for the corresponding trials with Finkener's method. In the case of 

 each kind of salt, indeed, the two methods were worked side by side of each 

 other, so as to give no advantage to either. 



General Method. — A solution representing 0*648 grm. of a " 95 per cent." 

 salt mixed with a few drops of hydrochloric acid, and 32*4 c.c. of 5 per cent, 

 chloride of platinum ; mixture evaporated to a magma, mixed with 2 to 3 c.c. 

 of water, and evaporated again. After cooling, 3 25 c.c. of platinum solution 

 added, and allowed to stand for an hour. So far, all the four analyses 

 conducted in the same way. 



In (1) and (2). — Washing with chloroplatinic acid continued until the 

 impurities by calculation were reduced to about 006 mg. and the S0 3 to 0*012 

 (but a direct test with BaCl 2 showed that there must have been more). The 

 washing then completed with 95 per cent, alcohol. 



In (3). — After decanting off the mother-liquor, the precipitate was washed 

 once, with 1 c.c. of platinum solution. The precipitate was then dissolved 

 in hot water, and the solution, after addition of 2 c.c. of platinum solution, 

 re-evaporated as far as possible on a water-bath. 2 c.c. of water were then 

 added, and the whole allowed to stand for an hour. The precipitate was then 

 filtered off, washed with two successive cubic centimetres of platinum solution 

 (when as a matter of calculation, the impurities should have been reduced 

 to 0*25 mg. ; the S0 3 to 0*06 mg., yet a drop tested with BaCl 2 gave a 

 precipitate), and lastly with 95 per cent, alcohol. 



In (4), Tatlock's directions were strictly obeyed. 



Chloroplatinates dried at 100° to 105°, weighed, and reduced with hydrogen, 

 (wet way), to determine their platinum. 



The results are stated in the following table (in grammes) : — 





Experiment, 



1. 



2. 



3. 



4. 



I. 



Chloride of potassium taken, . 



•61075 



•61033 



•60992 



•60917 



II. 



Chloroplatinate obtained, 



1-9721 



1-9696 



1-9755 



1-9860 



III. 



Platinum from " II", . 



•7927 



•7918 



•7947 



•7964 



IV. 



II. x 0-30435, . 



•60021 



•59945 



•60124 



•60444 





Error = IV. minus I. ; mgs., . 



- 10-54 



-10-88 



-8-68 



-4-73 



V. 



III. X 076117, . . . 



•60338 



•60269 



•60490 



•60620 





Error = V. minus I.; mgs., 



-7-37 



-7-64 



-5-02 



-2-97 



Filtrates — from (1), (2), and (3),* freed from alcohol by distillation : their 

 potassium recovered by Finkener's (sal-ammoniac) process, and determined 



* Those of (4) were lost by a disaster in the laboratory. 



