Methyl

METHYL, a chemical term which until lately was used in two radically different senses, namely, as designating either the atom-group CH 3 , which in numberless chemical formulae figures as a “radical” (compare Chemistry, vol. V. p. 552), or a gaseous substance of the same composition, which, however, nowadays is generally called “dimethyl,” to distinguish it from the radical. A gas of the composition and the specific gravity (C 2 H 6 ÷ H 2 = 15) corresponding to C 2 H 6 can be produced in two principal ways,—first, by the decomposition of zinc-ethyl by water (Frankland)—

Zn(C 2 H 6 ) 2 + 2OH . H = Zn(OH) 2 + C 2 H 5 H; and, secondly, by the electrolysis of acetate of potash solution (Kolbe), we have virtually

2CH 3 . COOH = (CH 3 ) 2 + 2∞ 2 I +H 2 . +pole. I —pole.

These two gases used to be distinguished as two different substances,—Frankland’s being looked upon as hydride of ethyl, C 2 H 5 . H, Kolbe’s as “real methyl” (CH 3 )(CH 3 ), until Schorlemmer proved their identity by showing that both, when treated with chlorine, yield the same identical chloride of ethyl, C 2 H 5 . Cl. This confirmed the now generally adopted notion that the radical ethyl itself is nothing but methylo-methyl, H 3 C—CH 2 *, so that the filling up of the gap* by an H must necessarily produce “hydride of ethyl” and “dimethyl” in one. The “true methyl” which chemists used to dream of, and which, when treated with chlorine, would yield two CH 3 CΓs analogous to HH + C1C1 = HC1 + HC1, does not, and according to our present knowledge cannot, exist. A quasi apology for it is “marsh gas,” CH 4 , the principal component of the gas mixture which bubbles up from any marshy pond when its mud is stirred up with a stick. It is always produced when vegetable matter decays in the presence of water, and in the relative or absolute absence of air. What everybody knows as “fire-damp” is nothing but a (necessarily explosive) mixture of air with impure marsh gas, produced in the constantly progressing metamorphosis of the coal deposits; in certain districts streams of marsh gas are issuing forth from cracks in the earth; the “holy fire” of Baku is such a marsh-gas spring, which, having once caught fire by accident, continues burning to this day. Perfectly pure marsh gas can only be obtained from zincmethyl, Zn(CH 3 ) 2 , by its decomposition with water (vide supra) ; a nearly pure preparation is procurable by heating a mixture of acetate of potash or soda and caustic alkali to dull redness :—

CH 3 . COONa + NaOH = Na a CO s + CH 3 H. Acetate. Carbonate.

Marsh gas can be prepared synthetically by the action of bisulphide of carbon vapour and sulphuretted hydrogen (both producible from their elements) on red-hot copper, CS 2 + 2H 2 S + 8Cu = 4Cu 2 S + CH 4 (Berthelot). A mixture of marsh gas and chlorine, when exposed to direct sunlight, explodes with formation of hydrochloric acid and charcoal. In diffuse daylight only part of the hydrogen is eliminated and “replaced” by its equivalent in chlorine, which in general leads to the formation of four bodies: CH 3 C1 = CH. + Cl 2 - HC1, chloride of methyl; CH 2 C1 2 , chloride of methylene; CHC1 3 , chloroform; CC1 4 , tetrachloride of carbon. Of these several chloromethanes, as they are called, the first here interests us more than any of the rest, because from it any other methyl compound can be produced by the substitution of the proper kind of radical for the Cl of the CH 3 C1. Thus, for instance, we can convert it into methyl-alcohol by treating the chloride with aqueous caustic potash at 100° C. (Berthelot). This is a most important synthesis, because it is this methylalcohol that, in practice, always serves as the starting point in the preparation of other methyl compounds.

Methyl-Alcohol.— This substance, in ordinary practice, is never made synthetically, but simply extracted from wood-spirit, a commercial substance which is produced industrially in the dry distillation of wood. The woodspirit is contained in the aqueous portion of the tar produced in this operation, along with acetic acid. To recover both, the tar-water is neutralized with lime and distilled, when the acetate remains, while the spirit distils over, along with a deal of water, which, however, is easily removed, as far as necessary, by redistillation and rejection of the less volatile parts. The “crude” wood-spirit, as thus obtained, is not unlike in its general properties to ordinary spirit of wine, from which, however, it is easily distinguished by its abominable smell. The ordinary commercial article, besides a variable percentage of water, contains from 35 to 80 per cent, of methyl-alcohol; the rest consists chiefly of acetone, but besides includes dimethyl-acetal, C 2 H 4 (OCH 3 ) 2 , acetate of methyl, and numerous other minor components. In Great Britain large quantities of wood-spirit are used for the making of methylated spirit, a mixture of ordinary spirit of wine with one-ninth of its volume of wood-spirit, which is allowed to be sold duty free for the preparation of varnishes, and for other industrial purposes. In former times, here as elsewhere, wood-spirit itself used to be employed as a cheap substitute for spiritus vini; but this is no longer so, since the aniline-colour industry has created a large demand for pure methyl-alcohol. Hence in some Continental works the wood-spirit, instead of being sent out as such, is being worked up for its components, by the following sequence of operations:—(1) dehydration by lime; (2) heating, under an inverted condenser, with caustic soda, to convert the acetate into hydrate of methyl; (3) destruction of the bad smells by mild oxidation; (4) distillation in a kind of Coffey’s still, whereby it is split up into approximately pure alcohol, acetone, and “tails.”

The new industry led to the invention of the following technical methods for the determination, in a given spirit, of the percentages of real methyl-alcohol and of acetone.

The alcohol is determined by saturating 5 c.c. of the spirit with hydriodic acid (volatilization of alcohol and iodide of methyl being avoided by means of a cold-water bath and an inverted condenser), and the product poured into water. Iodide of methyl separates out as a heavy oil, which is measured as it is. According to direct trials 5 c.c. of pure methyl-alcohol yields 7’45 c.c. of crude iodide (Krell, Krämer and Grodzky).

For the determination of the acetone the following reagents are required (Krämer) (1) a solution of iodine, prepared by dissolving I 2 = 254 grammes of iodine, by means of (say) 500 grammes of iodide of potassium, in water, and diluting to 1 litre; (2) a solution of caustic soda containing twice (NaOH) grammes per litre; (3) alcohol-free ether. Ten c.c. of the soda are placed in a graduated cylinder and mixed intimately, first with 1 c.c. of the spirit, then with 5 c.c. of the iodine solution. Iodoform separates out (if acetone is present) in minute yellow crystal plates; this product is “shaken aut” by means of 10 c.c. of ether, and determined by evaporating an aliquot part of the ethereal layer in a fared watch-glass to dryness and weighing the residue. C 3 H ft O yields CHI 3 ; hence 1 part of iodoform indicates 0 ‘28 parts of acetone.

The formula of methyl-alcohol and its true chemical character were correctly ascertained by Dumas and Péligot as early as 1834; yet pure methyl-alcohol may be said to have been an unknown substance until 1852, when Wöhler taught us to prepare it, by first extracting the CH 3 of the CH 3 OH in the wood-spirit as oxalate of methyl, and then decomposing the (purified) oxalate with water.

The most convenient raw material to use nowadays is the commercial “pure” alcohol; if wood-spirit is employed it had better first be purified by distillation over caustic soda {vide supra). The formation of the oxalate then is best effected (according to Alexander Watt) as follows: —500 grammes of oxalic acid crystals are mixed with 200 c.c. of oil of vitriol; then 500 c.c. of the spirit are added, the whole kept for a time at 80° C., and then allowed to stand cold for twenty-four hours.

The large crop of oxalate crystals—partly (CH 3 ) 2 C 2 O 4 , partly CH 3 . H . C 2 O 4 —is separated from the liquor by pressure and subsequent drying over vitriol, and then decomposed by distillation with water.

The aqueous alcohol thus obtained is dehydrated by the well-known methods used in the preparation of ordinary absolute alcohol.

According to Krämer, a purer preparation than Wohler’s is obtained by extracting the methyl as formiate instead of as oxalate, which is easily effected by digesting the wood-spirit with a formic acid ofl∙22 specific gravity, and purifying the formic ether by fractional distillation. This ether boils at 32°, the oxalate at 16Γ C., hence a proper combination of the two methods should be infinitely superior to either. What now follows must, in general, be understood to refer to Wöhler’s preparation.

Pure methyl-alcohol is a colourless liquid similar in its general properties, in its behaviour to other chemically inert liquids, and in its action as a solvent to ordinarj absolute alcohol, from which, however, it differs by the entire absence from it of all spirituous odour. A preparation which smells of wood-spirit may be condemned at once as impure. According to H. Kopp, its specific gravity is 0∙8142 at 0° C. and 0'7997 at 16° '4. If the volume at t° be V, then (from 0° to 6Γ)

V = l+ O001134ι! + l∙364 ×10- 6 Z 2 + 8∙741 ×10-⅜ 3 .

The boiling point is 64°‘6 to 65°'2. The tension-curve was determined by Régnault and by Landolt; but the results of the two observers do not agree except (approximately) at P = 760 mm. Methyl-alcohol has quite a characteristic tendency to “bump” badly on distillation, which, however, can be prevented by addition of a small fragment of tinsodium, which produces a feeble but sufficient current of hydrogen. Its specific heat is *6713; latent heat of vapour, 26'4; combustion heat, 5307 per unit weight (Favre and Silbermann). The refractive index for the D (sodium) ray is 1'3379 = fc '0013 for 10° =f 5 o C. (Dale and Gladstone).

Methyl-alcohol mixes with water in all proportions with contraction.

Since Wöhler’s discovery a table for the specific gravities of aqueous methyl-alcohols has been constructed experimentally by A. Dupre; but unfortunately his alcohol boiled at 58° - 7, and consequently must have been something different from what generally goes by this name.

In its chemical reactions methyl-alcohol, CH 3 .OH, is very similar to ordinary (ethyl) alcohol, C 2 H 5 . OH, and consequently, in the same sense as the latter, analogous to water, H. OH. Thus, for instance, metallic sodium and potassium dissolve in either alcohol with evolution of hydrogen and formation of ethylates or methylates of the alkali metals. Example—

CH 3 OH + Na = CH 3 .0Na + ⅜H 2 .

The two methylates crystallize from the solution with crystal-alcohol, which can be driven off in an atmosphere of hydrogen by heat, without decomposition of the salts themselves. Water at once decomposes them into caustic alkali and alcohol, CH 3 . ONa + H. OH = NaOH + CH 3 OH. Yet the reverse reaction takes place when the alcohol is treated with a large excess of caustic soda.

The action of acids on methyl-alcohol is in general quite analogous to that on, for instance, caustic soda, with this important difference, however, that what in the case of NaHO goes on so readily in aqueous solutions with CH 3 . OH succeeds only under circumstances precluding the accumulation of water. In these circumstances we have, for instance,

(1) ClH + OH. CH 3 = H 2 O + Cl. CH 3 ;

(2) (C 2 H,O 2 )H + OH. CH 3 = H 2 O + C 2 H 3 0 2 . CH 3 ; Acetic acid. Acetic ether and so on with all monobasic acids. A dibasic acid XHH may act as (X)H 2 or as (XH). H; thus, for instance,

(3) (C 2 O 4 H)H + OH . CH 3 = H 2 O + C 2 O 4 . HCH 3 ; Oxalic acid. Methyl oxalic acid.

(4) (C 2 O 4 )H 2 + 2OH. CII 3 = 2H 2 O+ C 2 O 4 . (CH 3 ),;

Methyl oxalate. ·

A tribasic acid forms two methyl acids and one neutral ether; we have, for instance,

(5) (From PO 4 H 3 )j PO 4 (CH 3 )H 2 ; PO 4 (CH 3 ) 2 H; PO 4 (CH 3 ) 3 .

It would, however, be a great mistake to suppose that whether, for instance (Ex. 3 and 4), the monomethyl or the dimethyl compound is formed depends on the quantity of methyl-alcohol employed per unit of acid. This depends far more largely on other conditions, as will be illustrated in next paragraph. The methyl-salts of oxygen acids are called esters, in opposition to the chloride, bromide, iodide, sulphide, and oxide, which are set apart as ethers. Broadly speaking, ethers are not, while esters are, readily decomposed by water into their cogeners; but the nitrate CH 3 . NO 3 behaves in this respect like an ether.

Action with Sulphuric Acid.— Methyl-alcohol mixes with oil of vitriol with considerable evolution of heat and (always only partial) conversion of the two ingredients into methylsulphuric acid. Equal volumes of acid and alcohol give a good yield. To prepare pure methyl sulphates, dilute the mixture largely with water, avoiding elevation of temperature (which would regenerate the ingredients), and saturate with carbonate of baryta. Filter off the sulphate of baryta to obtain a solution of the pure methyl sulphate SO 4 . CH 3 . ba (where ba == ⅜Ba = 1 eq.), from which this salt is easily obtained in crystals. From the baryta salt any other methyl sulphate is readily obtained by double decomposition with a solution of the respective sulphate; the acid itself, for instance, by means of sulphuric acid. At higher temperatures the reaction between vitriol and methyl-alcohol results in the formation of methyl-ether, (CH 3 ) 2 O, or of normal sulphate of methyl, (CH 3 ) 2 SO 4 . The ether is a gas condensable into a liquid which, under pressure of one atmosphere, boils at - 21° C.

The gas dissolves in about one thirty-seventh of its volume of water; far more largely in alcohol and in ether; most abundantly in oil of vitriol, which dissolves about six hundred times its volume of methyl-ether gas, thus affording a very handy means for storing up the gas for use. The solution needs only be diluted with its own volume of water to be broken up into its components (Erlenmeyer).

Liquefied oxide of methyl is now being produced on the manufacturing scale, and sold as a powerful refrigerating agent. One part of sulphuric acid is mixed with a little over one part of dehydrated wood-spirit, and the mixture heated to 125° to 128° C. (130° being carefully avoided), when methyl-ether goes off. When the mixture is exhausted, more wood-spirit is added to the residue so as to re-establish the original specific gravity (of 1 - 29), and the heating resumed, which again furnishes a supply of the gas, and so on. This proves that the process is not, as used to be supposed, one of mere dehydration, but a cycle of reactions analogous to those in the ordinary process of etherification, as shown by the equations :—

(1) SO 4 H 2 + CH 3 OH = SO 4 .HCH 3 + H 2 O.

(2) SO 4 . H . CH 3 + H. 0. CH 3 = SO 4 HH + CH 3 .0. CH 3 .

The ester, SO 4 (CH 3 ), though obtainable by distillation of the alcohol with 10 parts of vitriol, is more conveniently prepared from Eure methyl-sulphuric acid by distillation in vacuum at 130°-140°; thus:—2SO 4 CH 3 . H = SO 4 H 2 + SO 4 (CH 3 ) 2 , It is a colourless liquid, smelling like peppermint, specific gravity 1 ’ 327 at 18°; it boils at 187° to 188° C.

Chloride of methyl, CH 3 C1, readily produced by the action of hydrochloric acid gas and hot methyl-alcohol (preferably in the presence of chloride of zinc as an auxiliary dehydrator), is a gas which, under ordinary pressure, condenses into a liquid at - 23° C. The gas, at ordinary temperatures (though very readily soluble in alcohol), is only sparingly absorbed by water, which, however, at 6° unites with it into a solid hydrate. Condensed methyl chloride has become an article of commerce, being largely produced from trimethylamine (vide infra) and used as a powerful frigorifie agent, as well as for the extraction of perfumes from flowers. Regarding nitrite of methyl, NO—O—CH 3 , its interesting isomeride nitromethane, O 2 N—CH 3 , and nitrate of methyl, NO 3 CH 3 , we must refer to the handbooks of organic chemistry.

Iodide of methyl, CH 3 , is obtained by distilling methylalcohol with hydriodic acid, which latter is best produced off-hand by addition to the alcohol of iodine and amorphous phosphorus. It is a colourless liquid of 2 - 269 specific gravity, boiling at 42 o- 5 C., insoluble in water.

Organic Μ ethyl-Esters.— The more volatile ones are in general easily obtained by distillation of the respective acid with methyl-alcohol, or with methyl-alcohol and oil of vitriol (virtually SO 4 . H. CH 3 ); the less volatile ones more conveniently by passing hydrochloric acid gas into a methyl-alcoholic solution of the acid. We have no space for the individual substances; but the salicylate C 7 H 5 O 3 . CH 3 may just be named as being the principal component of the essential oil of Gaultheria procumbens (wintergreen oil).

Methylamines.— The general result of the action of ammonia on an ester is the formation of alcohol and acid amide. Example—

(C 2 H 3 O)- O-CH 3 + HNH 2 = CH 3 . OH + C 2 H 3 O. NH 2 . Acetate of methyl. Acetamide.

With iodide of methyl this reaction is an obvious impossibility; what really takes place (as A. W. Hofmann has shown for this and all analogous cases) is that the iodide unites with the ammonia into the HI compound HI. NH 2 CH 3 of a base NH 2 CH 3 , which can be separated from the acid by distillation -with caustic potash, and when thus liberated presents itself as a gas surprisingly similar (almost to identity) to ammonia. The analogy extends to the action on iodide of methyl, which, in the case of methylamine, NH 2 CH 3 , leads to the formation of dimethylamine, NH . (CH 3 ) 2 ; and from the latter again trimethylamine, N(CH 3 ) 3 , can be prepared by a simple repetition of the operation. These three amines are closely analogous in their chemical character to ammonia, the points of difference becoming the more marked the greater the number of (CH 3 ) , s in the molecule. Trimethylamine, having lost all its ammonia-hydrogen, cannot possibly act upon iodide of methyl like its analogues. What it really does is to unite with the iodide into “iodide of tetramethyl-ammonium,” I. N(CH 3 ) 4 , analogous to iodide of ammonium, INH 4 , we should say, if it were not the reverse, because the organic iodide (unlike its prototype, which is an ammonium compound only in theory), when treated with moist oxide of silver (virtually with AgOH), really does yield a solution of a true analogue of caustic potash in the shape of hydroxide of tetramethyl-ammonium, N(CH 3 ) 4 . OH.

In regard to the actual preparation of these several bodies, which is not so simple as might appear from our exposition of their mutual relations, we must refer to the handbooks of organic chemistry. But we must not omit to state that trimethylamine, which only the other day was never seen outside a chemical museum, is now being manufactured on a large scale, and promises to play an important part in industrial chemistry. The waste liquors obtained in the distillation of alcohol from fermented beetroot molasses serve as a raw material for its preparation. These liquors, when evaporated to dryness and subjected to dry distillation, yield, besides tar and gases, an aqueous liquid containing large quantities of ammonia, acetonitrile, methyl-alcohol, and trimethylamine. This liquor is neutralized with sulphuric acid, and distilled, when the nitrile and the methyl-alcohol distil over, to be recovered by proper methods. From the mixed solution of the sulphates of ammonia and trimethylamine the former is separated out as far as possible by crystallization; the mother-liquor is distilled with lime; the volatile bases are absorbed in hydrochloric acid; the hydrochloric solution is evaporated; and the sal-ammoniac which comes out at first is, as far as possible, fished out. The last mother-liquor is evaporated to dryness, and in this form represents commercial trimethylamine hydrochlorate. It is this product which serves for the preparation of methyl chloride (vide supra), the process being founded upon the fact that a concentrated solution of the salt, when heated, breaks up 3HC1. N(CH 3 ) 3 into 2N(CH 3 ) 3 of free trimethylamine 4- NH 2 . CH 3 HC1 of hydrochlorate of monomethylamine and 2CH 3 C1 of methyl chloride.

These processes are being carried out industrially by Vincent in France. But this base trimethylamine seems destined to do more than provide us with a new refrigerating agent. The attempt has been made —it would appear, with success—to utilize it for the preparation of pure carbonate of potash from native chloride of potassium, just as ordinary ammonia, in the famous ammonia-soda process, serves for the conversion of common salt into sodaash.

Methyl Cyanides.— There are two distinct bodies which, by composition and by synthesis, are both CH 3 + NC; they are named “acetonitrile” (formerly called simply cyanide of methyl) and isocyanide of methyl or methylcarbamine respectively.

Acetonitrile was discovered by Dumas in 1847. It may be prepared by the distillation of a mixture of methylsulphate and of cyanide of potassium; but is obtained more easily and in a purer state by distilling acetamide with phosphoric anhydride. Acetate of ammonia may be used instead of the amide, but it does not work so well.

CH 3 . CO. O(NH 4 ) CH 3 .CO.(NH 2 ) ch 3 .cn

Acetate of NH 3 Acetamide Nitrile

= A (say). = A-H 2 O. = A-2H 2 O.

It is a colourless liquid of a pungent aromatic odour, with specific gravity - 805 at 0°, and boils at 82° C. When heated with aqueous potash (at the wrong end of a condenser) it breaks up with formation of ammonia and acetate of potash. Whence we conclude that the methyl is combined more directly with the carbon of the cyanogen, thus:

N{C-CH 3 } + 2H 2 O = NH 3 + CH 3 . C00H .

Acetic acid.

This conclusion is supported by the action on the nitrile of nascent hydrogen, which leads to the formation of ethylamine, thus (Men-dius) :—

NC—CH 3 + 4H = H. 2 N-CH 2 CH 3 . Etlιylamine.

In either case we pass from a monocarbon to a dicarbon body, virtually from methyl to ethyl alcohol.

The isocyanide is prepared by heating iodide of methyl with cyanide of silver (CH 3 I; 2NCAg) and ether in a sealed-up tube to 130° to 140°, to produce the crystalline body AgNC + NCCH 3 (and Agi). The double cyanide, when distilled with some water and cyanide of potassium, breaks up into its components,—the NC’Ag forming (NC) 2 AgK; and the cyanide of methyl distils over. It is a colourless liquid, characterized by quite an unbearably irritating and sickening smell. The specific gravity is '756 at 14°, the boiling point 59° C. It combines with hydrochloric acid into a crystalline salt which is readily decomposed by water into methylamine and formic acid. Whence we conclude that in this case the cyanogen is tied to the methyl by its nitrogen; thus :—

C {N—CH 3 } + 2H 2 O = H. C00H + NH a . CH 3 .

Formic acid. Methylamine.

The methyl here remains methyl, being separated by an N from the cyanogen-carbon, which latter passes into formic acid.

We must not close this section without at least referring to the methylphosphines, as being a set of bodies related to PH 3 (phosphine) as the methylamines are to NH 3 (ammonia), and similar to these in their chemical character, in so far as they are bases. The points of difference between the two series are of pretty much the same sense as those between the two prototypes. Thus, for instance, while trimethylamine N(CH 3 ) 3 is a strong base, but inert to oxygen gas, trimethylphosphine is a relatively feeble base, but in contact with air greedily absorbs oxygen with formation of an oxide P(CH 3 ) 3 O, the like of which in the nitrogen series has no existence.

Sulphur Compounds of Methyl.— Substances analogous to methylalcohol and methyl-ether respectively can be obtained by the distillation of methyl sulphate of potassium with strong solutions of the potassium sulphides KHS and K 2 S respectively. The body CH 3 . SH is known as methyl-mercaptane, the other (CH 8 ) 2 S as sulphide of methyl. Both are very volatile stinking liquids. Sulphide of methyl claims a special interest as being the starting point for the preparation of an important class of bodies called trymethyl sulphine compounds. The sulphide (CH 3 ) 2 S readily unites with the iodide CH 3 I into crystals of iodide of"trimethyl sulphine, (CH 3 ) 3 S. I, a substance which is closely analogous in its chemical character to the iodide of tetramethyl-ammonium. Moist oxide of silver, for instance, converts it into a strongly basic hydrate, S(CH 3 ) 3 . OH, which in its avidity for acids almost beats its analogon in the nitrogen family. An investigation of its salts was published by Crum Brown and Blaikie.

Methyl Arsenides.— Arseniferous bases constituted like mono-or di-methylamine (bodies such as AsH 2 CH 3 , analogous to NH 2 . CII 3 ) do not seem to exist. What we do know of are—(1) a trimethylarsine and the iodide and the hydroxide of tetramethylarsonium, —As(CH 3 ) 3 , As(CH 3 ) 4 I, and As(CH 3 ) 4 OH,—bodies discovered by Cahours and Riche; (2) a whole series of monomethylic bodies, As(CH 3 )X 2 (where X = C1, Br, orX 2 =O,S), discovered by Baeyerin 1857; (3) the kakodyle compounds, a series of bodies, As(CH 3 ) 2 . X or As(CH 3 ) 2 . X 3 , which were discovered and investigated by R. Bunsen in 1842. This great investigation marks an epoch in the history of organic chemistry, and our article would not be complete without at least a short summary of its results. Bunsen started in his investigation with a liquid which had been obtained by Cadet as early as 1760, by the dry distillation of equal parts of white arsenic and anhydrous acetate of potash, and which nobody cared to investigate because it emits fumes which have an indescribably sickening smell and an intensity of poisonous action, compared with which that of white arsenic itself appears insignificant. It was reserved for Bunsen to attack this awful substance and force it to give an account of itself. According to Bunsen, Cadet’s liquid is substantially an oxide, (AsC 2 H 6 ) 2 O, which has strongly basic properties, readily exchanging its 0 for Cl 2 , &c. To obtain the pure substance, the liquor is distilled with corrosive sublimate and hydrochloric acid, which in the first instance yields the pure muriate of the base As(CH 3 ) 2 C1, in the form of a liquid volatile above 100° into vapours which take fire spontaneously in air. From this chloride of kakodyle the pure oxide is obtained by distillation with caustic potash. The pure oxide emits no fumes; its specific gravity is 1*462; it boils near 150°. A mixture of its vapour with air detonates at 50° C. From the chloride again, Bunsen obtained the free radical kakodyle, (AsC 2 H β ) 2 , by treatment with metallic zinc in a special apparatus, so constructed that all the several operations involved could be carried out without bringing the contents in contact with air,— a necessary precaution, because kakodyle is a liquid which takes fire in air spontaneously even at ordinary temperatures. Pure kakodyle is a heavy colourless liquid boiling at about 170° C., and freezing at - 6°. When exposed to oxygen or chlorine it suffers destructive combustion; but on slow access of air it is oxidized into its oxide, (AsC 2 H 6 ) 2 O, and kakodylic acid; with chlorine water it unites into the chloride λvhich it came from; it also unites directly with sulphur and other elements; in short, it is exactly to kakodyle compounds what potassium is to potash and potash salts, “a true organic element,” as Bunsen himself put it. This discovery of Bunsen’s was greeted with an enthusiasm which it is difficult in these days to realize. With us now, a radical is intrinsically a fiction; it was different in 1842. By the isolation of kakodyle the “radical” notion suddenly rose from an unproved hypothesis to the rank of a theory based on experiment. Still, however much our theoretical notions may shift, Bunsen’s research will stand as a piece of monumental scientific work.

Kakodylic acid, As. 0. (CH 3 ) 2 . OH, is most conveniently prepared from the oxide by addition of water and oxide of mercury, — H 2 O + 2HgO supplying the H 2 + O 3 required for l(AsC 2 H β ) 2 O. This is a crystalline monobasic acid, soluble in water. Unlike the kakodylides of the As. X ? type, it has no smell, and is no very violent poison. It takes six grains of it to kill a rabbit.

Metallic Methides.— Examples of these are—Sb(CH 3 ) 3 j Sb(CH 3 ) 5 ; Mg(CH 8 ) 2 ; Zn(CH 8 ) 2 ; Pb(CH 3 ) 4 ; A1(CH 3 ) 3 ; Sn(CH 3 ) 4 . To give an idea of the chemical character of this interesting class of bodies we choose zinc-methyl as a representative example, and state briefly the chief points of its chemical history. This body was discovered by Frankland in 1849. It is prepared by boiling iodide of methyl over granulated zinc in a flask connected with an inverted condenser, and so contrived otherwise that the contents are protected against access of moisture and oxygen. Under these circumstances the two ingredients gradually unite into a non-volatile and solid compound IZn . (CH 3 ). When this body is heated with more of iodide of methyl, it undergoes decomposition, with formation of iodide of zinc and of dimethyl gas, I—Zn—CH 3 + CH 3 I = ZnI 2 + (CII 3 ) 2 , which reaction to some extent takes place unavoidably in the preparation of the zinc salt, however great an excess of metal may be taken. What survives needs only to be subjected to dry distillation (in the absence of air) to yield a distillate of zinc-methyl :—

21—Zn—CH 3 = Znl 2 + Zn(CII 3 ) 2 .

Zinc-methyl is a colourless liquid of 1 - 3S6 specific gravity at 10 o- 5, which boils at 46° C.; in contact with air it takes fire. Water decomposes it at once into hydrate of oxide of zinc and marsh gas, Zn(CH 3 ) 2 = Zn(OH) 2 + 2CH 3 H. Of other reactions the following may be named. (1) When digested with sodium, it yields a precipitate of metallic zinc, and a double compound of itself and sodiummethyl. This latter unites readily with carbonic acid into acetate of soda, NaCH 3 + CO 2 =CH 3 —CO—ONa (Wanklyn). (2) With chloride of acetyl it forms acetone, Zn(CH 3 ) 2 + 2CH 3 . CO. Cl = ZnCl 2 + 2CO(CH 3 ) 2 (Freund). (3) Under somewhat different conditions, including the presence of an excess of Zn(CH 3 ) 2 , a compound is produced which with water, yields tertiary butyl-alcohol (Boutle-row):

CO(CH 3 ) 2 + Zn(CH 3 ) 0 =C(CH 3 ) 3 .0. ZnCH 3 = A;

A + 2H. OH = Zn(OH) 2 + CH 4 + C(CH 3 ) 3 -OH.

Tertiary alcohol. ( W. D. )