tillation or by heating the alcoholic solution to 120°-130°; it is also obtained from oxytetraldine (§ 424):

Ethylidene dichloride is also converted into collidine by ammonia solution at 160°. It is a colourless liquid, little soluble in water, of sp. gr. 944 and boiling point 179°.

The following higher homologues have been separated from coal tar, but have been little investigated: parvoline (C,H13N3, boils at 188°), corindine (C10H15N, boils at 211°), rubidine (C11H,N, boils at 230°), and viridine (C12H19N, boils at 251°).

DERIVATIVES OF THE HYDROCARBON NUCLEUS, CnH2n - 6

MONOBASIC ACIDS.

893. Mannitic acid, C,H(OH)5.CO.OH, results, along with its aldehyde, mannitose (§ 873), when a concentrated aqueous solution of mannite is oxidised by platinum black. It is an amorphous, extremely soluble substance. It forms salts which contain mostly two equivalents of a metal, one equivalent probably replacing a hydroxylic hydrogen atom.

Gluconic acid, isomeric with the above, is obtained from grape sugar, or glucose, by oxidation with chlorine. The acid is a colourless syrup, and forms monobasic salts, mostly soluble with the exception of the calcium one. The acid is optically active.

894. Lactonic acid, CH(OH)3.CO.OH, obtained by oxidation of arabin and milk sugar, is a deliquescent crystalline mass, melting at 100°. It seems to stand in the same relation to the previous acids that mannitan does to mannite and glucosan to grape sugar. It takes up two equivalents of metal from basic hydrates, but only one from carbonates.

DIBASIC UNSATURATED ACIDS, CH2n-4.04, or CnH2n' - 2(CO.OH)2.

895. In this group is included with certainty only acids of the formulæ CH,O, (fumaric and maleïc acids), CH604 (pyrocitric acids), and CHO, (hydromucic acids), to which the camphoric acids, C10H1604, may probably be added; but, as their constitution is less accurately known, they will be described later on under the oxidation products of the camphors.

As unsaturated compounds in whose hydrocarbon radical, CnH2n - 29 a double connection of neighbouring carbon atoms takes place, they possess the power of combining directly with two atoms of a halogen, with the elements of a molecule of hydric haloid, or with two atoms of hydrogen. In the latter case acids of the series CnH2n(CO.OH)2 result, or, by addition of halogens and their hydrides, mono- or di-substitution products or derivatives of the same.

Acids, CHO, or CH(CO.OH)2.

896. 1. Fumaric Acid. This acid exists on many plants-e.g. fumitory (Fumaria officinalis), Iceland moss, and several fungi.

Artificially it may be conveniently obtained by heating malic acid for some time to 150°, until water ceases to distil over:

Malic acid may also be converted into fumaric by boiling with fuming HCl. Monobrom-succinic acid splits up at 160° into fumaric acid and hydric bromide.

Fumaric acid crystallises in small prisms, which cannot be fused without undergoing change. In cold water they are very difficultly soluble. Of its salts only those of the alkalies are easily soluble. The barium and calcium salts, C,H,BaO, and C,H,CaO,, are difficultly soluble crystalline precipitates; the silver salt a perfectly insoluble amorphous powder, which explodes on heating. The alkaline salts yield acetylene on electrolysis:

Ethylic fumarate, C2H2(CO.O.C2H5)2, is obtained on distillation of ethylic malate and by saturating a solution of a mixture of fumaric acid and ethyl alcohol with hydric chloride, or still better by the action of ethylic iodide on argentic fumarate. It is a colourless oily liquid, boiling at 218°, which on contact with ammonia quickly passes into insoluble fumaramide:

C,H,(CO.NH,),

Fumaric acid distilled with phosphoric pentachloride gives chlor fumaryl:

C2H2(CO.OH)2 + 2PC15 = 2POCI ̧ + 2HCl + C2H2(CO.Cl)2,

a liquid boiling at 160°, reproducing on contact with water fumaric acid and hydric chloride.

Fumaric acid combines directly with nascent hydrogen to form ordinary succinic acid, and with a molecule of bromine yielding dibrom-succinic acid.

2. Maleic Acid. This acid is formed in considerable quantity by the quick distillation of malic acid, and can also be produced from fumaric acid.

If the latter acid be distilled it splits up into water and an anhydride, C2H2(CO),O, which on again combining with water forms

maleïc acid.

Maleïc acid is easily soluble in cold water and crystallises in colourless leafy crystals, melting at 130°; at 160° it breaks up into water and the anhydride. The acid, if fused and maintained for some time at about its fusing point, solidifies on cooling to fumaric acid; this change can also be effected by boiling with dilute sulphuric, hydrobromic, or hydriodic acids. Nascent hydrogen converts it into ordinary succinic acid, bromine into isodibrom-succinic acid. salts, including those with barium and calcium, are somewhat easily soluble in water. The neutral silver salt, C2H2(CO.OAg)2, is at first amorphous, but crystallises after some time. An acid salt,

Its

C2H2(CO.OH.) (CO.OAg), forms colourless needles when a solution of the acid and argentic nitrate are mixed and allowed to stand for some days. By electrolysis salts of maleïc acid, like those of fumaric, yield acetylene.

=== 3

Maleic anhydride, CH2O, CH3COO, obtained from fumaric or maleïc acid by repeated distillation, is a colourless crystalline mass, melting at 57° and boiling at 196°.

Acids, CsH6O, or C3H,(CO.OH)2.

897. Three acids (itaconic, citraconic, mesaconic) of this formula are known isomeric with paraconic acid (§ 866). They are collectively obtainable from citric acid and may be termed generally pyrocitric acids. They are related to each other in constitution, somewhat similarly to fumaric to maleïc acids, giving, on distillation along with water, the same anhydride, C3H4(CO)2O, which on again taking up the elements of a molecule of water gives citraconic acid; hence this anhydride is termed citraconic anhydride. All three acids combine with two atoms of nascent hydrogen and pass into pyrotartaric acid. As the structure of the latter (§ 838, 2) acid is known, only two formulæ are possible for the three pyrocitric acids :

so that one of them must represent at least two acids.

Recent experiments have shown that salts of itaconic acid on electrolysis yield isallylene. The formulæ of itaconic acid must be therefore :

Citraconic and mesaconic acids, however, give allylene, and therefore both are represented by the first of the above formula:

CH..C.CO.OK

CH3.C

CH.CO.OR

+ OH2 =

+ K2CO3 + H2 + CO2 CH

The first step in their preparation consists in the dry distillation of citric acid, whereby water is split off and aconic acid results :

C3H,(OH)(CO.OH)3 = OH, + C3H3(CO.OH)3,

which decomposes further into CO2 and itaconic acid :

C3H3(CO.OH)3 = CO2 + C3H1(CO.OH)2,

the latter acid being at the same time partially further decomposed into water and citraconic anhydride. The well-cooled distillate divides itself into an upper oily and a lower aqueous layer, from both of which, on cooling, itaconic acid crystallises out. The portion of the oily layer remaining liquid is mostly citraconic anhydride, whilst the watery portion is a solution of the easily soluble citraconic acid.

1. Itaconic acid may be also formed by heating citric acid with water to 160°. It crystallises in rhombic prisms, soluble at 10° in

17 parts of water and melting at 161°. It combines with hydric haloids to itahaloid pyrotartaric acids (§ 866, 1).

Its salts are mostly pretty easily soluble, the lead and silver salts difficultly so. Ethylic itaconate, C3H (CO.O.C2H5)2, boils at 227°.

2. Citraconic acid forms large shining four-sided prisms, which dissolve in less than their equal weight of water and melt at 80°. At 100°, or more quickly by heating a concentrated solution to 120°, it is changed into itaconic acid. Hydric chloride forms with it the very unstable citrachlor-pyrotartaric acid.

3. Mesaconic acid is produced by long heating of citraconic acid with dilute nitric or strong hydric chloride or iodide. Mesaconic acid crystallises in fine shining needles, which dissolve in 37 parts of water at 18° and melt at 208°. It combines with hydric chloride to form mesachlor-pyrotartaric acid, and splits up by dry distillation into citraconic anhydride and water.

Citraconic anhydride, C3H, COO, is an oil boiling at 212°, which gives with PC1, chlor-citraconyl, CH,(CO.Cl)2, an oily body boiling at 175°.

898. 1. Hydromuconic acid, CH ̧O1 = C1H6(CO.OH)2, is derived from mucic acid by the action of sodium amalgam on the dichloride (see mucic acid):

C1H2Cl2(CO.OH)2 + 6Na + 20H2 = C1H(CO.ONa)2

+2NaCl + 2NaOH.

It forms long prisms, difficultly soluble in water and melting at 195°, which by further addition of hydrogen passes into adipic acid (§ 839) and takes up two atoms of bromine to form dibrom adipic acid.

allyl-malonate, is isomeric with the above acid and melts at 103°.

3. Xeronic acid, |

CH2.C(CH3).CO.OH

CH,.C(CH,)CO.OH

is contained in the distil

late from citraconic anhydride, and may be separated by distilling the mixture of anhydrides with steam, when xeronic anhydride passes over. It boils at 242° and is liquid at -18°. The acid does not appear to exist in a free state, but salts are known.

The acid is polymeric with methyl acrylic acid, to which it probably stands in the following relation :