salt and a solution of 50 Gm. of the latter, simultaneously, into a large volume of water, with active stirring, when the following reaction occurs: HgCl2 + 2KI HgI, 2KCl. The official formula employs the two salts very nearly in the proportion indicated in the foregoing equation, which are 4 and 4.9+, respectively; an excess of either salt must be avoided, since loss by formation of a soluble compound would result, an excess of potassium iodide producing potassium mercuric iodide (HgI2 + 2Kİ) and an excess of mercuric chloride causing the formation of mercuric iodochloride (HgI, + 2HgCl, or Hg,I,Cl1).

Mercuric iodide is dimorphous, occurring crystallized both in the form of scarlet-red quadratic octahedra and yellow rhombic prisms, but the Pharmacopoeia recognizes the salt only in the form of an amorphous scarlet-red powder, which is obtained by the official method of preparation. When exposed to light, mercuric iodide gradually becomes paler in color, and should therefore be preserved in dark bottles. It is soluble in solutions of metallic iodides and sodium thiosulphate, as well as alcohol, olive oil, castor oil, chloroform, glycerin, and glacial acetic acid, forming colorless solutions in each case.

Yellow Mercuric Oxide. HgO.-The official formula for the preparation of this compound directs that a strong solution of 100 Gm. of mercuric chloride be poured slowly, with constant stirring, into a dilute solution of 40 Gm. of 90 per cent. sodium hydroxide; amorphous mercuric oxide is precipitated, while sodium chloride enters into solution. The mixture is allowed to stand at a moderate temperature for an hour, to facilitate complete decomposition, after which the liquid is decanted and the precipitate repeatedly washed until free from alkali, drained, and dried on paper, in a dark place, at a temperature of 30° C. (86° F.).

Mercuric salts do not form hydroxides when added to alkali hydroxides, but mercuric oxide is precipitated instead, as shown by the equation HgCl, + 2NaOH = HgO + 2NaCl + H2O. HgO+2NaCl It is important that the alkali be used in excess, otherwise a dark-colored oxychloride will be formed; hence the mercuric chloride solution is poured into the alkali solution in the official process. From the above equation it will be seen that 1 molecule (or 268.86 parts) of mercuric chloride requires 2 molecules (or 79.52 parts) of sodium hydroxide for complete precipitation; hence 100 Gm. HgCl, will require 29.6 Gm. NaOH; official sodium hydroxide containing 90 per cent. of NaOH, the necessary excess of alkali is assured in the formula of the Pharmacopoeia, as 90 per cent. of 40 Gm. is 36 Gm. It is essential that the sodium hydroxide used be free from carbonate, otherwise mercuric carbonate will be formed. Potassium hydroxide may be used in place of sodium hydroxide, but ammonia is inadmissible, owing to the formation of ammoniated mercury. In order to insure a bright orange-yellow product, heat and light must be excluded during pre

cipitation and drying; unless protected from light, the color of the oxide gradually darkens on keeping, and if exposed to direct sunlight decomposition rapidly occurs.

Yellow mercuric oxide, being in a state of very fine division, is more active and more sensitive than the red oxide; it is chemically identical with the latter, but differs from it in the molecular arrangement of its particles, being devoid of all crystalline structure. When digested with a solution of oxalic acid, yellow mercuric oxide forms white mercuric oxalate, while the red oxide remains unaffected.

pre

Red Mercuric Oxide. Hg0.-Although the name "red cipitate" is commonly applied to this compound, it is never obtained by precipitation, but always by calcination. As a rule, mercuric nitrate is triturated with metallic mercury until the latter is extinguished; the mixture is then heated in a porcelain dish until yellowish or reddish vapors cease to be evolved and mercuric oxide remains. The metallic mercury is oxidized at the expense of the nitric acid expelled from the mercuric nitrate, and the process may be illustrated by the following equation : 2Hg(NO3)2 + Hg2 = 4HgÖ + 4NO2.

Red mercuric oxide occurs as a crystalline powder or in crystalline scales of an orange-red color, and by trituration with alcohol is gradually converted into a yellowish-red powder. When exposed to light, it darkens in color, but more slowly than the yellow oxide, and, unlike the latter, it is not affected by hot solution of oxalic acid.

Solution of Mercuric Nitrate.-An acid liquid containing about 60 per cent. of mercuric nitrate and about 11 per cent. of free nitric acid. This, the only fluid preparation of mercury officially recognized, is made by solution of 40 Gm. of mercuric oxide in a mixture of 45 Gm. of nitric acid and 15 Gm. of water. According to the equation 3HgO + 8HNO,=3Hg(NO3)2 + 2NO + 4H2O, 643.14 parts of mercuric oxide require 500.56 parts of absolute nitric acid to form 964.92 parts of mercuric nitrate; hence 40 Gm. will require 31.13 Gm. of absolute, or 45.78 Gm. of official, nitric acid and will yield 60.32 Gm. of the salt. Moderate dilution of the acid with water is advantageous, facilitating the solution of the newly formed salt.

This very corrosive preparation, rarely used, and then only for external application, requires great care in handling. It is also known by the name acid nitrate of mercury, and is the densest solution of the Pharmacopoeia, having a specific gravity of 2.086 at 25° C. (77° F.).

Among the non-official compounds of mercury of interest to the pharmacist, the following may be mentioned:

Mercurous Tannate. This compound is prepared by triturating freshly prepared and finely powdered mercurous nitrate with a mixture of tannin and water until a homogeneous smooth mass is obtained. The mass is mixed with a large volume of water, and the green precipitate is washed with water until no trace of nitric acid remains, after which it is dried on porous tiles at a temperature not exceeding 40° C. (104° F.).

Mercuric Carbolate or Phenate. Of the two preparations occurring under this name, the so-called normal mercuric phenate, or mercuric diphenate, Hg(C,H,O), should be dispensed, being a stable preparation. It is obtained by mixing, with constant stirring, an alcoholic solution of mercuric chloride with an alcoholic solution of carbolic acid and potassium hydroxide, draining the yellowishcolored precipitate, washing it with hot water acidulated with acetic acid, and recrystallizing from hot alcohol.

Mercuric Salicylate. HgOC,H,0, or CH,OCOOHg.-This salt may be prepared by adding salicylic acid to freshly precipitated mercuric oxide rubbed into a smooth paste with water and heating the mixture on a water-bath until a snow-white mass remains, free from a yellow tint, which is then washed with warm water to remove excess of acid, drained and dried. The resulting amorphous product constitutes secondary or basic mercuric salicylate, which is the salt generally employed. Normal mercuric salicylate, Hg(C,H,O3)2 or (C.H(OH)COO),Hg, can be obtained by precipitating a solution of mercuric chloride with sodium salicylate in the cold; the resulting product is readily decomposed by heat.

Mercuric Sulphate. HgSO-This salt, which has been mentioned in connection with mercurous and mercuric chloride, may be prepared either by the process mentioned under the latter salt or by heating mercury with sulphuric acid and evaporating the mixture to dryness, when a crystalline product will be obtained; water and sulphur dioxide are eliminated during the operation.

CHAPTER LI.

THE COMPOUNDS OF ANTIMONY, ARSENIC, AND BISMUTH.

WHILE, at one time, the preparations of antimony formed an important part of the physician's armamentarium, they are but rarely prescribed at the present time; those of arsenic and bismuth, however, are still looked upon as valuable remedial agents. The Pharmacopoeia recognizes 1 chemical compound and 1 pharmaceutical preparation of antimony, 2 compounds of arsenic, besides 4 arsenical solutions and 6 compounds of bismuth, as shown by the following list:

THE COMPOUNDS OF ANTIMONY.

Antimony and Potassium Tartrate. 2K(SbO)¤ ̧¤ ̧О + H20. -This salt, which has been known for over two hundred and fifty years, is prepared by boiling a mixture of acid potassium tartrate and antimonous oxide with water for some time, filtering the liquid, concentrating by evaporation, and crystallizing. The British Pharmacopoeia directs that a paste be made of the antimonous oxide, cream of tartar, and a small quantity of water, which is set aside. for twenty-four hours to allow combination to take place, after which more water is added and the mixture boiled for fifteen minutes, to bring all the newly formed double tartrate into solution.

If pure materials be used, the full theoretical yield is generally obtained; but if the antimonous oxide be contaminated with oxychloride, some of the salt will be lost by refusing to crystallize in the acid liquid. The following equation, Sb,O,+ 2KHC,H,O = 2K (SBO)C,H,O+H2O, explains the formation of antimony and

potassium tartrate, the univalent group SbO, known as antimonyl, replacing the hydrogen in the acid potassium tartrate, water being formed at the same time.

The synonyms tartar emetic and tartrated antimony are largely used for this compound, the former being the name generally employed in commerce. The salt is recognized in the British Pharmacopoeia as antimonium tartaratum, and in the German Pharmacopoeia as tartarus stibiatus. It is generally sold in powder form, obtained by trituration of the crystals. Aqueous solutions of tartar emetic gradually develop fungi, and on that account cannot be kept on hand for any length of time, nor can they be mixed with strongly alcoholic liquids without precipitation, as the salt is totally insoluble in alcohol.

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The Pharmacopoeia requires almost absolute purity (99.5 per cent.) for tartar emetic, the valuation being made with iodine solution in the presence of sodium bicarbonate and starch solution. The iodine, acting as an oxidizing agent, converts the antimonyl into meta-antimonic acid, hydriodic acid and sodio-potassium tartrate being also formed; the object of adding sodium bicarbonate is to neutralize the two newly formed acids, thereby preventing decomposition of the hydriodic acid by the meta-antimonic acid, which would liberate iodine and thus vitiate the end-reaction. The official directions to begin titration immediately after addition of the sodium bicarbonate solution are intended to prevent the separation of antimonous oxide, caused by action of the alkali bicarbonate on the antimony and potassium tartrate, a reaction known to occur if the two salts are kept together in solution for some time. The equation (2K(SbO)CH ̧O + H2O) + I + 8NaHCO1 = 2NaSbO, + 4ÑaI + 2KNaC12H ̧Ó + 8CO2+ 5H2O shows that each molecule (or 659.8 parts) of crystallized tartar emetic requires 4 atoms (or 503.6 parts) of iodine for complete oxidation of the antimony present; hence 0.33 Gm. at 99.5 per cent. or 0.32835 Gm. will require 0.25060+ Gm. of iodine or 19.9 Cc. of its tenth-normal solution, for 659.8:503.6 :: 0.32835: x (x = 0.25060), and 0.25060 0.01259 19.9.

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The following compounds of antimony are no longer recognized in the U. S. Pharmacopoeia, but are official in the British Pharmacopoeia, and therefore deserving of consideration: antimony oxide, purified antimony sulphide, and sulphurated antimony.

Antimony Oxide. Antimonous Oxide. Antimony Trioxide. SbO-This compound is obtained by first preparing a solution of antimony trichloride, SbCl,, from antimonous sulphide and hydrochloric acid, pouring this into water, whereby antimony oxychloride, 2SbCl,+5Sb,O, (known as powder of Algaroth), is precipitated, which is then repeatedly washed with water and mixed with a solution of sodium carbonate, converting the oxychloride into pure