NITRATES OF EARTHS. 485 



NITRATES OF THE EARTHS. 



General characters. 



1. Similar to those of the nitrates of the alkalies, but their action 

 on ignited combustible bodies is less vigorous ; they rather scintillate 

 than deflagrate on burning coals, but are eventually decomposed both 

 by heat and by hot combustibles. 



2. In some of them, as the nitrates of strontia and baryta, the 

 acid is decomposed at once into nitrogen and oxygen, without the 

 formation of a nitrite ; the base being left behind. 



3. Sulphuric acid evolves the nitric acid. 



4. Only two of the earthy nitrates* are found native, the rest be- 

 ing formed by art. 



NITRATE OF BARYTA. 



1. DISCOVERY. First formed by Scheele and Bergman, in 

 1776. 



2. PREPARATION. 



(a.) By decomposing the carbonate of baryta, native or artificial, by 

 the nitric acid, diluted with from 8 to 16 times its volume of water ; 

 the effervescence is moderate. 



(b.) By decomposing, by the nitric acid, the artificial hydro-sulphu- 

 ret of baryta, formed from the decomposition of the sulphate by char- 

 coal ; or, a carbonate may first be formed by precipitating the baryta 

 from the solution of the sulphuret by the carbonate of an alkali, and 

 then this may be decomposed by nitric acid. 



3. PROPERTIES. 



(a.) Crystals are easily obtained from the evaporated solution ; 

 primitive form, the octahedron sometimes in brilliant triangular 

 plates, with truncated angles ; sometimes grouped in stars. 



(b.) Sp. gr. 2.9. Taste, sharp and acrid. 



(c.) Insoluble in alcohol, but soluble in 12 parts of water at 60, 

 and in about 3 or 4 at 212. Least soluble of all the nitrates ; nitric 

 acid being poured into a concentrated solution of muriate of baryta, 

 causes a precipitate of the nitrate which more water redissolves. 



Solution of nitrate of baryta should not cause a precipitate with 

 nitrate of silver. 



!d.) Air produces little change upon this salt, 

 e.) Decrepitates and feebly scintillates on burning coals, 

 (f.) Decomposed by ignition in a crucible, and affords pure 

 baryta,^ by a theory already explained. If decomposed in a porce- 



* Those of lime and magnesia. 



t If the heat is urged too far, it vitrifies in an earthen crucible. 



