Lithium iodide, LiI

On evaporation of the solution obtained by the interaction of lithium carbonate and hydriodic acid, or barium or calcium iodide, lithium iodide crystallizes in the form of hydrates, a trihydrate, dihydrate, and monohydrate having been isolated. Above 300° C. the anhydrous salt is formed, but its action on glass and porcelain at high temperatures has prevented its preparation in the pure state. The boiling-point of the iodide is 1170° C., and the vapour-pressure in atmospheres corresponds with the expression

log p = -40300/4.57T+6.105.

The excessive solubility of the iodide is shown by the table -

Temperature, °C	0	10	20	30	40	50	60	70	80	99	120
Grams LiI in 100 g. H2O.	151	157	165	171	179	187	202	230	433	476	588

Other properties of dilute aqueous solutions have been studied by several investigators. The heat of formation in aqueous solution can be calculated like that of the chloride or bromide, and is given by the expression

[Li]+[I].+Aq.=LiI,Aq.+80.l Cal.;

and, since the heat of solution is 14.9 Cal., the heat of formation of the anhydrous iodide from lithium and iodine is expressed by

[Li]+[I]=[LiI]+65.2 Cal.

Lithium iodide resembles the chloride and bromide in the formation of double compounds with alcohols. At 25° C., 250.8 grams of the salt dissolve in 100 grams of ethyl alcohol. With propyl alcohol it yields a complex of the formula

LiI,4C₃H₇-OH.

Like the other halides, lithium iodide forms double salts with other metallic iodides, such as those of mercury and lead.