CRITICAL EXPERIMENTS FOR DETERMINATION OF POTASSIUM, ETC. 589 



2. Chloroplatinate prepared by precipitating Chloroplatinie Acid with a large excess of 



Chloride of Potassium. 



Experiment. P. Volume of mixture of Reagents p 



r per 1 grm. of KC1 used. 



, 194-65 (196-78 per 

 VII. 40 537 c.c* «! 4C1 parts of loose 



(See context.) ( chlorine). 



3. Chloroplatinate made by precipitating Chloride of Potassium with a large excess of 



Chloroplatinie Acid. 



Experiment. P. Volume of mixture of Reagents pt 



r per 1 grm. of KC1 used. 



VIII. 294 160 c.c. 195-87 



4. Chloroplatinates made from Chloride of Potassium, by evaporating with a large excess of 



Chloroplatinie Acid, washing with first 5 per cent. Platinum Solution, and lastly with 



Alcohol. 



Experiments. P. Volume of mixture of Reagents pt 



r per 1 grm. ot KC1 used. 



IX. 294 (Evaporation), 195-59 \ M 



X.(r.) 294 „ 19601 I *** 



X. (II.) 294 „ 19582 J 1B5 S1 



5. Recrystallised Chloroplatinates. 



Supplementary Experiment to V., 195-54 ^ 



toVa., 195-48 / Mean = 



Experiment XL, (Recrystallisation of X. from water), . . . 195-60 C 195-50 



„ XIL, (Recrystallisation from dilute hydrochloric acid), . 19537 ' 



From our recrystallisation experiments (if our theory be correct), it 

 follows that the true atomic weight of platinum (apart from observational 

 errors) lies at, or is less than, 195 50. 



This number, 195 50, then, affords an upper limit to the unknown number 

 Pt. Seubert's experiments enable us to find a lower limit. 



Seubert, in his Memoir, gives the results of two analyses of one, and 

 of six of another, preparation of chloroplatinate of potassium. The chloride of 

 potassium and the platinum were determined in each case, the loose chlorine 

 only three times. His mean results, referred to 100 parts of substance 

 analysed, were as follows .-—(Mean relative uncertainty means the mean 

 deviation from the mean, measured by the mean itself ; or the uncertainty per 

 unit of the quantity determined). 





Per cents. 



Mean relative uncertainty. 



Platinum, . 



40110 



± 0-0004 



Chloride of potassium, . 



30-685 



± 00010 



Loose chlorine, 



29-144 



± 0-0017 



Error, water, &c, . 



0061 





100-000 

 * Per 1 grm. chloride of potassium as calculated from the platinum, assuming Pt to correspond to 2KC1. 



