Platinum, atomic weight

Occurrence and History of Platinum--Proparatioi) -Punlioulimi Physical Properties—Volatilisation -Diffusion of Cases Solubility of (laMes Chemical Properties - -Catalytic Activity -Passivity Crystalline Platinum —Colloidal Platinum — Platinum Black Platinum Mpongo Explosive Platinum —Atomic Weight — Uses Buhstitutes Alloys Platinum Amalgam. 

Then, since Atomic Weight of platinum = 195 2, if g g. platinum is obtained from G g. chloroplatinate,... 

The molecular weight of the salt is calculated fiom the weight w of the platinum, and IV of the salt, accoidmg to the foiniula (the atomic weight of platinum being 195)... 

The alkali chlor-ruthenates are isomorphous with the chlor-platinates, and therefore, by the application of llitscherlich s Law, they must be assumed to contain, like the platinum derivatives, one atom of ruthenium, their generic formula being M,RuC16. Similarly, ruthenium dioxide is isomorphous with cassiterite, SnO,. and with rutile, TiCL. from which it may be concluded that its formula is RuO.,. Analyses of these compounds indicate that the atomic weight of ruthenium is 101-7. 

A study of the chemical properties of iridium and its compounds shows that, whilst closely resembling platinum in many respects, it forms a fitting link between that element and osmium. With an atomic weight intermediate in value between 190-9 (at. wt. of osmium) and 195-2 (at. wt. of platinum), iridium falls into a suitable position in the Periodic Table where these analogies are recognised. 

Atomic Weight.—Approximate Value.—Several lines of argument lead us to the conclusion that the atomic weight of platinum is approximately 195, and not a multiple or submultiple of this amount. The more important of these may be summarised as follows ... 

The specific heat of platinum between 0° and 100° C. is 0-0323. Assuming a mean atomic heat of 6-4, application of Dulong and Petit s Law leads to the value 198 for the approximate atomic weight of platinum. 

Exact Value.—The first determination of the atomic weight of platinum was made by Berzelius in 1826.3 From the analysis of platinous chloride he found Pt = 194-7. Two years later he published his determination of the composition of potassium chlor-platinate4 6-981 parts of the salt lost 2-024 of chlorine when ignited in hydrogen, leaving a residue containing 2-822 of platinum and 2-135 of potassium chloride. Hence ... 

These results are now known to be extremely high, but until 1881 the accepted figure for the atomic weight of platinum rested entirely upon them, and they appeared to be corroborated by some analyses published by Andrews 5 in 1852. 

In 1881 Seubert,6by his analyses of ammonium and potassium chlor-platinate, showed that the atomic weight of platinum approaches the... 

The results of Seubert and Halberstadt have now been supplanted by the more modern work of Archibald, so that it will suffice to quote the ratios that they established and the values for the atomic weight of platinum deduced from them.3... 

It will be immediately obvious that such complete analyses, if concordant, afford valuable information regarding the purity of the potassium chlor-platinate. Nine values for the atomic weight of platinum may be deduced from each experiment by calculation from the following ratios ... 

The results of Archibald thus furnish data for twenty-eight ratios, from which twenty-eight values for the atomic weight of platinum may be deduced. The extreme difference between these values is only... 

The solubilities of the alkali brom-platinates in water and dilute hydrobromie acid decrease with increasing atomic weight of the alkali metal. The solutions obtained are red in colour, but turn yellow on dilution with water. Hydrazine hydrate decomposes them with ease, metallic platinum being deposited and nitrogen evolved. 

The Grouping of Elements into Triads—Atomic Weights of the Elements— General Properties of tho Elements—Comparative Study of Iron, Cobalt, and Nickel—Their Position in tho Periodic Table—Comparative Study of Iron, Ruthenium, and Osmium—Comparative Study of Cobalt, Rhodium, and Iridium—Comparative Study of Nickel, Palladium, and Platinum. 

---