Sodium nitrate, NaNO₃

Immense deposits of sodium nitrate, NaNO₃, are situated in Chile, hence the name "Chile saltpetre." The local name is "Caliche." The origin of the deposits is a matter of dispute. The crude product is contaminated with clay and sand, and is purified by crystallization from water. An important impurity is sodium iodate, a valuable source of iodine. The chlorides can be decomposed by heating with nitric acid, hydrogen chloride being expelled.

Sodium nitrate is a white substance, and crystallizes in cube-like, doubly refracting rhombohedra isomorphous with calcspar. For its melting-point Haigh gives 306.8° C., Lorenz 310° C., Person 310.5° C., Bruni and Meneghini 312° C., Braun 314° C., Carnelley 316° and 319° C., and Carveth 318° C. For the freezing-point Schaffgotsch gives 313° C. The density is given by Krickmeyer as 2.267 at 20° C., by Haigh as 2.266 at 20° C., by Retgers as 2.265 at 15° C., by Brill and Evans as 2.175 at 13° C., and by Andreae as 2.261. Between 320° and 515° C. it is given, according to Lorenz, by the expression D = 2.12 – 0.0007t. For the specific heat between 27° and 59° C. Schuller found 0.2650, Regnault for the previously fused salt 0.2782, and Person for the liquid between 320° and 430° C. 0.41. The latent heat of fusion for 1 gram-molecule at 310.5° C. is given by Person as 5.5 Cal. The heat of formation from the elements is stated by Thomsen to be 111.25 Cal., and by Berthelot to be 110.7 Cal.; that from nitric acid and sodium hydroxide is given by Thomsen as 13.68 Cal., and by Berthelot as 13.5 Cal. For the heat of solution Thomsen gives. -5.0 Cal., and Berthelot between 10° and 15° C. - 4.7 Cal. The heptahydrate melts at -15.7° C.

The table summarizes the results obtained by the Earl of Berkeley10 in his work on the solubility of sodium nitrate:

Temperature, °C	0	10	20	30	40	50	60	70	80	90	100	119
Grams of NaNO3 in 100 grams of Water	73	80.5	88	96.2	104.9	114	124.6	136	148	161	175.5	208.8

Gerlach gives the boiling-point of the saturated solution in contact with the solid as 120° C., and its strength as 222 grams per 100 grams of water; the Earl of Berkeley and Applebey's value for the boiling-point is 120.20° C. at 760 mm.

In the fused state sodium nitrate is dissociated to the extent of 61.7 per cent., and its mean molecular refraction between 320° and 440° C. is 11.54.

The molecular electric conductivity of sodium nitrate between 321.5° and 487.3° C. is given by the formula

μ_t = 41.56+0.205(t - 300).

Sodium nitrate is a very deliquescent substance, and is therefore unsuited for the manufacture of explosives. It is employed in agriculture as a fertilizer, and by double decomposition with potassium chloride yields potassium nitrate. Large quantities are reduced to sodium nitrite, an important reagent in the manufacture of coal-tar dyestuffs.

References are appended to investigations of the molecular weight and surface tension of the fused salt; of the optical properties and electric conductivity; of such properties of aqueous solutions as boiling-point, density, viscosity, diffusion, specific heat, vapour-pressure, molecular weight of the dissolved salt, molecular depression of the freezing-point and elevation of the boiling-point, electric conductivity, and refractivity; of the solubility in organic solvents; and of the formation of double salts with potassium nitrate and sodium carbonate.