CRITICAL EXPERIMENTS EOR DETERMINATION OF POTASSIUM, ETC. 615 



Salt of, 

 A about, 



(2) 



95 per cent. 

 •610 



Analysis, (1) (2) (3) 



Error, --26 --26 +225 



(4) 

 + •28 



(3) 



82 per cent. 

 •520 



(1) (2) (3) (4) 



-•34 +-25 --06 --07 



(4) 



33 - 3 per cent. 

 •215 grm. 



(i) (2) (3) (4) 

 -•19 --01 --41 +-03 mg. 



Mean error, = ± 037, or excluding No (3) under (2), = ± 020 mg. We 

 see that the degree of precision afforded by the two methods is about the same, 

 and is amply sufficient for all practical purposes. But it still remains to be 

 seen how far the Tatlock method is available for the analysis of salts which 

 are relatively poor in potash. 



Analyses made with the view of deciding this question will be submitted 

 presently ; but we prefer to interpolate a duplicate analysis, by both methods, 

 of an imitation of the double salt MgK 2 S 2 8 + 6H 2 0. 



5370 grm. of chloride of potassium was converted into neutral sulphate 

 (obtained 6273 grm. equivalent, by calculation, to 0*5368 of KC1) ; this was 

 dissolved in water, and diluted to a known weight. Two portions of the 

 solution were weighed out, each mixed with the calculated weights of a 

 standard solution of MgS0 4 , prepared from pure oxide by solution in dilute 

 sulphuric acid, and analysed, one by the Tatlock method, the other by our 

 form of the Finkener process. 



Found by the method of 



I. Chloride of potassium used, . 

 II. Chloroplatinate obtained, 



III. II. x -30627 (see page 614) = 



IV. Platinum from II., 

 V. IV. x 0-76084 (see page 614) = 



"Excess" of KC1 found by III., 



v 

 » » * •> 



The Tatlock method, as we see, gave a deficit of about 1 mg. of KC1 ; but 

 this, after all, is only arrrth of the quantity to be determined, which suffices for 

 all purposes ; or, in other words, the Tatlock method works well enough 

 even with unmixed sulphates. 



The substance analysed contained the equivalent of about 50*6 per cent. 

 ofKCl. 



We now pass to 



Finkener. 



Tatlock. 



•29771 



•23929 grm 



a 



•7782 „ 





•23834 „ 



•3913 



•3119 „ 



•29772 



•23731 „ 



... 



- 0-95 mg. 



+ 0-01 



-1-98 „ 



A Set of Three Analyses of a "10 per cent." Salt. 



A standard solution was prepared, which represented a mixture containing 

 (about) 79 of NaCl, 6 of Na 2 S0 4 , and 5 of MgS0 4 in 90 parts. The 10 per 

 cent, of KC1 were weighed out specially for each analysis, as a standard 

 solution. 



Analysis (1) — Solution Finkenerised with twice the calculated weight of 



