Chemistry and Physics. 79 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. A New Intermediate Product in Thorium. — It is well 

 known that the radio-activity of ordinary thorium has been attrib- 

 uted by Hadn to radio-thorium, an element so closely related 

 chemically to inactive thorium that the separation of the two 

 presents the greatest difficulties. Boltwood and Dadourian of 

 Yale University both found that the activity of thorium minerals 

 depends directly upon the amount of thorium in them, from which 

 it follows that radio-thorium must be a product derived from ordi- 

 nary thorium. The same investigators found, however, that 

 commercial thorium nitrate possessed an activity less than one- 

 half as great as it should have, according to the activity of the 

 minerals. This striking result led at first, to the belief that radio- 

 thorium must have been separated to a large extent in the process 

 of manufacturing the salt, in spite of the fact of the well-known 

 difficulty of this separation. Hahn has now explained the cause 

 of the low x*adio-activity of the artificial salt in a very ingenious 

 and satisfactory manner. Upon examining samples of thorium 

 nitrate, which had been kept for various lengths of time, he found 

 that products recently made from monazite gave the activity to 

 be expected according to the amounts of thorium in them, while 

 older preparations gave a much diminished activity. The activ- 

 ity appears to diminish for about three years, then to remain 

 neai'ly constant for a considerable periQcl, and finally to increase 

 gradually. Hahn explains this behavior by supposing that a prod- 

 uct intermediate between thorium and radio-thorium, which emits 

 no a-particles, is separated in the technical production of thorium 

 nitrate ; the radio-thorium, which appears to have a period of decay 

 of about two years, gradually disappears until a sufficient amount 

 of the more slowly formed and more slowly decomposing inter- 

 mediate substance has been formed to cause the radio-thorium to 

 increase towards equilibrium. At present the data are uncertain, 

 but Hahn estimates that the period of existence of the interme- 

 diate product is about 7 years, and that equilibrium would be 

 reached in about forty years. Hahn believes that he has positive 

 proof of the existence of the intermediate product in some prep- 

 arations which, while containing no appreciable quantity of tho- 

 rium, are increasing in activity and are producing radio-thorium. 

 Mesothorium is the name suggested for the intermediate body. — 

 Berichte, xl, 1462. h. l. w. 



2. The Interference of Fluorides with the Precipitation of 

 Alumina. — For the determination of the bases in silicates, the 

 method sometimes used is the treatment of the substance with 

 hydrofluoric and sulphuric acids, followed by evaporation and 

 heating until fumes of sulphuric acid come off, in order to remove 



