284 METALS AND THEIR COMBINATIONS. 



Barium oxide, BaO, is made by heating barium nitrate, Ba(N0 3 ) 2 , which 

 itself is made by dissolving barium carbonate in nitric acid. 



Barium salts are poisonous ; antidotes are sodium and magnesium sulphates. 



Tests for barium. 

 (Use the reagent solution of barium chloride.) 



1. The reactions of barium salts with soluble carbonates, oxalates, 

 and phosphates are analogous to those of solutions of calcium salts. 



2. Add dilute sulphuric acid or solution of a sulphate : a white 

 precipitate of barium sulphate, BaSO 4 , is produced immediately, even 

 in dilute solutions. The precipitate is insoluble in all diluted acids. 



3. Add calcium sulphate solution : a white precipitate, insoluble in 

 all diluted acids, is formed immediately (compare with test 2 under 

 Strontium). 



4. Add potassium chromate or dichromate solution : a pale-yellow 

 precipitate of barium chromate, BaCrO 4 , is formed, insoluble in acetic 

 acid, but soluble in hydrochloric or nitric acid. 



5. Volatile barium compounds color a Buusen flame yellowish 

 green (see remarks under test 6 for calcium). 



Tests 3, 4, and 5 give conclusive proof of barium. Insoluble com- 

 pounds are treated as directed under tests for calcium. 



Radium, Ha = 223.3, This element, discovered in 1899, has been men- 

 tioned in the article on radio-activity, page 85. While radium is closely 

 related to barium it has not been found in the native barium compounds, except 

 when they occur associated with uranium as in pitch-blende, an ore from which 

 uranium compounds are extracted. This ore contains, however, but 0.1 gramme 

 of radium in 1000 kilograms, which is equal to 0.00001 per cent. The residue 

 left, after the uranium has been eliminated, contains from 2 to 3 times as much 

 radium as the original ore. From 1000 kilograms of this residue 10 to 15 kilo- 

 grams of radiferous barium salt (chloride or bromide) are extracted, and from 



QUESTIONS. Which metals form the group of the alkaline earths, and in 

 what respect do their compounds differ from those of the alkali-metals? How 

 is calcium found in nature? What is burned lime; from what, and by what 

 process is it made, and how does water act on it? What is lime-water; how 

 is it made, and what are its properties? Mention some varieties of calcium 

 carbonate as found in nature, and how is it obtained by an artificial process 

 from the chloride ? What is Plaster-of-Paris, and what is gypsum ; what are 

 they used for? State composition and mode of manufacturing bleaching- 

 powder ; what are its properties, and how do acids act upon it ? What is bone- 

 black, bone-ash, acid phosphate, and precipitated tricalcium phosphate ? How 

 are they made? Give tests for barium, calcium, and strontium ; how can they 

 be distinguished from each other ? Which compounds of barium and stron- 

 tium are of interest, and what are they used for? 



