Praseodymium chloride, PrCl₃

Praseodymium chloride, PrCl₃, is a green, hygroscopic solid which fuses to a green liquid. The density is 4.020 at 25° C. (Baxter and Stewart).

From aqueous solution the heptahydrate, PrCl₃.7H₂O, separates in large, green crystals of density 2.25 at 15° (Scheele). The crystals melt at 111° C. (Baxter and Stewart). When dried over sulphuric acid, the heptahydrate rapidly passes into the hexahydrate, PrCl₃.6H₂O, which is slowly dehydrated to the trihydrate, PrCl₃.3H₂O. The monohydrate is also known. At 13.8°, 100 parts of water dissolve 103.9 parts of anhydrous chloride or 334.2 of the heptahydrate, the solution being in equilibrium with the heptahydrate (Matignon). The concentrated aqueous solution dissolves considerable quantities of rare earth oxalates.

Praseodymium aurichloride, PrCl₃.AuCl₃.10H₂O, forms yellow crystals of specific gravity 2.60 and is readily soluble in water. The chloroplatinate, PrCl₃.PtCl₄.12H₂O, is also a yellow crystalline salt, of density 2.41 at 16°.