Resorcin.

Meta-di-hydroxy-benzene.

C6H4.(OH)2(1:3)

Hydroquinone

Hydroquinone.

Para-di-hydroxy-benzene.

C6H4.(OH)2(l : 4)

When three atoms of hydrogen in benzene are replaced by hy-droxyl we get tri-hydroxy-benzene - pyrogallol or pyrogallic acid.

Tri hydroxy benzene. Pyrogallol

Tri-hydroxy-benzene. Pyrogallol.

When two atoms of hydrogen in benzene are replaced, the one by hydroxyl (OH) and the other by carboxyl (CO.OH), we get three isomers, salicylic acid, oxybenzoic acid, and para-oxybenzoic acid.

alicylic Acid

Salicylic Acid.

Oxybenzoic Acid

Oxybenzoic Acid.

Para oxybenzoic Acid

Para-oxybenzoic Acid.

Pyridine (C5H5N) is probably formed by one atom of tetrad C in the benzene ring being replaced by triad N :

Naphthaline (C10H8)

Naphthaline (C10H8) is formed by the union of two benzene groups, thus:

Chinoline (C9H7N)

Chinoline (C9H7N) is formed by the union of benzene and pyridine groups:

Chinoline

Chinoline is closely connected with quinine, from which it may be produced, and it is probable that many of the organic alkaloids are closely related to the aromatic series.

That morphine, for example, is related to phenol is shown by the fact that when morphine is treated with nitric acid and heated with water under pressure, it yields tri-nitrophenol, or picric acid.1

General Action. - The distinctive action of the lower members of the fatty series is their stimulant and anaesthetic action on the nerve-centres (p. 760). The most marked action of the lower members of the aromatic series is their antiseptic and antipyretic power. The antiseptic action appears to be very easily modified by slight changes in some substances of this group. Thus salicylic acid is antiseptic, but its sodium salt is not; and meta- and para-oxybenzoic acids, which are isomeric with salicylic acid, have no antiseptic power. The members of the aromatic series also affect the nervous system, but they appear to affect the motor centres more than the sensory, so that instead of producing anaesthesia, like the members of the fatty series, they tend rather to produce tremor, convulsions, and paralysis. Benzene, chlorobenzene, bromobenzene, and iodo-benzene are all somewhat similar in their action upon frogs; the halogen radicals not modifying the action of the benzene to such an extent as they do in the case of ammonium salts. The voluntary muscles are weakened by them and there is a slight tendency to paralysis of the motor nerves; but the action is chiefly exerted on the brain and spinal cord. The brain is first affected, as shown by general lethargy and disinclination to move. Next the cord is affected; motions are imperfectly performed, and there is a tendency to general tremor on movement resembling that observed in disseminated sclerosis; sometimes, however, the tremor is observed independently of movement (Brunton and Cash).

The addition of hydroxyl into the benzene nucleus intensifies the convulsant action, so that oxybenzene (carbolic acid) and dioxybenzene cause convulsions in frogs, and trioxybenzene causes jerkings, though of a slighter character.

1 Chastaing, Compt. Rend., xciv. 44.

All the members of the pyridine and chinoline series destroy life, either by exhaustive convulsions or by gradual paralysis of the respiratory centres.1 The members of the pyridine series-pyridine, picoline, lutidine, etc. - have an action similar in kind, but differing in degree, the lethal power increasing as one ascends in the series. The higher members of the pyridine series have an action like that of the lower members of the chinoline series, but are more liable to cause death by asphyxia than the chino-lines, and have more than twice their lethal power.

In ascending the chinoline series, a change occurs in the physiological action of its members, the lower ones acting chiefly on the sensory centres of the brain and reflex centres of the cord, destroying voluntary and reflex movement; while the higher act chiefly on the motor centres, first as irritants causing violent convulsions, and afterwards producing paralysis.

'On comparing the action of such compounds as chinoline (C9H7N) with parvoline, etc. (C9H13N), or collidine (C8H11N) with coniine (C8H15N), or dipyridine (C10H10N2) with nicotine (C10H14N2), it is observed that the physiological activity of the substance is, apart from chemical structure, greatest in those bases containing the larger amount of hydrogen. Further, when the bases of the pyridine series are doubled by condensation, as in dipyridine, parapicoline, etc., they become not only more active physiologically, but have a different action from that of the simple bases.'2

As alterations in the physiological action of the carbon compounds of this group can be effected by slightly changing their chemical composition, several attempts have been recently made to obtain artificial alkaloids which should possess a strong antipyretic action without depressing the heart or causing sickness. Antipyrin, one of the most recent introductions, appears to be the best as yet, but further attempts in this direction may be still more successful.

U.S.P. Acidum Carbolicum Crudum. Crude Carbolic Acid.

Characters. - A nearly colourless or reddish-brown liquid of a strongly empyreumatic and disagreeable odour, having a benumbing, blanching, and caustic effect on the skin or mucous membrane, and a neutral reaction.

Reactions and Tests. - Bromine water produces in an aqueous solution of carbolic or cresylic acid a white flocculent precipitate. Crude carbolic acid should not dissolve in less than 15 parts of water at 15° C. (59° F.), nor should the solution have an alkaline reaction (absence of alkalis). If 50 volumes of crude carbolic acid be diluted with warm water to measure 1,000 volumes, the mixture well shaken, cooled, and allowed to separate, the amount of undissolved impurities should not exceed 5 volumes or 10 per cent. by volume of the crude acid.

1 McKendrick and Dewar, 'On the Physiological Action of the Chinoline and Pyridine Bases,'Proc. Boy. Soc, 1874, p. 432. 2 McKendrick and Dewar, op. cit.