266 METALS AND THEIR COMBINATIONS. 



heat it loses water, and is converted into pyrophosphate, which, dis- 

 solved in hot water and crystallized, forms the official salt. The 

 chemical change taking place is this : 



2(Na 2 HP0 4 ) Na 4 P 2 7 + H 2 O. 



The normal sodium phosphate, Na 3 PO 4 , is known also, but it is not a very 

 stable compound, being acted upon even by the moisture and carbon dioxide 

 of the air, with the formation of sodium carbonate and disodium hydrogen 

 phosphate, thus : 



H 2 + C0 2 = 



Sodium nitrate, Sodii nitras, NaNO 3 = 84.45 (Chile saltpeter, 

 Cubic niter). Found in nature, and is purified by crystallization. 

 The crystals are transparent, deliquescent, and readily soluble. 



Sodium nitrite, Sodii nitris, NaNO 2 = 68.57, is formed by heating the nitrate 

 to a sufficiently high temperature to expel one-third of the oxygen ; or, better, 

 by treating the fused nitrate with metallic lead, which latter is converted into 

 oxide. The sodium nitrite which is formed is dissolved and purified by crystal- 

 lization. 



Sodium borate, Sodii boras, Na 2 B 4 O 7 .lOH 2 O = 379.32 (Borax). 

 This salt occurs in Clear Lake, Nevada, and in several lakes in Asia. 

 It is manufactured by adding sodium carbonate to the boric acid 

 found in Tuscany, Italy. It forms colorless, transparent crystals, 

 but is sold mostly in the form of a white powder. It is slightly 

 efflorescent, is soluble in 16 parts of cold, and in 0.5 part of boiling 

 water ; insoluble in alcohol, but soluble in one part of glycerin at 

 80 C. (176 F.). When heated, borax puffs up, loses water of 

 crystallization, and at red heat it melts, forming a colorless liquid 

 which, on cooling, solidifies to a transparent mass, known as fused 

 borax, or borax glass. Molten borax has the power to combine with 

 metallic oxides, forming double borates, some of which have a char- 

 acteristic color, for which reason borax is used in blow-pipe analysis. 

 Borax has antiseptic properties, preventing the decomposition of some 

 organic substances. 



A solution of borax is alkaline and has no action on carbonates or bicarbon- 

 ates, but if an equal volume of glycerin is added to the solution, it becomes 

 strongly acid and decomposes carbonates and bicarbonates with effervescence. 

 This behavior has an important bearing in prescription writing. On diluting 

 the glycerin mixture strongly with water, the alkaline reaction returns. 



Other sodium salts which are official are sodium hypophosphite, 

 NaPH 2 O 2 + H 2 O; bromide, NaBr; iodide, Nal ; chlorate, NaClO 3 . 



