722 
Proceedings of the Royal Society of Edinburgh. [Sess. 
critical study of the constant in question seemed altogether desirable. 
The work recorded in the following pages has extended over a period of 
four years. 
Historical. 
Berzelius * was the first to work upon the atomic weight of platinum. 
As early as 1826 he determined the per cent, of platinum in platinous 
chloride, and from these analyses a value of 193T6 is obtained for the 
atomic weight. Two years later, j- by decomposing potassium chloro- 
platinate in hydrogen, he obtained data from which the atomic weight of 
platinum can be calculated by several ratios. The values calculated from 
these ratios vary between 195*4 and 196*6, giving a mean of 195*90. 
A report of some work by Andrews f appeared in 1852, but a detailed 
statment of his experiments is lacking. He worked with potassium 
chloroplatinate, decomposing it by means of zinc and water. After dis- 
solving the excess of zinc and filtering, the chlorine in the filtrate was 
estimated and the platinum was dried and weighed. From three determina- 
tions we have the values 197*9, 197*7, and 198*1 for the atomic weight, or 
a mean value of 197*9. 
Previous to the publication of Seubert’s § determinations in 1881 the 
atomic weight of platinum was supposed to lie above that of gold. This 
investigation, however, showed that platinum had an atomic weight several 
units below that of gold. He studied both potassium and ammonium chloro- 
platinate, preparing these salts with great care, and decomposing them in a 
stream of hydrogen. The resulting hydrochloric acid was in some cases 
absorbed in water or silver nitrate solution, and the chlorine estimated as 
silver chloride. From the weight of the original salt, the weight of 
platinum residue, of potassium chloride, and of chlorine lost upon ignition, 
several independent ratios are obtained, from which the value sought can 
be calculated. 
Three different samples of ammonium chloroplatinate gave the following 
mean values, reducing the weight to the vacuum standard, and assuming 
that chlorine = 35*46, nitrogen — 14*01, hydrogen = 1*008, bromine = 79*92, 
silver = 107*88, and potassium = 39*11. 
I. From the ratio (NH 4 ) 2 C1 6 : Pt . . . . 195*12 
II. „ „ (NH 4 ) 2 C1 6 : Pt . . . . 194*47 
III. „ „ (NH 4 ) 2 C1 6 : Pt . . . . 195*47 
* Poggend, Annalen , viii. 177 (1826). t Ibid., xiii. 468 (1828). 
X British Assoc. Report , 1852. § Ber. JUeutsch. Ghem. Gesell., xiv. 865 (1881). 
