SODA. 



197 



in solution in mineral springs, and is often one of the ingredients of sea water. In some 

 cases it accompanies the carbonate of soda, when its occurrence may be referred to the mu- 

 tual decomposition of common salt and sulphate of magnesia. This action is especially 

 observed at low temperatures : it is in winter that Glauber's salt is found in the greatest quan- 

 tity in certain lakes.* 



This salt, mixed however with various other saline matters, is found in the form of an efflo- 

 rescence on the limestone below the Genesee falls at Rochester, in Monroe county. It is also 

 held in solution by the water of the Longmuir spring, in the city of Rochester. 



NATRON. 



[From the desert of Natron, where it was formerly obtained.] 



Soda Carbonatee. Hauy. — Carbonate of Soda. Cleaveland and Phillips. — Hemiprismatic Natron. Jameson. 

 Hemiprismatisches Natron-Salz. Mohs. — Natron. Seudant, Shepard and Dana. 



Fig. 19. 



Fig. 20. 



(Fig. 19). 



Description. A saline substance, 

 usually occurrring effloresced and in 

 powder ; but it is easily crystallized 

 artificially, when it assumes the 

 form of the octahedron with a rhom- 

 bic base, truncated at the summit 

 The primary form, according to Haiiy, is that represented in Fig. 20. P on P 

 143° 8'; P onP' 113° 54'. 



Natron has an alkaline reaction, effervesces with acids, and is soluble in about two parts of 

 cold water. It gives the flame of alcohol a yellow tint, by which it can be distinguished from 

 carbonate of potash. The crystals of natron effloresce in the air ; those of trona do not. 



Composition. When entirely pure, it contains carbonic acid 32.30, soda 46.70, water 

 14.00, but it is almost always mixed with portions of sulphate of soda and common salt. Its 

 formula is NaCOa-|-Aq. 



Uses. This salt is largely employed in the manufacture of soap and glass, 

 prepared artificially by the decomposition of Glauber's salt. 



It is now 



localities. 

 This salt occurs in needleform efflorescing crystals on walls in the cities of New- York and 

 Albany, where it is probably produced by the reciprocal action of carbonate of lime and com- 

 mon salt. The fact that such a mutual decomposition does take place, was first proved by 

 Berthollet, who carefully examined the subject, and communicated the results of his observa- 



• Beudant. Truti EHmentaire dt Mmhalogit, I. 647. 



