Chemistry and Physics. 243 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Atomic Weight of Iodine. — A series of careful deter- 

 minations of this constant has been carried out by G. P. Baxter 

 of Harvard University. The ratios of silver to silver iodide, 

 silver to iodine, and silver iodide to silver chloride were found in 

 making these determinations, and the average of very closely 

 agreeing results by the three methods were 126*973, 126-977 and 

 126-975, where oxygen as 16 is taken as the basis. Several 

 other investigators — Scott, Ladenburg, and Kothner and Aeuer — 

 have recently obtained results upon the same atomic weight 

 which agree almost exactly with those of Baxter ; hence it 

 appears certain that the atomic weight 126*85 for iodine, which 

 has been accepted for many years on the authority of Stas and of 

 Marignac, is somewhat lower than the truth. In spite of his 

 wonderful skill, it seems that Stas was not quite infallible in his 

 atomic weight determinations. The international committee on 

 atomic weights, in the table for 1905, has adopted the value 

 126*97 for the atomic weight of iodine, when oxygen is 16, and 

 the value 12601, when hydrogen is taken as unity. Both of 

 these numbers, it may be noticed, are curiously close to being 

 confirmations of Prout's old hypothesis, which requires, practi- 

 cally, that the atomic weights should be whole numbers. — Zeitschr. 

 anorgan Chem., xliii, 14. h. l. w. 



2. Double Silicides of Aluminium. — Manciiot and Kieser 

 have obtained the crystalline compounds Cr 2 AlSi 3 and Cr 2 AlSi 4 by 

 the fusion of chromium compounds with an excess of aluminium 

 in the presence of potassium silicofluoride, and treatment of the 

 resulting metallic mass with an acid in order to dissolve the 

 aluminium. The compound, Cr 2 AlSi 3 , forms beautiful slender 

 crystals of hexagonal habit, which are opaque, with a strong 

 metallic luster and white color. The compound is very inactive 

 with most chemical agents. It is insoluble in acids, except 

 hydrofluoric acid ; it remains bright when heated in a stream of 

 oxygen, and is not attacked by fusion with potassium bisul- 

 phate ; but it readily decomposes by fusing with alkalies. The 

 other compound was obtained in 'a similar way in the presence of 

 a larger amount of silicon. It forms smaller crystals, is some- 

 what harder, but otherwise it is like the first compound in its 

 properties. These compounds are the first double silicides to be 

 described. — Ann. der Chem., cccxxxvii, 353. h. l. w. 



3. Europeum. — This element, occurring in very small quanti- 

 ties among the rare earths and coming between samarium and 

 gadolinium, was described by Demarcay several years ago. 

 Urbaijst and Lacombe have recently confirmed the existence of 

 the earth. They used 610 g. of oxides representing the whole of 

 the europeum group of earths from about 500 kilos of monazite 



