360 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Detection of Sodium, Caesium, and Rubidium. — Some 

 years ago W. C. Ball described some complex nitrites of bismuth, 

 prepared from the yellow liquid obtained by the interaction of 

 bismuth nitrate and sodium or potassium nitrite. Among these 

 were the triple salt Bi(N0 2 ) 3 .2NH 4 N0 2 .NaN0 2 , and the double 

 salt Bi(N0 2 ) 3 .3KN0 2 .H 2 0, both very soluble compounds. On 

 attempting to prepare similar rubidium and caesium derivatives, 

 it was found that dilute solutions of the nitrates of these metals 

 produced yellow, crystalline precipitates with the reagent 

 obtained from sodium nitrite and bismuth nitrate. These are 

 triple nitrites of bismuth, sodium, and rubidium or caesium, and 

 their formation serves as a very useful method of detecting these 

 metals in the presence of an excess of potassium. The reaction 

 for caesium is especially delicate. Furthermore, a reagent may 

 be prepared by the addition of a caesium salt to the product of 

 the reaction of bismuth nitrate and potassium nitrite, which 

 serves as a remarkably delicate test for sodium in producing a 

 precipitate of the same triple bismuth-sodium-caesium nitrite. 



The bismuth-sodium nitrite reagent is best prepared by dis- 

 solving 50 g. of pure sodium nitrite in 100 cc of water, neutral- 

 izing with nitric acid if necessary, and adding 10 to 20 g. of 

 powdered bismuth nitrate. The resulting orange-colored solution 

 must then be filtered and kept in a well-stoppered bottle, as it 

 absorbs oxygen and becomes turbid when exposed to the air. In 

 using this reagent to test for rubidium and caesium, the solution 

 to be tested is added to a large excess of the reagent acidified 

 with one or two drops of nitric acid to prevent the formation of 

 a basic bismuth salt. In all these tests it is better to use nitrates 

 or sulphates, rather than chlorides, on account of the tendency of 

 bismuth oxychloride to precipitate when concentrated solutions 

 of chlorides are used. The reagent gives a precipitate quickly 

 with a 0*5 per cent solution of rubidium. Only heavy metals 

 and caesium interfere with the test, which affords an easy method 

 for distinguishing rubidium from potassium, ammonium, lithium, 

 thallium, etc. The precipitate is bright yellow and crystalline, 

 and probably corresponds to the formula Bi(N0 2 ) 3 .'2RbN0 2 .- 

 NaN0 2 . The test for caesium with this reagent is still more 

 delicate, l cc of a 0*2 per cent solution of caesium nitrate giving an 

 immediate yellow crystalline precipitate with 4 or 5 CC of the 

 reagent. 



The reagent for sodium is prepared by dissolving 50 g. of 

 potassium nitrite in double its weight of water, neutralizing with 

 nitric acid, adding 10 g. of powdered bismuth nitrate, filtering, 

 adding a 10 per cent solution of caesium nitrate until the powdery 



