Lithium chloride, LiCl

The anhydrous salt is obtained by evaporating to dryness in a current of hydrogen chloride or in presence of ammonium chloride the solution formed by dissolving the carbonate in hydrochloric acid, or decomposing the sulphate with barium chloride. Bogorodsky has isolated three hydrates: at very low temperatures the trihydrate, LiCl,3H₂O, is deposited in small needles; at -15° C. the dihydrate, LiCl,2H₂O, crystallizes in cubes; and at 12.5° C. octahedra of the monohydrate, LiCl,H₂O, are formed. At about 98° C. the anhydrous salt separates.

Various values are given for the melting-point of the chloride. Schemtschushny and Rambach found 614° C., Richards and Meldrum 613° C., Korreng and also Schaefer 609° C., Haigh 607° C., Huttner and Tammann 605° to 607° C., Wartenberg and Schulz 606° C., Hachmeister 605° C., Carnelley 602° C., Guntz 600° C., and Ramsay 491° C. The boiling-point is 1382° C., and the vapour-pressure in atmospheres corresponds with the expression

log p = - 37200/4.57T+4.923.

At white heat it volatilizes completely in a current of hydrogen chloride. The specific heat of the anhydrous salt at 13° to 97° C. is 0.2821, and its density at 20° C. is 2.068.

Lithium chloride is a very deliquescent, white substance of saline taste, and is excessively soluble in water. Kremers found that the solubility increases with rise of temperature. His values are given in the table:

Temperature, °C	0	20	65	80	96	140	160
Grams LiCl in 100 g. H2O	63.7	80.7	104.2	115	129	139	145

Solubility curve of lithium chloride (LiCl).

His results have been graphically represented by Auerbach and Brislee, the two breaks in the curve near 20° C. and 100° C. corresponding with the transition-temperatures of the individual hydrates. The three portions of the curve correspond with the solid phases LiCl,2H₂O, LiCl,H₂O, and LiCl. The break on the dotted portion of the curve at -15° C. represents the transition-point of the trihydrate, LiCl,3H₂O. A saturated solution of the chloride in contact with the solid phase boils at 168° C.

The solubility of lithium chloride has also been investigated by Gerlach, whose results are given in the table:

Temperature, °C	0	10	20	30	40	50	60	80	100
Grams LiCl in 100 g. H2O	67	72	78.5	84.5	90.5	97.0	103.0	115.0	127.5

References to work on the physical properties of aqueous solutions of lithium chloride are appended.

Solutions of lithium chloride resemble water in their power of absorbing ammonia, complex ammonia compounds being formed. The anhydrous lithium halides also absorb ammonia, Bonnefoi having prepared a series of compounds such as LiCl,NH₃, LiCl,2NH₃, LiCl,3NH₃, and LiCl,4NH₃. On heating, the ammonia is expelled, leaving the lithium chloride in a very porous condition, in which it combines readily with organic amines to form a series of analogous derivatives of complex type.

Lithium chloride is soluble in many organic solvents: among them are alcohols, such as methyl alcohol, ethyl alcohol, higher alcohols, and glycerol; aldehydes and ketones, such as acetaldehyde, paraldehyde, and acetone; fatty acids, such as formic acid and acetic acid; nitriles, such as acetonitrile and propionitrile; phenol; and bases, such as pyridine. Solution is sometimes accompanied by evolution of heat and formation of compounds, examples of those isolated being

LiCl,3CH₃OH, LiCl,4C₂H₅OH, LiCl,(CH₃)₂CO, LiCl,2C₂H₅N.

Kahlenberg and Krauskopf have utilized the solubility of lithium chloride in anhydrous pyridine in separating it from the chlorides of the other alkali-metals and barium, these salts being insoluble.

The degree of dissociation in acetone and pyridine is very small, but in formic acid it is of the same order as in water. For the alcohols and acetaldehyde it is considerable, and somewhat less for paraldehyde and acetonitrile. Acetic acid causes association to double molecules, which become partially dissociated with rise of temperature.

The electrolysis of solutions of lithium chloride in various solvents, such as water, alcohols, glycerol, and phenol, has been investigated by Patten and Mott.The latent heat of fusion of lithium chloride per gram is 0.086 Cal.

The heat of formation of dilute aqueous solutions is given by the equation

LiOH,Aq. +HCl,Aq. =LiCl, Aq. + 13.85 Cal.

Since the heat of solution of hydrochloric acid is 39.3 Cal., and that of lithium in water is given by the equation

[Li]+Aq.=LiOH,Aq. + (H)+53.2 Cal.,

the heat of formation of lithium chloride in dilute solution is given by the equation

[Li]+Cl+Aq.=LiCl,Aq. +106.35 Cal. Since the heat of solution of the anhydrous salt is 8.44 Cal., the heat of formation of lithium chloride from its elements is expressed by the equation

[Li]+(Cl)=[LiCl]+97.9 Cal.

The heat of solution in ethyl alcohol is 11.74 Cal., in methyl alcohol 10.9 Cal. The formation of compounds with alcohols has been investigated. At 25° C. 100 grams of ethyl alcohol dissolve 25.83 grams of the salt.

Lithium chloride forms double salts with the chlorides of other metals, such as copper, manganese, iron, cobalt, nickel, and uranium. With sodium chloride it forms a series of mixed crystals, but not with potassium chloride.

Lithium subchloride, Li₂Cl. - According to Guntz, lithium chloride is converted by lithium into a hard, greyish substance of the formula Li₂Cl. It decomposes water readily:

2Li₂Cl+2H₂O =2LiCl+2LiOH+H₂.