Chemistry and Physics. 57 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. Uranium Hexafluoride. — Since no hexavalent halogen com- 

 pound of uranium has been previously prepared, the preparation 

 of the fluoride UF 6 by Ruff and Heinzelmann is of considerable 

 interest. It appears that a supposed previous preparation of this 

 compound by Ditte was not founded on fact. Three methods 

 were worked out for the preparation of the compound : 1. The 

 action of fluorine upon uranium pentachloride ; 2. The action of 

 anhydrous hydrofluoric acid upon uranium pentachloride ; 3. The 

 action of fluorine upon metallic uranium or uranium carbide. 

 According to the first two methods the product consisted of a 

 mixture of two fluorides, according to the equations 



2UC1 5 + 5F, =UF 4 + UF R + 5Cl 2 and 

 2U Cl 5 + 5H 2 F 2 = UF 4 + ITF 6 -f 10HC1. 



The higher fluoride, being very volatile, is easily separated from 

 the other one, but when prepared according to the second method 

 it was separated only with considerable difficulty from the excess 

 of anhydrous hydrofluoric acid. The action of pure fluorine 

 upon metallic uranium gave, as Moissan had shown, a product 

 consisting chiefly of the tetrafluoride, but it was found that when 

 a little chlorine was mixed with the fluorine, complete conversion 

 into hexafluoride took place. The chlorine appears to act as a 

 catalytic agent in this case. 



Uranium hexafluoride is a very volatile, pale yellowish, crystal- 

 line solid which boils at 55° C. at atmospheric pressure. Its 

 melting-point, 69*5° C, lies above its boiling-point, so that a pres- 

 sure of about two atmospheres is required to melt it. The sub- 

 stance is extremely reactive ; it is very sensitive toward moisture; 

 it reacts with hydrogen even when cold ; the chief product of its 

 reduction appears to be uranium tetrafluoride. Its reaction with 

 sulphur is particularly interesting, as it seems to give a new gase- 

 ous fluoride of sulphur. — Zeitschr. anorgan. Chem., lxxii, 63. 



II. l. w. 



2. The Atomic Weight of Extra-terrestrial Iron. — Since, as 

 far as is known, atomic weight determinations have always in the 

 past been carried out with material of terrestrial origin, it seemed 

 worth while to Baxter and Thorvaldson to make such a deter- 

 mination on an element of meteoric origin. Iron was selected as 

 the subject of investigation, and for the purpose a piece of a 63 lb. 

 meteoric iron found in 1903 near Cumpas, Mexico, was used. 

 After an elaborate series of purification operations, ferrous bro- 

 mide was prepared and analyzed according to a method that had 

 been previously employed by the authors in connection with ter- 

 restrial iron. The results indicated no appreciable difference 



