632 PROFESSOR DITTMAR AND MR JOHN M'ARTHUR ON 



Hence, for the composition of the precipitate according to experiments (1) 

 and (2) — 



Platinum, 196*58 



2NH 4 C1, 107-01 



4-01 x CI, 14217 



Total, 445-76 



(C : A ) x 107-012, = 449-68 



Unaccounted for, = 3-92 



Probably part of the 196 58 parts of platinum is combined with the 

 001 x CI and hydroxyl into Pt(Cl or OH) 6 H 2 , which would account for part of 

 the 3 92 of undetermined components. 



These experiments again are compatible with any value for the atomic 

 wefght of platinum, from 196*58 down to about 190. 



Yet our experiments are of some value, because they show that if we weigh 

 sal-ammoniac as chloroplatinate of ammonium, or as " platinum," we must not 

 reduce our weighings to sal-ammoniac (or ammonia, or nitrogen) by means of 

 factors calculated from the atomic weights concerned, but employ empirically 

 determined factors. 



According to our experiments, these factors are. 



Series, I. III. ^f g^ if 



A : C, -23944 -23842 -24121 



A : p, -54620 -54550 -54934 



Means of I. and III. 



A : C, = -23893 



A : p, . . . . = -54585 



We are painfully aware that our individual determinations of these factors 

 do not agree with one another as closely as we should wish. Yet we believe, 

 when used as such in an analysis, they will afford a very fair approximation to 

 the truth. 



Summary of Results. 



(1) The value Pt = 1948 (O -= 16), which Seubert deduced from his 

 analyses of chloroplatinates, is too low; his own analyses, if properly inter- 

 preted, show that the true value is by a considerable fraction of a unit 

 higher. 



(2) From our own experiments on chloroplatinate of potassium, it appears 

 that the true " Pt," though perhaps a shade below, lies close to, 195*5. This 

 value falls in perfectly well with Seubert's analyses; hence it, at present, is the 

 most probable value. 



(3) Taking " Pt " as the number which must be substituted for Pt in the 



