CRITICAL EXPERIMENTS FOR DETERMINATION OF POTASSIUM, ETC. 591 



3. By determining the same ratio in a salt prepared from salt of Darstellung II. 



by recrystallisation, 19516 



4. By determining the same ratio in a salt prepared from chloroplatinic acid by 



addition of about 2 - 5 times the calculated weight of sal-ammoniac, washing, 



and recrystallising the precipitate (Darstellung IV.), ..... 195-50 



5. By determining the weight-ratio of platinum to total chlorine in three pre- 



parations, namely : — 



(a) One of Darstellung II not recrystallised. 



(b) One of Darstellung III (precipitation of chloroplatinic acid, 



prepared by means of chlorine gas and hydrochloric acid, with 

 a somewhat considerable excess of sal-ammoniac). 



(c) One of Darstellung IV. 



The values Pt (calculated by us from his numbers for platinum and total 

 chlorine) were as follows : — 



Salt, a, b, c, 



Pt, . = 195-55 19578 19610 



Now, all these chloroplatinates were liable to contain water. Those 

 which were not recrystallised, — excepting (1), — were almost bound to contain 

 free sal-ammoniac ; those which were, probably contained OH instead of part 

 of their CI. In the case of determinations (5), (a), (b), (c), however, the presence 

 of water does not tell upon the results ; hence, if we had only these three 

 analyses to go by, we should say, results (a) and (b) are probably too low, be- 

 cause (free sal-ammoniac) chlorine was determined as chloroplatinate-chlorine ; 

 (c) is probably too high, because the salt contained oxygen in place of part of 

 its chlorine, and we should take the mean of the mean of (a) and (b), and of 

 (c) as the most probable value, and put clown Pt = 195*89 ± 22. 



Of result (1) it is difficult to say whether it is more likely to be too high or 

 too low, because it may have contained surplus platinum ; we must accept the 

 195 '18 as it stands. 



Result (2) is sure to be too low, because it must be presumed to have 

 contained both water and surplus sal-ammoniac. Hence the value 194 53 

 is less than the true Pt. 



Preparations (3) and (4) were probably free of surplus sal-ammoniac or 

 platinum; but they may have contained water, which would make the re- 

 sulting Pt too low ; and they probably contained hydroxyl in place of their 

 chlorine, which would tend the opposite way. But result (3) is derived 

 from only one analysis. Hence (as (2) is out of court), the most reasonable 

 mode of utilising the determinations (1) to (4), is to take the mean of (1) and 

 (4) ; or rather, as (1) included six and (4) included nine analyses, to take 

 Pt= (6x195-18 + 9x195-50) -s- 15 = 195-37, and assuming this to have, say, 

 10 times the " weight" of the result deduced from analyses (5), we have, finally, 

 Pt = 195-42, which number falls in well enough with Seubert's analyses of 



