CRITICAL EXPERIMENTS FOR DETERMINATION OE POTASSIUM, ETC. 575 



Adopting the mean, it would follow that Pt = 194*65, and that this Pt is 

 combined with 211192 = 595663 x CI, supplemented by 004337 x (OH or $0). 

 But we have no excuse for presuming that oxychloride-oxygen is present ; on 

 the other hand, we have good reason for suspecting the presence of surplus 

 chloride of potassium. Referring the mean results to 4 x CI parts of loose 

 chlorine, we have 



Platinum, . 19678 



1-01097 xK,Cl 8 150-82 



4 x CI of loose CI, 141-82 



Total, 489-42 



AndM, = 493-67 



Water (?) 425 



This, we believe, is the correct mode of interpreting the analysis. 

 It does not follow that 19678 is the true atomic weight of platinum. 



Experiment VIII. (Matthey's Metal). 



All the experiments reported on so far were made with platinum solu- 

 tions, made by means of the ordinary aqua regia process. We have reason to 

 suspect that these solutions contained small quantities of the nitroso-com- 

 pound PtCl 6 (NO) 2 , which may have had an evil effect, although it is not quite 

 easy to see how this can have been the case. However this may be, the 

 following experiments (VIII. and IX.) are free of this flaw, because they were 

 carried out with platinum solution made by the chlorine process (see 

 page 565). Their most important feature, however, is that a very con- 

 siderable excess of chloroplatinic acid was used in the preparation of the 

 chloroplatinates. 



In Experiment VIII. 3'045 grms. of chloride of potassium were dissolved 

 in 40 c.c. of water, and precipitated with 120 c.c. of a platinum solution 

 containing 6*0 grms. of platinum, so that the platinum added per 2KC1 parts 

 amounted to 294-0 parts. The potassium salt was poured into the platinum 

 solution, the mixture allowed to stand over night, the precipitate washed by 

 decanting filtration, first with 5 c.c. of water {i.e., chloroplatinic acid solution), 

 and then with absolute alcohol; the aqueous and alcoholic washings were 

 preserved separately. The precipitate was dried at 100° to 105° in a watch- 

 glass for 4£ hours, and then for another hour in a Geissler tube at the same 

 temperature. The precipitate acquired a constant weight in a remarkably 

 short time. After having been dried, it was divided into three parts, 

 A, B, C. 



A = 3-3511 grms. was devoted to a direct determination of the water. 

 Water obtained = 30-8 mgs. = 091 9 per cent. 



