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Atomic Weight of Strontium, history

Approximate Atomic Weight

The equivalent of strontium in the majority of its compounds is 44. Its properties indicate a position in the Periodic Table in the alkaline earth group, and, therefore, a valency of 2, making the atomic weight about 88. Glascock's value for the specific heat, 0.0742, indicates, according to Dulong and Petit's Law, an approximate atomic weight of 86.

Exact Atomic Weight

Berzelius, in his atomic weight table for 1814, gave a value for the atomic weight of strontium which, when referred to oxygen as 16, becomes 89.4, and is probably founded on the early analyses of Klaproth. The first recorded determination is that of Stromeyer, who measured the volume of carbon dioxide evolved by strontium carbonate and found an atomic weight of 87.3.

Richards made fresh determinations in 1905. As the mean of four titrations, he found that the ratio of a certain weight of silver to the weight of strontium chloride required to precipitate it is 100: 73.477. This gives a value of 87.620.

Finally, in 1910, Thorpe and Francis carried out a number of determinations with salts purified by extensive recrystallisations. Their results are recorded in the table on the following page.

The International Commission on Atomic Weights for 1910 adopted the value

Sr = 87.63,

which is still retained (1925).
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