764 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. Notes on Isotopic Lead. — Frank Wigglesworth Clarke 

 has given an interesting discussion of the developments within 

 the past few years in regard to the forms of lead produced by 

 radioactive transformations. The forms of lead thus produced 

 are identical with ordinary lead in their distinctively chemical 

 properties, but they differ from it appreciably in atomic weight 

 and in specific gravity. Thus the lead from the purest uranium 

 minerals has an atomic weight fully a unit lower than that of 

 ordinary lead, while that from thorium minerals is nearly a unit 

 higher, and they are called isotopes of lead. Other cases of 

 isotopes are believed to exist in connection with the temporary 

 elements produced by radioactive transformations, but in no 

 other cases is there evidence of any variation in the atomic 

 weights of elements from different sources. In the case of ordi- 

 nary lead it has been found that samples from various localities 

 and different minerals give the same atomic weight within the 

 limits of experimental error, that is, between 207-20 and 207-22, 

 according to the results of Baxter and Grover. Samples of lead 

 from uranium minerals have given varying results, some as low 

 as 206-04 and 20609, while a thorite lead gave 207-77. Since 

 uranium minerals usually contain some thorium, and vice versa, 

 and since contamination with ordinary lead is possible, there is 

 some doubt about the actual atomic weights of these isotopes, 

 and the rather wide variations in the results obtained for the 

 atomic weights of radioactive lead is easily explained. 



The author criticizes the employment of the ratio between lead 

 and uranium as first used by Boltwood for calculating the age of 

 uranium minerals, chiefly on the ground that a part of the lead 

 present may be normal lead. Boltwood calculated the age of 

 Connecticut uraninite to be 410,000,000 years, and that of Cey- 

 lonese thorianite as 2,200,000,000 years. He criticizes the method 

 further from the fact that Becker in calculating the ages of 

 minerals from Llano County, Texas, found enormously different 

 ages for the same mineral from different analyses. For example, 

 two analyses of fergusonite by Mackintosh gave the ages 

 10,350,000,000 and 2,967,000,000 years. The author notes that 

 Barrell and others defend the use of the lead-uranium ratio for 

 determining the age of minerals, and admits that the subject is 

 still open to discussion. — Proc. Nat. Acad. Sci., 4, 181. h. l. w. 



2. The Recovery of Potash and Other Materials from Kelp. — 

 When the supply of German potash salts was cut off in 1914, 

 the kelp of the Pacific Coast of the United States attracted much 

 attention as a source of potash, and C. A. Higgins has recently 



