Rubidium nitrate, RbNO₃

The Rubidium nitrate, RbNO₃, is trimorphous, crystallizing in hexagonal, cubic, and bi-refractive forms, the transition-points in the order named being 161.4° C. and 218.9° to 219.3° C. The crystals are very hard, melt at 313° C., and have a density of 3.131 at 15° C. and 3.112 at 20° C. The molecular electric conductivity of rubidium nitrate between 318.8° and 493° C. is given by the formula

μ_t =33.51 + 0.145(t – 300).

The solubility in water is given in the table:

Solubility of Rubidium Nitrate

Temperature, °C.	0	10	20	30	40	50	60	70	80	90	100
Grams of RbNO3 per 100 g. of water.	19.5	33.0	53.3	81.3	116.7	155.6	200	251	309	375	452

A saturated solution containing 617 grams in 100 grams of water boils at 118.3° C. under a pressure of 734 mm. of mercury. In chemical properties the salt resembles potassium nitrate. It exhibits radioactivity. With nitric acid it yields acid nitrates, RbNO₃,HNO₃, melting at 62° C., and RbNO₃,2HNO₃, melting at 39° to 46° C.