Boltwood

Boltwood BB (1907) Note on a new radio-active element. Amer J Sci 24 370-372... 

The discovery of the decay chain, of course, started with the seminal work of Marie Curie in identifying and separating Ra. Through the work of the Curies and others, all the members of the decay chain were identified. An important milestone for geochronometrists was the discovery of °Th (called Ionium) by Bertram Boltwood, the Yale scientist who also made the first age determinations on minerals using the U-Pb dating method (Boltwood in 1906 established the antiquity of rocks and even identified a mineral from Sri Lanka-then Ceylon as having an age of 2.1 billion years )... 

Shortly thereafter, Boltwood recognized that the Pb content of minerals increases with age and it became clear that Pb was the final product of radioactivity. Boltwood was also responsible for adding another substance to the decay series through his discovery of ionium ( °Th), and therefore for linking the U and Ra decay chains (Boltwood 1907). The discovery of initially known as UrII, followed in 1912. 

In 1900 Sir William Crookes prepared a solution containing a uranium salt and a small amount of a ferric salt. When he added to this an excess of a solution containing ammonium hydroxide and ammonium carbonate, he found that the resulting ferric hydroxide precipitate was intensely radioactive. After studying the radioactive properties of the substance which precipitates with the iron, he said, For the sake of lucidity the new body must have a name. Until it is more tractable I will call it provisionally UrX—the unknown substance in uranium (30). It is now known as uranium Xi. H. N. McCoy and W. H. Ross, B. B. Boltwood, and R. B. Moore and H. Schlundt found independently that there are two uraniums, uranium 1 and uranium 2 (12, 48, 81, 108, 109, 110). 

In 1904 B. B. Boltwood, H. N. McCoy, and R. J. Strutt proved independently that radium is produced by spontaneous transmutation of uranium (107). Three years later Boltwood discovered an element which he named ionium and which he found to be the parent substance of radium (39). Professor Boltwood had acquired a broad cosmopolitan education in Munich, Leipzig, Manchester, and New Haven, and was a skilled laboratory technician, a sympathetic teacher, and a polished gentleman with a certain courtliness of manner. He proved that there is a genetic relationship between uranium, ionium, and radium (13). Ionium was discovered independently at about the same time by Otto Hahn and by Willy Marckwald (14, 73, 77). 

Bertram Borden Boltwood, 1870-1927. Professor of chemistry and physics at Yale University. Discoverer of the radioactive element ionium, the parent of radium. Ionium was discovered independently at about the same time by Hahn and by Marckwald. 

Since the radioactivity of thorium salts is smaller than that of the minerals, B. B. Boltwood (93) thought that some of the radiothorium must have been lost during the purification process. On the assumption that radiothorium was formed directly from thorium, he computed that the half-life period of the former ought to be at least six years, whereas... 

Editor s outlook. Bertram Borden Boltwood, . Chem. Educ., 6, 602-4... 

Twentieth Century Demargay discovers europium. Rutherford and Soddy discover thorium X. B. B. Boltwood, H. N. McCoy, and J. W. Strutt prove independently that radium is produced by spontaneous transmutation of uranium. 

Boltwood discovers ionium. This element was independently discovered by Hahn and Marckwald. 

The American scientist B. B. Boltwood appreciated as early as 1907 that radioactive decay can tell us about the age of the Earth. The best estimate until that time was around 98 million years, which Lord Kelvin deduced in the 1860s by considering how long it would take for the hot core to cool down. Boltwood calculated that the planet could be as much as two billion years old. The current estimate of more than twice this value is supported by a host of other radiometric methods which look at the relative abundances of parent and daughter isotopes in radioactive decay chains. 

On Harkins, see R.S. Mulliken, William Draper Harkins, 1873-1951, Biographical Memoirs of Members of the National Aca-damy of Science 47 (1975) 49-81 and G. B. Kauffman, William Draper Harkins (1873-1951) A controversial and neglected physical chemist, Journal of Chemical Education 62 (1985) 758-761. In a letter to Bertram Boltwood of February 28, 1921, Rutherford described Harkins as moderately sound and a man of intelligence, but added that I wish he did more experimenting and spent less time in theorising and in endeavouring to cover every possible idea. Quoted in L. Badash (ed.), Rutherford and Boltwood Letters on Radioactivity (New Haven, 1969), 343. 

The latter assumption is now seen to be extremely doubtful for,the varying atomic weights prove that more than one kind of lead must be considered. Thorium lead especially must be taken into account, for many uraninites contain it, and in thorianite the percentage of thoria is more than five times that of uranium oxide. The ratio of lead to its parent elements is therefore much less than Boltwood assumed, and the calculated age of thorianite is vastly reduced. Boltwood, however, doubted the derivation of lead from thorium, a fact which was not definitely known at the time his paper was written. The evidence of the atomic weights is also much later. 

Furthermore, the doubtful applicability of Boltwood s method to chronological measurements has been shown by G. F. Becker 12 who applied it to the analyses of rare-earth minerals from one locality in Llano County, Texas. The figures given by Becker are as follows ... 

I. Physical Chemistry for Beginners, Van Deventer. Translated by Boltwood. John Wiley Sons, New York. 154 pp. 1.50. 

It was observed by Boltwood in comparing the ionising power of uranium, deprived as far as possible of all its dismtegration products, with the ionising power of the other a-radiating members of the series, that the uranium expelled twice the number of a-particles given out by any of the other members in equilibrium -tt ith it. This was confirmed by... 

Ionium, the product of uranium II and the immediate parent of radium, was isolated by Boltwood in 1907. ... 

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