CHAPTER XLIII.

THE COMPOUNDS OF LITHIUM.

FIVE lithium salts are recognized in the Pharmacopoeia together with one effervescent preparation of a salt. A peculiarity of all lithium salts, by which they can readily be distinguished from other alkali salts, is their complete solubility in a mixture of equal volumes of alcohol and ether, after conversion into the chloride. The following is a list of the official lithium preparations:

Lithium Benzoate. LiC,H,O, or CH,COOLI.-This salt is most conveniently prepared from the carbonate, by suspending the same in hot water and adding benzoic acid as long as effervescence continues; the filtrate is evaporated on a water-bath to dryness, with constant stirring, or may be concentrated and set aside to crystallize. To make 100 parts of the salt will require 29 parts of lithium carbonate and 95.3 parts of benzoic acid, the reaction being as follows: 2HC,H ̧O2+ Li¿CO,= 2LiC,H ̧O2+ CO2+ H2O.

The salt is permanent in the air and very soluble in water, but less so in alcohol. The Pharmacopoeia requires 98.5 per cent. purity, which is determined gravimetrically by converting the salt into sulphate, and weighing as such, after ignition. Each Gm. of lithium benzoate will yield 0.43 Gm. of sulphate, and in the official test 0.5 Gm. is required to yield not less than 0.210 nor more than 0.216 Gm., the ammonium benzoate formed being volatilized, whereas the lithium sulphate remains after ignition as a non-volatile residue. The theoretical yield, if the salt be 98.5 per cent. pure, in the official test would be 0.212+ Gm.

Lithium Bromide. LiBr.-For the preparation of this salt diluted hydrobromic acid may be neutralized with lithium carbonate, or the latter salt may be agitated in a flask with a hot solution of ferrous bromide. The first method is probably the most desirable. Owing to the very deliquescent character of the salt it is not readily

crystallized, and is preferably obtained in granular powder form by evaporating the solution to dryness on a water-bath."

Lithium bromide contains about 92 per cent. of bromine, a larger proportion than any other salt. It is very soluble in water and alcohol, and also soluble in ether, and must be carefully preserved in well-stoppered bottles.

The salt is likely to be contaminated with lithium chloride (due to chlorine in the bromine), and the Pharmacopoeia requires not less than 97 per cent. of pure lithium bromide. The official test for the limit (1.75 per cent.) of other alkalies depends upon the solubility of lithium chloride in the amyl alcohol, in which other alkali chlorides are insoluble. The degree of purity is determined volumetrically by means of AgNO, solution; 0.20 Gm. of the dried salt must require not less than 22.5 Cc. nor more than 23.9 Cc. of the silver solution for complete precipitation, potassium chromate being used as indicator. Each Cc. of the silver solution corresponding to 0.008634 Gm. of lithium bromide, 0.2 Gm. of absolutely pure LiBr, would require 23.16+Cc. The presence of other alkali bromides would cause a lesser quantity of the silver solution to suffice. The higher pharmacopoeial limit, 23.9 Cc., is intended to limit the amount of lithium chloride present, and as some chloride is presumably present in all lithium bromide its presence will counteract the effect of other alkali bromides, and thus the titration may show a pure salt when in reality both impurities are present.

Lithium Carbonate. Li,CO,.-The carbonate, the parent salt of the other lithium compounds, is obtained from the mineral lepidolite, a mixture of silicates and fluorides of potassium, sodium, aluminum, and lithium. By digestion with sulphuric acid impure lithium sulphate is obtained, which is freed from the other salts by crystallization, treatment with milk of lime, etc. The final solution of alkali hydroxides is mixed with ammonium carbonate, whereby the lithium carbonate is precipitated; or the mixed alkali hydroxides may be converted into chlorides, and the solution then treated with ammonium carbonate. For the purpose of purification lithium carbonate may be suspended in water and treated with carbon dioxide, when an acid carbonate, LiHCO, will be formed and enter into solution, upon heating which pure lithium carbonate will be precipitated.

Lithium carbonate is the least soluble of all alkali carbonates, and is, moreover, only a little more than half as soluble in boiling water as in cold water. It occurs in commerce as a light, odorless powder.

The Pharmacopoeia demands that if 0.5 Gm. of the salt be dissolved in 20 Cc. of normal acid, not more than 6.6 Cc. of normal alkali shall be required to neutralize the excess of acid, indicating at least 98.5 per cent. of pure Li,CO,. As each Cc. of normal acid corresponds to 0.036755 Gm. of the pure salt, 0.4925 (98.5 per cent. of 0.5) Gm. will require 13.4 Cc. of the acid, for 0.4925 ÷ 0.036755 = 13.4.

Lithium Citrate. Li,CH,O,+4H2O or C,H,OH(COOL), + 4H,0.—This salt can be prepared by adding lithiuni carbonate to a solution of citric acid until the latter is neutralized, then concentrating the solution and allowing it to crystallize. As shown by the equation 2(H,CH,O,+H2O) + 3Li,CO2+3H,O=2(Li,C,H ̧Ó,+ 4H2O)+ 3CO2, 2 molecules or 417 Gm. of citric acid require 3 molecules or 220.53 Gm. of lithium carbonate, the yield of crystallized lithium citrate being about 560 Gm. If the solution be evaporated to dryness and the residue heated to 140° C. (284° F.) an anhydrous salt will be obtained identical with that formerly recognized in the U. S. P.

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The Pharmacopoeia requires 98.5 per cent. purity for lithium citrate, which is determined gravimetrically, as in the case of the benzoate, except that ammonium sulphate is not used, the citrate being ignited and treated with a little nitric and sulphuric acids to convert it into sulphate. The equations 2(Li,CH,O,+ 4H,O) + O18=3Li2CO2+ 9CO2+ 13H2O and 3Li2CO2+ 3H2SO, =3Li2SO, +3CO2+ 3H2O show that 2 molecules or 560.16 Gm. of crystallized lithium citrate will yield 3 molecules or 327.93 Gm. of lithium sulphate, and hence 1 Gm. of the former will yield 0.5854 Gm. of the latter. In the official test 0.5 Gm. of the anhydrous salt is required to yield not less than 0.387 nor more than 0.394 Gm. of sulphate. Lithium citrate contains about 25.5 per cent. of water of crystallization, and as the salt is deliquescent in moist air, the Pharmacopoeia directs that the assay shall be made with anhydrous salt; if absolutely pure, the 0.5 Gm. of citrate will yield 0.3933+ Gm. of sulphate; and if 98.5 per cent. pure, the yield will be 0.3875+ Gm. Any yield of sulphate residue greater than the highest theoretical will therefore indicate the presence of other alkalies or impurities.

Both the anhydrous salt in powder-form and the crystallized salt occur in commerce.

Investigation has shown that the commercial lithium citrate offered in this country is by no means uniform in composition, varying from an anhydrous salt to one containing one or more molecules of water; moreover, according to L. F. Kebler, the anhydrous salt is more or less deliquescent, but becomes non-deliquescent after a certain amount of moisture has been absorbed.

Effervescent Lithium Citrate.-This preparation contains about 5 per cent. of crystallized lithium citrate, and is made by the general process directed in the Pharmacopoeia for the manufacture of all granular effervescent salts. It has already been considered in the Chapter on Granular Effervescent Salts (see page 410).

Lithium Salicylate. LIC,H,O, or CH,(OH)COOLI.-This salt may be prepared by heating a mixture of 44 parts of salicylic acid, 12 parts of lithium carbonate, and 100 parts of water until effer

vescence ceases; it is then filtered and the solution evaporated to dryness. As in the case of sodium salicylate, a slight excess of acid is necessary to avoid discoloration of the finished product, and contact with metal must be carefully avoided.

The Pharmacopoeia requires for lithium salicylate 98.5 per cent. purity, to be determined gravimetrically exactly as in the case of lithium benzoate. Each Gm. of lithium salicylate, if absolutely pure, will yield 0.382 Gm. of sulphate. In the official test 0.5 Gm. of the salt is required to yield not less than 0.188 nor more than 0.192 Gm. of sulphate; the theoretical yield, if the salt be 98.5 per cent. pure, would be 0.188 + Gm.

CHAPTER XLIV.

THE COMPOUNDS OF AMMONIUM.

ALTHOUGH, thus far, all efforts to isolate the basylous radical of ammonium salts have failed, the existence of the hypothetical body NH, must be assumed, as, without it, it would be impossible to explain the formation and composition of a large and important class of compounds in accordance with accepted modern views regarding the replacement of hydrogen in acids. The decomposition of sodium amalgam by means of ammonium chloride, resulting in the production of sodium chloride and a new spongy amalgam having a metallic lustre, points strongly to the metallic character of the radical called ammonium. The indirect source of all ammonium salts is the gaseous body ammonia, NH,, which may be looked upon as ammonium hydroxide minus water, NH ̧OÍ — H2O= NH,; a characteristic feature of these salts is their complete volatilization upon application of heat.

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The Pharmacopoeia recognizes 7 salts of ammonium, 4 preparations of the salts, and 3 solutions of the hydroxide, as follows:

Official English Name.
Ammonium Benzoate,

Ammonium Bromide,

Ammonium Carbonate,

Ammonium Chloride,

Ammonium Iodide,

Ammonium Salicylate,

Ammonium Valerate,
Ammonia Water,

Stronger Ammonia Water,

Liniment of Ammonia,

Solution of Ammonium Acetate,
Spirit of Ammonia,

Aromatic Spirit of Ammonia,
Troches of Ammonium Chloride,

Official Latin Name.

Ammonii Benzoas.
Ammonii Bromidum.

Ammonii Carbonas.

Ammonii Chloridum.

Ammonii Iodidum.

Ammonii Salicylas.
Ammonii Valeras.
Aqua Ammoniæ.

Aqua Ammoniæ Fortior.
Linimentum Ammoniæ.
Liquor Ammonii Acetatis.
Spiritus Ammoniæ.

Spiritus Ammonia Aromaticus.
Trochisci Ammonii Chloridi.

Ammonium Benzoate. NH CHO2 or CH COONH-When benzoic acid is added to diluted ammonia water, the acid is neutralized and ammonium benzoate is formed, which, remaining in solution, may be obtained in colorless crystals, if the liquid be concentrated by aid of a moderate heat and set aside. As ammonium salts are readily decomposed by heat, the liquid should be kept alkaline by the occasional addition of ammonia water during evaporation. To prepare 100 Gm. of the salt requires 87.75 Gm. of benzoic acid and 123 Gm. of the official ammonia water.