CRITICAL EXPERIMENTS FOR DETERMINATION OF POTASSIUM, ETC. 601 



B. KC1 obtained from first ether-alcohol filtrates of Experiment II., . . 73 

 B'. KC1 obtained from second ether-alcohol 61trates of Experiment II., . . - 58 



C. KCl from the two sal-ammoniac liquors, worked conjointly : — 



Calculated from PtCl 6 K 2 , . 4 - 81 •} mean = 5"03, deducting 0'23 present in 



„ Pt, . . 5"21 j sal-ammoniac, ..... 4 - 80 

 X. Ether-alcohol filtrates of Experiment IJa. were not worked up ; they con- 

 tained, let us say, the mean of B and B', = 065 



Total chloride of potassium found = A +B-f-B'+C+X, . = 2503 



Excess of KCl found, = 0'88 



The relative exactitude in Experiments II. and Ha., it is true, is not very 

 high; but the absolute precision of the results is high, considering that the 

 substance analysed was, virtually, a mixture of the two chlorides, NaCl and 

 KCl, which contained only 0*2766 per cent, of the latter. Hence the Finkener 

 process, whatever it might be otherwise, is invaluable as a means for the 

 determination of small quantities of potassium which escaped the meshes of 

 other analytical methods, and in this sense, amongst others, we have used it 

 largely. 



Experiments on synthetically prepared Mixtures containing relatively 

 large quantities of Potassium. 



We could not detail all our experiments of this kind without filling a 

 great many pages. We prefer to give the conclusions which we drew from a 

 considerable experience concerning the Finkener process, and then pass on to 

 reporting, mainly, on our final series, which was carried out by what we at the 

 end came to recognise as the best form of the process for general purposes. 

 The conclusions referred to are these, — 



1. In the analysis of a mixture of chlorides and sulphates of the bases 

 K 2 0, Na 2 0, MgO for K 2 0, it is not necessary to begin by converting the 

 bases into normal sulphates ; # it suffices to add a sufficient quantity of 

 sulphuric acid, equivalent, by calculation, to the chlorine present. In the 

 test analyses to be reported on, we added measured volumes of standard 

 sulphuric acid calculated from our knowledge of the weight of chlorine 

 present. In actual practice, a preliminary determination of the latter by, say, 

 Mohr's method, would give the necessary guidance. 



2. In the treatment of the residue (of chloroplatinate of potassium plus sul- 

 phates) it is expedient to add, first a sufficiency of absolute alcohol, say 10 c.c, 

 to allow to stand for some time, and then to add the necessary (5 c.c. of) ether, 

 and allow to stand longer, but under a small bell-jar on a glass plate. For 

 a long time it was our rule to let the alcohol act for half an hour, and the 

 alcohol and ether for other two hours ; but we subsequently found that five 



* Finkener does not say it is ; but for a time it was our method. 

 VOL, XXXIII. PART II. 4 T 



