Chemistry and Physics, 459 



2RbCl. HgCl 2 . H 2 

 , 3RbC1.2lIgCl„.2H 2 



RbCl. HgCl 2 \ H 2 

 3RbCI.4HgCl a . H 2 



RbC1.5HgCl 3 . 



It is interesting to observe that only the last member of this 

 series corresponds to one of the five caesium-mercuric chlorides 

 that exist, viz. : 



SCsCl. HgCl 2 



2CsCl. HgCl 2 



CsCl. HgCl 2 



CsC1.2HgCl 2 



CsC1.5HgCl 2 . 



There are two corresponding salts in the potassium and rubidium 

 series, but the slight analogy existing between double salts of. 

 such closety related metals as caesium and rubidium is remarkable. 

 — Amer. Chem. Jour., xxxv, 236. h. l. w. 



3. The Atomic Weight of Tantalum. — The accepted atomic 

 weight of this element, 183, depends solely upon Marignac's 

 results obtained in 1865 by analyses of the compound K 2 TaF 7 . 

 Since these results are subject to some uncertainty from various 

 causes, Hinrichsen and Sahlbom have made some new determi- 

 nations of this atomic weight. They were unable to obtain con- 

 cordant results by the method of Marignac, but they had, 

 apparently, better success by determining the weight of Ta 2 5 

 produced by heating the metal in oxygen. The metal was 

 obtained from Siemens and Halske, who now prepare it for com- 

 mercial purposes, and no impurities could be found in the mate- 

 rial used. The results of five determinations made in this way 

 indicate an atomic weight of 181, which is two units lower than 

 the accepted one. The results varied'from 180*59 to lSl^T. It 

 may be mentioned that this atomic weight adapts itself to Men- 

 deleeff's periodic system somewhat better than the old one, since 

 it is three units lower than tungsten, 184. — Berichte, xxxix, 2600. 



h. l. w. 



4. The Isomorphism of Northupite and Tychite. — The octa- 

 hedral mineral tychite, 2MgC0 3 .2Na 2 C0 3 .Na 2 S0 4 , was described 

 by Penfield and Jamieson in this- Journal of September, 1905, 

 having been found among exactly similar crystals of northupite, 

 2MgCO,.2Na a C0 3 .2NaCl, from Borax Lake in California. In con- 

 nection with the description of tychite, its artificial preparation 

 was also carried out. A. de Schulten, who had previously pre- 

 pared northupite artificially, has now succeeded in making crops 

 of crystals which appear to contain both chloride and sulphate in 

 the same individuals, thus indicating that the two compounds are 

 perfectly isomorphous. He finds that the tychite is much more 

 stable than the northupite. — Comptes Rendus, clxiii, 403. 



h. l. w. 



