changed, but in reality are decomposed into cacodylic oxide and haloid, which recombine on cooling.

321. Cacodylic cyanide, As(CH3)2.CN, crystallises in large prisms of diamond lustre, of melting point 37° and boiling point 140°. This extremely poisonous body is obtained by distillation of alkarsin with concentrated hydrocyanic acid or of cacodylic chloride with mercuric cyanide.

322. Dimethyl-arsen trichloride, cacodylic trichloride, As(CH3)2C13, results from the action of chlorine gas upon cacodylic chloride, the latter being previously diluted with carbonic disulphide in order to moderate the violence of the reaction. The trichloride separates partially in crystalline plates. Another method of preparation consists in the action of phosphoric chloride on cacodylic acid, placed under anhydrous ether:

As(CH3)2O.OH + 2PC15 = As(CH3)2Cl3 + HCl + 2POCI3.

It is dissolved by ether or carbonic disulphide, and crystallises on evaporation of these solutions in clear plates. It decomposes at 40°-50° into arsen-monomethyl dichloride and methylic chloride : As(CH3)2Cl3 = As(CH3)Cl2 + CH3Cl.

By water it is readily converted into cacodylic chloro-dihydrate ($ 324).

323. Cacodylic acid, dimethyl arsinic acid:

Cacodylic acid is usually prepared by means of cacodylic oxide and mercuric oxide. For this purpose alkarsin is added to several times its volume of water, and mercuric oxide slowly added with gentle shaking until the odour of alkarsin has completely disappeared:

[As(CH3)2]2O + 2HgO + H2O = 2Hg + 2As(CH3)2.O.OH. The liquid poured off the reduced mercury contains cacodylic acid and some mercuric cacodylate, for whose complete decomposition a small quantity more alkarsin is added. By evaporation of the clear solution cacodylic acid is obtained in large colourless prisms, which melt at 200°, with partial decomposition. It is readily soluble in water, difficultly in alcohol, insoluble in ether. The solution reacts and tastes decidedly acid. By reducing agents it is reconverted into cacodylic oxide. Oxidising agents, even fuming nitric acid, are without action on it.

It reacts on metallic oxides and carbonates, forming crystalline salts, cacodylates, soluble in water. Potassic cacodylate forms concentricly grouped needles, which quickly deliquesce in moist air; argentic cacodylate, As(CH3)2O.OAg, crystallises in delicate colourless needles, which blacken on exposure to light; cacodylic cacodylate has been already mentioned (§ 319).

324. Cacodylic chloro-dihydrate, or cacodylic acid hydrochloride, is obtained from cacodylic trichloride by action of water, or more readily by dissolving cacodylic acid in concentrated hydrochloric acid and

evaporation of the liquid in vacuo. It separates in deliquescent, acid-reacting leafy crystals, of the formula As(CH3)2O2H2Cl. Its formation is expressed by the following equations:

325. Sulphides of Cacodyl.-Two compounds of cacodyl with sulphur are known.

Cacodylic sulphide, [As(CH3)2]2S, corresponds in composition to cacodylic oxide. It is obtained by distillation of cacodylic chloride with baric sulphide :

as a colourless, heavy, oily liquid, which mixes with alcohol and ether. Its odour is penetrating and resembles both alkarsin and mercaptan. The boiling point is above 100°. With hydrochloric acid it gives cacodylic chloride and hydric sulphide.

Cacodylic persulphide, cacodylic sulpho-cacodylate :

corresponding to cacodylic cacodylate, is formed from the preceding by direct addition of sulphur, as also from cacodyl. It crystallises in colourless rhombic tables, which are readily soluble in alcohol, difficultly in water, and insoluble in ether, and which melt at 50°. If an alcoholic solution be mixed with alcoholic plumbic acetate, insoluble plumbic sulpho-cacodylate separates in colourless nacreous scales, whilst the solution contains cacodylic acetate :

=

2[As(CH3)2S.S.As(CH3)2] + Pb(O.C2H3O)2
As(CH3)2S.S

As(CH3)2S.SPb+ 2As(CH3)2.O.C2H2O.

Other salts of sulpho-cacodylic acid have also been prepared, but all attempts to separate the free acid, As(CH3)2S.SH, have so far been unsuccessful.

326. Several of the diethyl-arsen compounds or ethyl-cacodyl derivatives have been prepared. They correspond in method of preparation and properties to the methyl bodies. The starting point is diarsen-tetrethyl, As2(C2H5), or ethyl cacodyl, which results, together

with triethyl arsine, from the action of ethylic iodide upon sodic arsenide, and on fractional distillation of the product passes over last. It is a yellowish, heavy liquid, boiling between 185° and 195°, of garlic odour, and is spontaneously inflammable in air. It unites directly with oxygen, sulphur, and the halogens. By addition of iodine, e.g. diethyl-arsen iodide, As(C2H¿)¿I, is obtained as a yellowish oil insoluble in water.

On allowing a dilute alcoholic solution of ethyl cacodyl to remain for a long time exposed to the air, it is slowly converted into diethyl arsonic acid, As(C2H3)2O.OH. On evaporation it is obtained in strongly acid crystals, which deliquesce in moist air.

Arsen-monomethyl Compounds.

327. Of the monalkyl-arsen derivatives only those of methyl have been obtained in a state of purity and investigated. If cacodylic trichloride be submitted to distillation (§ 322) it evolves methylic chloride gas; and arsen-methyl dichloride, As(CH3)Cl2, condenses in the receiver as a heavy, colourless, strongly refractive liquid, which boils at 133° and is pretty soluble in water. Its vapour attacks the mucous membrane violently. It is also formed by the distillation of cacodylic acid in an atmosphere of hydrochloric acid :

On passing chlorine into arsen-methyl dichloride, mixed with carbonic disulphide and cooled to -10°, there separates

Arsen-methyl tetrachloride, As(CH3)C14, in large crystals, which decompose at 0° into arsenious trichloride and methylic chloride :

328. If arsen-methyl dichloride be mixed with water and sodic carbonate, there is formed

Arsen-methyl oxide, As<CH3, according to the equation :

As(CH3)Cl2 + Na,CO3 = 2NaCl + CO2 + As(CH3)0.

After evaporation of the water it is extracted from the residue by absolute alcohol, and is obtained by evaporation of the filtered liquid in short prisms, of indifferent reaction, little soluble in cold water and of 95° melting point. It is also formed on distilling arsendimethyl chloro-dihydrate, or cacodylic acid hydrochloride :

In the presence of aqueous vapour it volatilises. By the haloid acids and by sulphuretted hydrogen it is converted respectively into the haloid compounds and the sulphides.

Arsen-methyl diiodide, As(CH3)2, crystallises in long brilliant yellow needles, which melt at 20° and distil unaltered at above 200°. Arsen-methyl sulphide, As(CH3)S, forms brilliant leaves or prisms, which melt at 110°.

329. On treating a mixture of arsen-methyl oxide and water with mercuric oxide, mercury separates, and the solution contains the mercuric salt of

ing to methyl phosphinic acid (§ 304), is usually obtained in the free state by addition of the requisite quantity of sulphuric acid to the baric salt. By evaporation of its aqueous solution it is obtained in large spear-shaped laminæ, composed of small dendritic needles of agreeable acid taste. Baric methyl arsinate, As(CH3)O<

Ba, is obtained from the mercuric salt by addition of baric hydrate until all mercuric oxide is precipitated and evaporation of the filtrate. From its dilute aqueous solution alcohol precipitates the same salt with five molecules of water of crystallisation in colourless needles. The silver salt, As(CH3)O.(OAg), is precipitated from solutions of the baric salt in nacreous crystals, which detonate at 100°.

ANTIMONY COMPOUNDS OF THE ALCOHOL RADICALS.

330. Only those antimony compounds corresponding to the tertiary arsines and quaternary arsonium compounds are known. They are in nearly all respects analogous to these bodies.

They are prepared by action of alkylic iodides upon potassic antimonide. This alloy is best prepared by carbonising tartar emetic (potassic antimonylic tartrate) and strongly heating the product in covered vessels.

The reaction between the finely powdered alloy and the alkylic iodide is accompanied with great evolution of heat. The resulting tertiary stibine is then if its boiling point be not too high-distilled off in vessels filled with carbonic anhydride, whilst potassic iodide and excess of antimony remain behind :

SbK3+3CnH2n+1I Sb(CnH2n+1)3 + 3KI.

=

The tertiary stibines oxidise rapidly--often spontaneously inflaming-on exposure to air, forming the oxides Sb(CnH2n+1)30, which have the properties of a diacid basic anhydride, and yield hydric and normal salts with acids.

Similarly to their behaviour with oxygen, the tertiary stibines unite directly with one atom of sulphur or two atoms of halogen, and further unite with the elements of a molecule of an alkylic iodide to quaternary stibonium iodides, Sb(CnH2n+1), I, from which, by action of argentic oxide, the caustic, alkaline monacid bases, Sb(CnH2n+1).OH, can be prepared.

Antimon-methyl Compounds.

331. Trimethyl stibine, or antimon-trimethyl, Sb(CH3)3, is obtained, by heating methylic iodide with potassic stibide, as a heavy, colourless liquid, insoluble in water, little soluble in alcohol, but readily in ether. Exposed to air, it fumes and soon inflames spontaneously. Its oxide, sulphide, and halogen compounds have been prepared, but not thoroughly investigated; they completely resemble those of trimethyl stibine. Trimethyl-stibine diiodide, Sb(CH3)3I2, can be also prepared in beautiful crystals by direct heating of powdered antimony with methylic iodide at 140°:

Sb, +9CH,I=3Sb(CH3)312 + SbI3.

By bringing together trimethyl-stibine iodide and zinc methyl, and subsequent distillation, an oily liquid passes over between 96° and 100°, not spontaneously inflammable antimon-pentamethyl-and is formed according to the equation :

Sb(CH3)312 + Zn(CH3)2 = ZnI2 + Sb(CH3)5.

332. If trimethyl stibine be mixed with methylic iodide, combination occurs without the aid of extraneous heat. A white hard mass of tetramethyl stibonic iodide, Sb(CH3),I, is obtained, which dissolves in hot water, and on cooling separates in beautiful hexagonal tables. This compound is readily soluble in alcohol, difficultly in ether. On boiling the aqueous solution with argentic oxide, argentic iodide separates, and the filtered liquid yields on evaporation in vacuo a white crystalline deliquescent mass of tetramethyl stibonic hydrate, Sb(CH3)4.OH; this is a strong base, has a caustic action like that of potassic hydrate, and is readily soluble in alcohol. On slow heating it can be partially volatilised without decomposition. Its salts are obtained directly by neutralisation with acids, or by decomposition of the iodide with silver salts.

Tetramethyl stibonic chloride, Sb(CH3),Cl, and the bromide, Sb(CH3), Br, crystallise like the iodide in hexagonal tables; the first gives with platinic chloride an orange yellow crystalline precipitate of the formula [Sb(CH3)4C1]2,PtCl4.

The nitrate, Sb(CH3),O.NO2, prepared by double decomposition of the iodide with argentic nitrate, crystallises in readily soluble prisms, like those of potassic nitrate.

The sulphates are prepared from the hydrate and sulphuric acid. The normal sulphate, [Sb(CH3)4]2SO4,5H2O, forms rhombic efflorescent crystals, of neutral reaction; the hydric sulphate, Sb(CH3)4.HSO4, transparent hard tables of strongly acid reaction.

Both carbonates are known and are prepared like those of the alkali metals. The normal carbonate, [Sb(CH3)4]2CO3, is an indistinctly crystalline mass of alkaline reaction; the acid salt, [Sb(CH3),]HCO3, crystallises in star-like groups of needles, which are deliquescent and of alkaline reaction.

Antimon-ethyl Compounds.

333. Triethyl stibine, or antimon-triethyl, Sb(C2H5)3, is obtained by the above-given method as a colourless liquid of sp. gr. 1·324 and 158° boiling point; it fumes in air and easily inflames spontaneously.