the putrefaction of albuminoids; e.g. it occurs largely in rotten cheese. It is obtained synthetically by boiling isobutylic cyanide with alkalies and by oxidation of isoamylic alcohol.

This succeeds best when five parts of potassic dichromate are placed with four parts of water in a retort turned upwards and provided with an inverted condenser, and a mixture of one part of fermentation amylic alcohol and four parts of sulphuric acid then added. The reaction soon starts of itself with lively ebullition. Later it is heated to boiling until no oily streaks of isoamylic aldehyde can be observed in the neck of the retort or the condenser. The retort is then turned downwards, and the valeric acid, together with water, distilled over. The distillate is saturated with sodic hydrate, the oily isoamylic isovalerate which separates removed, the salt solution evaporated to dryness and treated with four-fifths of its weight of sulphuric acid that has previously been diluted with half the quantity of water. The oily valeric acid is then separated, dried with calcic chloride, and purified by distillation.

Isovaleric acid is a thin, colourless oil of unpleasant valerian-like odour. It has sp. gr. 947 at 0°; it boils at 175°. The anhydrous acid, on shaking with water, takes up a molecule of the latter:

(CH3)2CH.CH2.CO.OH + OH2 = (CH3)2CH.CH2.C(OH)3,

2

yielding isovaleryl trihydrate, which is not completely decomposed on distillation and dissolves in thirty parts of water.

The metallic isovalerates have a fatty feeling, smell of valeric acid when damp, are mostly readily soluble in water, and in part crystallise therefrom with difficulty.

Baric isovalerate, Ba[O.CO.CH2.CH(CH3)2]2, H2O, forms thin prisms or plates, which dissolve in two parts of cold water, but in their own weight of water at 22°.

Zincic isovalerate, Zn(O.C,H,O)2, forms nacreous scales, which are more soluble in alcohol than in water. The salt is officinal.

Argentic isovalerate, AgO.C,H,O, crystallises in brilliant leafy plates, which require 450 parts of water for solution.

3. Eth-meth-acetic acid, CH(CH3)(C2H5).CO.OH, has been prepared synthetically by distilling ethylic eth-meth-aceto-acetate with sodic ethylate and saponification of the ethylic eth-meth-acetate so formed. The same acid appears to be formed by oxidation of optically active fermentation amylic alcohol (§ 170) with potassic dichromate and sulphuric acid. Obtained by this latter method, it rotates the plane of polarisation strongly to the right, whilst that prepared synthetically appears to be optically inactive. Otherwise the acids from both sources agree in properties. Eth-meth-acetic acid is a thin liquid of boiling point 173°. The argentic salt crystallises from hot water in feathery needles; the baric salt refuses to crystallise, leaving a gum-like mass on evaporation.

4. Trimeth-acetic acid, pseudo-valeric acid, or pinalic acid, (CH3)3 C.CO.OH, is obtained by heating trimethyl-carbin-cyanide with alkalies, or better with concentrated hydrochloric acid, to 100°, and by oxidation of pinacoline (§ 504, 3) with chromic and dilute sulphuric acids. The crude acid is converted into the potassic salt, this evaporated to dryness, and decomposed with sulphuric acid,

Trimeth-acetic acid then separates as an oil, which crystallises on cooling.

Trimeth-acetic acid forms leafy crystals, melting at 34°-35, and boils at 161°. It requires forty times its weight of water for solution. Its baric salt, Ba[O.CO.C:(CH3)3]2,5 H2O, and calcic salt:

Ca(O.C,H,O)2,4H2O,

crystallise in silky needles, which are readily soluble.

Caproic Acids, or Amyl Carbonic Acids, C¿H1902.

584. Of the eight possible isomeric amyl carbonic acids only the following have yet been prepared :—

1. Normal caproic acid, CH3.CH2CH2.CH2.CH.CO.OH, occurs in nature partly in the free state (in sweat and in the blood of Satyrium hircinum), partly in several fats as glyceric salts (in butter and cocoa-nut oil), and is formed from albuminoids and acids richer in carbon by oxidation. It is obtained from normal primary hexylic alcohol by chromic and sulphuric acids, and from normal primary amylic iodide by conversion into the cyanide and decomposition of this latter by alkalies. It is formed also in pretty considerable quantity in the butyric fermentation of sugar. In order to purify it the calcic or baric salt is prepared, recrystallised, and the caproic acid separated by addition of the hydrochloric acid.

Caproic acid is an oily liquid of faint, unpleasant odour, not miscible with water, having at 0° sp. gr. 945. On strong cooling it solidifies to a crystalline mass, which melts at -2°. It boils at 205°. Calcic caproate, Ca(O.CO.CH2.CH2.CH2.CH2.CH3)2, H2O, crystallises in plates, which dissolve in 36-37 parts of water at 19°. Baric caproate, Ba(O.C6H110)2, requires about twelve times its weight of water at 20° for solution.

Argentic caproate is nearly insoluble in water.

2. Isocaproic acid, CH3>CH.CH2.CH2.CO.OH, or isoamyl carbonic acid, is obtained from isoamylic cyanide by decomposition with alcoholic potassic hydrate and by saponification of ethylic aceto-isobutyl acetate. It is an oil resembling the normal acid, of sp. gr. -931, and boiling at 199°-200°.

Calcic isocaproate, Ca[O.CO.CH.CH2.CH: (CH3)2]23H,O, crystallises in plates, and requires nine parts of water at 18-5° for solution.

3. If the secondary isoamylic iodide be heated in alcoholic solution with potassic cyanide, the resulting cyanide decomposed by alkali, and the alkaline salt treated with acid, methyl-isopropyl acetic acid, CH CHCH.CH COOH' is obtained in the free state as an oil of fearful odour, which has been little investigated. Its calcic salt is difficultly soluble in hot water and crystallises in scales.

CH3

CH3.CH2

4. Dieth-acetic acid, CH3CH2CH.CO.OH, is obtained by saponification of its ethylic salt, which latter is a product of the splitting up of aceto-diethyl acetate. The free acid is an oil; the baric salt, Ba[O.CO.CH(CH3)2]2, is crystalline and readily soluble in

water. The argentic salt, AgO.CO.CH(CH3)2, is also soluble, and crystallises in asbestos-like, silky needles.

5. Dimeth-eth-acetic acid, C(CH3)2(C2H5).CO.OH, is obtained by heating dimethyl-ethyl carbin-cyanide with strong hydrochloric acid at 100°. It is a colourless liquid, insoluble in water, boiling at 187°.

Baric dimeth-eth-acetate, (C,H,CO.O),Ba,5H2O, crystallises in large transparent plates. The zincic salt forms transparent prisms, and the silver salt fine silky needles.

Heptylic Acids, or Hexyl Carbonic Acids, C,H1402.

585. Only two of the numerous possible hexyl carbonic acids have been accurately investigated.

Normal heptylic acid, or ananthylic acid:

CH3.CH2.CH2.CH2.CH2.CH2.CO.OH,

is obtained from normal primary hexylic iodide by conversion into normal primary hexylic cyanide by treatment with potassic cyanide and decomposition with alcoholic potassic hydrate, and also by the oxidation of normal primary heptylic alcohol. It is prepared most readily by the oxidation of its aldehyde, oenanthol (§ 400). It forms a colourless oil of faint odour and of sp. gr. 9345 at 0°, solidifying in the cold to a crystalline mass, melting at -10.5° and boiling at 223°-224°.

The calcic salt, Ca(O.C,H130)2, H2O, crystallises in tufts of needles, which dissolve in 106 parts of water at 8°.

Isonanthylic acid, probably (CH3)2: CH.CH2.CH2.CH2.CO.OH, is prepared by oxidation of isonanthylic alcohol. It is a colourless, oily liquid of peculiar and disagreeable odour; it boils at 210°-213°. Another isœnanthylic acid, boiling at 220°, is obtained by heating a mixture of sodic ethylate and isovalerate in carbonic oxide.

Acids Richer in Carbon.

586. In most cases only one representative of each higher member of the series is known, although the number of possible isomers increases enormously with each additional carbon atom. With few exceptions they are prepared from the fats, and those so obtained appear to be normal acids, CH3(CH2)nCO.OH, as on oxidation with chromic and sulphuric acids they yield normal acids poorer in carbon. They are insoluble in water, soluble in alcohol and ether, and are crystallisable. Their alkali salts are true soaps, i.e. dissolve in little water to a clear solution, but are partially decomposed by much water, with clouding and liberation of some alkali, to liquids which froth strongly on shaking. The other metallic salts are most difficultly soluble or insoluble in water, but mostly soluble in alcohol.

587. Octylic or caprylic acid, CH16O2 = CH15.CO.OH, the carbonic acid of normal primary heptyl, is prepared by oxidation of normal primary octylic alcohol (§ 173), and occurs in wine fusel oils, as a fat in butter, in cocoa-nut oil, and in other vegetable fats.

Caprylic acid crystallises in fine needles or plates, which melt between 16° and 17° and smell like sweat. It boils at 232°-234°.

Its baric salt requires fifty parts of cold, and more than 100 parts of hot, water for solution.

An iso-octylic acid, C(CH3)3.CH2.CH(CH3).CO.OH, is prepared by oxidation of diisobutylene; it is an oily liquid, boiling, apparently with some decomposition, at 205°-218°.

=

588. Nonylic acid, or pelargonic acid, CgH18O2 CH17.CO.OH, occurs in the essential oil of Pelargonium roseum, and is obtained by oxidation of methyl-nonyl ketone, the essential oil of Ruta graveolens (§ 455), with nitric acid, and also by acting on ethylic heptyl acetoacetate with solid potassic hydrate and acidulation of the resulting salt. It is solid below 12° and boils at 253°-254°.

Methyl-hexyl acetic acid, CH15.CH(CH3).CO.OH, is prepared from the cyanide derived from methyl-hexyl carbinol. It is a colourless oil, boiling at 245°.

589. Capric acid, C10H2002 = C,H19.CO.OH, occurs as glyceric salt in butter, in cocoa-nut oil, and all fats which contain caproic or caprylic acids. It is solid and crystalline, melts at 30°, boils at 270°, and has a faint, goat-like odour. The baric salt is scarcely soluble even in hot water.

590. Undecylic acid, CH22O2 = C10H21.CO.OH, obtained by the oxidation of methyl-undecyl ketone (§ 455a), melts at 28.5° and boils at 212°-213° under a pressure of 100 mm.

591. Lauric acid, C12H24O2 = C13H23CO.OH, obtained from the fat of pichurium beans, the fruit of Laurus nobilis, butter, cocoa-nut oil, &c., crystallises in spear-like, silky needles, which melt at 43.6° and have sp. gr. 883. It boils at 225.5° under a pressure of 100 mm., but is partially decomposed on distillation at ordinary pressures.

592. Tridecylic acid, C13H26O2 = C12H25.CO.OH, obtained by oxidation of methyl-tridecyl ketone (§ 4556), melts at 45° and solidifies a little below this to scaly crystals. It boils at 236° under a pressure of 100 mm.

C14H2802

593. Myristic acid, C11H2O2 = C13H27.CO.OH, forms a glyceric salt, the chief constituent of muscat butter (the fat of the fruit of Myristica moschata), but is also prepared from spermaceti, cocoa-nut oil, and other fats. It crystallises from alcohol in silky needles, which melt at 54°. Under a pressure of 100 mm. it boils at 248°.

594. Pentadecylic acid, C15H30O2 = C14H29.CO.OH, prepared by the oxidation of methyl-pentadecyl ketone (§ 455c), forms nacreous scales, which melt at 51° and boil at 257° under a pressure of 100 mm.

595. Palmitic acid, C16H32O2 = C15H31.CO.OH, occurs as a gly. ceric salt in nearly all animal and vegetable fats. In the solid animal fats it occurs mostly with stearic and oleic acids, in olive oil with little but the latter. It is obtained from its mixture with stearic acid (stearine candles' material) by the method of fractional precipitation (§ 563), and more readily from olive oil. This is saponified by boiling with sodic hydrate, when the thick solution contains glycerine and the soda soaps of oleic and palmitic acids. These ar precipitated on saturating the water with common salt, separated from the salt solution, dissolved in pure water, and precipitated by addition of plumbic acetate as plumbic oleate and palmitate (lead plaster). From this mixture the plumbic oleate is completely removed

by extraction with ether, and the residual plumbic palmitate decomposed by alcoholic hydrochloric acid. The alcoholic liquid, filtered from plumbic chloride, yields, when precipitated with water, nearly pure palmitic acid, which must be recrystallised several times from alcohol.

Palmitic acid is also obtained by heating cetylic alcohol with solid alkalies:

C15H31.CH2.OH + HOK = 2H2 + C15H31.CO.OK,

and from oleic acid by heating with potassic hydrate.

Palmitic acid crystallises in needles, which melt at 62° and resolidify in leafy crystals on cooling; it boils at 268.5° under a pressure of 100 mm.

The alkaline salts are soluble in alcohol and little water, and are true soaps; all other metals yield insoluble soaps with palmitic acid.

An isomeric acid, diheptyl acetic acid, CH(C-H15)2.CO.OH, is prepared by action of ethylic diheptyl aceto-acetate on solid potassic hydrate. It forms a paraffin-like mass, melting at 26°-27° and boiling at 240°-250° under 80-90 mm. pressure.

596. Margaric acid, cetyl carbonic acid :

C17H34O2 = C15H31.CH2.CO.OH,

is obtained from cetylic cyanide by boiling with potassic hydrate solution, and also by oxidation of methyl-heptadecyl ketone (§ 455c). It resembles palmitic acid, melts at 59.9°, and boils at 277° under a pressure of 100 mm.

597. Stearic acid, C18H36O2, or C17H35.CO.OH, occurs especially in the solid animal fats, and, mixed with palmitic acid, forms the material used for making stearine candles. To prepare this latter, solid animal fats are heated with water, to which a very small quantity of sulphuric acid has been added, for some time to 200°. According to the equation:

C3H5(O.CnH2n-10)3 + 3H20= C3H¿(OH)3 + 3HO.CnH2n_10, the fats are decomposed into glycerine, which remains dissolved in the excess of water, and a mixture of stearic, palmitic, and oleic acids, which float on the surface of the liquid. This is removed after solidification, and strongly compressed by hydraulic presses, first at ordinary temperature, later at 30°-40°, in order to remove the liquid oleic acid. The mixture of solid acids melts at a lower temperature than palmitic acid, and, after addition of some wax or paraffin to hinder crystallisation, is employed for stearine candles.

Pure stearic acid, which can be prepared from this mixture by the method of fractional precipitation, melts at 69.2°, solidifies in scaly crystals, and is obtained from alcoholic solutions in brilliant plates.

At ordinary pressure stearic acid only distils with decomposition : at a pressure of 100 mm. it distils unaltered at 287°, and also passes over at 250°-350° in a current of super-heated steam.

A fused and resolidified mixture of equal molecules of stearic and palmitic acid, which contains the elements in the same proportion as margaric acid :

C18H3602 +C16H32O2 = C34H68O4 = 2C17H34027