284 MYRTACE^. 



but has its internal tissue far more porous than the walls. The whole 

 calyx is of a deep rich brown, has a dull wrinkled surface, a dense 

 fleshy texture, and abounds in essential oil which exudes on simple 

 pressure with the nail. Cloves have an agreeable spicy odour, and a 

 strong biting aromatic taste. 



The varieties of cloves occurring in commerce do not exhibit any 

 structural differences. Inferior kinds are distinguished by being less 

 plump, less bright in tint, and less rich in essential oil. In London 

 price-currents, cloves are enumerated in the order of value thus : 

 Penang, Bencoolen, Amboyna, Zanzibar. 



Microscopic Structure — A transverse section of the lower part of 

 a clove shows a dark rhomboid zone, the tissue on either side of which 

 is of a lighter hue. The outer layer beneath the epidermis exhibits a 

 large number of oil-cells, frequently as much as 300 mkm. in diameter. 

 About 200 oil-cells may be counted in one transverse section, so that 

 the large amount of essential oil in the drug is well shown by its 

 microscopic characters. The above-mentioned zone is chiefly made up 

 of about 30 fibro-vascular bundles, another stronger bundle traversincf 

 the centre of the clove. The fibro-vascular bundles, as well as the tissue 

 bordering the oil-cells, assume a greenish black hue by alcoholic per- 

 chloride of iron. Oil-cells are also largely distributed in the leaves, 

 petals and even the stamens of Eugenia. 



Chemical Composition — Few plants possess any organ so rich in 

 essential oil as the drug under consideration. The oil known in phar- 

 macy as Oleum Caryo2)hylli, which is the important constituent of 

 cloves, is obtainable to the extent of 16 to 20 per cent. But to extract 

 the whole, the distillation must be long continued, the water being 

 returned to the same material. 



The oil is a colourless or yellowish liquid with a powerful odour 

 and taste of cloves, sp. gr. 1'046 to 1'058. It is a mixture of a hydro- 

 carbon, and an oxygenated oil called Eugenol, in variable proportions. 

 The former which is termed light oil of cloves and comes over in the 

 first period of the distillation, has the composition C^^H^^, a sp. gr. of 

 0-918 and boils at 251° C. It deviates the plane of polarization slightly 

 to the left, and is not coloured on addition of ferric chloride ; it is of a 

 rather terebinthinaceous odour. 



Eugenol, sometimes called Eugenic Acid, has a sp. gr. of 1*087 at 

 0° C, and possesses the full taste and smell of cloves. Its boiling 

 point is 247 °'5. With alkalis, especially ammonia and baryta, it yields 

 crystallizable salts. Eugenol may therefore be prepared by submitting 

 the crude oil of cloves to distillation with caustic soda ; the " light 

 oil" distils then, the eugenol, being now combined with sodium, 

 remains in the still. It will be obtained on addition of an acid and again 

 distilling. Eugenol is devoid of rotatory power, whence the crude oil 

 of cloves, of which eugenol is by far the prevailing constituent, is 

 optically almost inactive. The constitution of eugenol is given by the 



rocff 



formula C^H* \ OH . It belongs to the phenol class, and has 



(CH.CH.Cff 

 also been met with in the fruits of Pimenta oflicinalis (see next 

 article), in the Bay leaves, in Canella bark (see page 75), in the 



