COMPOUNDS OF POTASSIUM AND SODIUM. E29 
mostly of the nitrates of lime and magnesia which form in 
these beds. Refuse animal and vegetable matter putrefied 
in contact with calcareous soils produces nitrate of hme, 
which affords the nitre by reaction with carbonate of pot- 
ash. Old plaster lixivi ated affords about 5 per cent. his 
last method is much used in France. The nitric acid of 
the cavern nitrates comes from the atmosphere, which also 
consists of nitrogen and oxygen ; but the combination takes 
place through the agency of a peculiar kind of microscopic 
plant. 
Nitratine._-_Soda Nitre. Sodium Nitrate. Cubic Nitre. 
Rhombohedral ; 2: R=106° 33’. Also in crusts or efflo- 
rescences, of white. grayish atl ‘brownish colors. ‘Taste 
cooling. Soluble and very deliquescent. 
Composition. Na,O;N=Nitrogen pentoxide 63°5, soda 
36°5=100. Burns vividly on coal, with a yellow light. 
Diff. 1t resembles nitre (saltpetre), but deliquesces, and 
gives a deep yellow light when burning. 
Obs. In the district of Tarapaca, Northern Chili, the 
dry Pampa for an extent of forty leagues is covered with 
beds of this salt, mixed with gypsum, common salt, glauber 
salt, and remains of recent shells. 
It is used extensively in the manufacture of nitric acid. 
It is also used in making nitre by replacing the sodium by 
potassium. In 1866, one million quintals of this sult were 
exported from Chili. 
Natron._-_Hydrous Sodium Carbonate. Carbonate of Soda. 
Monoclinic. Generally in white efflorescent crusts, some- 
times yellowish or grayish. ‘Taste alkaline. Effloresces on 
exposure, and the surface becomes white and pulyerulent. 
Composition. Na,O3;C+10aq=Carbon dioxide 26°7, soda 
18°8, water 54°5=100. Effervesces strongly with acids. 
Diff. Distinguished from other soda salts by efferves- 
cing, and from trona, by efflorescing on exposure. 
Obs. This salt is found in solution in certain waters, 
from which it is crystallized in efflorescences by evapora- 
tion. Abundant in the soda lakes of Egypt ; also in lakes 
at Debreczin, in Hungary ; in Mexico, north of Zacatecas, 
and elsewhere. Sparingly dissolved in the Seltzer and 
Carlsbad waters. 
