CLAY 807 



CITRON*. (Citradier, Fr. ; Cedrato, Ital.) The fruit df the Citrus medico, be- 

 longing to the family of dicotyledonous plants, the Aurantiaccce or Hesperide. The 

 rind of this fruit candied is well known as a delicate sweetmeat. The tree producing 

 the citron is the most beautiful of the genus. A curious variety of the citron is 

 cultivated in China, and called the fingered citron, from its lobes all separating into 

 fingers in different shapes and sizes. The fruits of several other genera belonging 

 to the family are greatly esteemed in the countries which produce them. See HES- 



CITKOWEiliE OIIi, An oil from the Lemon-grass (Andropogon citratiim). 



CITRUS. A genus of the family Aurantiacea, producing the orange, the lemon, 

 &c. 



CITRUS AURANTIUM. The common or sweet orange. 



CITBTJS BERGAMIA. The Bergamot orange. 



CITRUS BIGARADEA. The bitter or Seville orange, or bigarade. 



CITRUS DECUMANA. The shaddock. See SHADDOCK. 



CITRUS LISIETTA. The lime. See LIME. 



CITRUS LIMONIUM. The lemon. See LEMON. 



CITRUS MEDICA. The citron. 



CIVET. (Civettc, Fr. ; Zibeth, Ger.') The odour of this substance is peculiar 

 and very characteristic, and is even more persistent than musk. It forms the base of 

 the famous ' Jockey Club ' perfume. It is the product of two small quadrupeds of 

 the genus Viverra ( V, zibetha and V. civetta), of which the one inhabits Africa, and the 

 other Asia. They are reared with tenderness, especially in Abyssinia. The civet 

 is contained in a sac situated between the anus and the parts .of generation in 

 either sex. The animal frees itself from an excess of this secretion by a contractile 

 movement which it exercises upon the sac, when the civet issues in a vermicular 

 form, and is carefully collected. The negroes are accustomed to increase the 

 secretion by irritating the animal ; and likewise introduce a little butter, or rather 

 grease, by the natural slit in the bag, which mixes with the odoriferous substance, and 

 increases its weight. It is employed only in perfumery. 



According to M. Boutron-Chalard, it contains a volatile oil, to which it owes its 

 smell, some free ammonia, resin, fat, and extractiform matter, and mucus. It affords, 

 by calcination, an ash, in which there are some carbonate and sulphate of potash, 

 phosphate of lime and oxide of iron. 



CXiACK. The valve of a pump. See PUMP. 



CXiAUSTH AIiITE. A selenide of lead which occurs in the veins of haematite at 

 Clausthal and other mines in the Hartz, and at Kio Tinto in Spain. 



CX AY. (Arffile, Fr. ; Thon, Ger.). The term clay is applied to certain hydrous 

 silicates of alumina, derived for the most part, from the decomposition of felspathic 

 rocks, and which are generally rendered impure by the admixture of other substances. 

 Economically, the term is applied to any finely -divided mineral matter, which becomes 

 plastic on being wetted, and retains its shape when moulded or pressed into any par- 

 ticular form. Lime, magnesia, oxide of iron, with some other colouring metallic 

 oxides, are occasionally present in small quantities in certain natural clays : when 

 iron is present, the clay burns red. 



1. They are readily diffusible through water, and are capable of forming with it a 

 plastic ductile mass, which may be kneaded by hand into any shape. This plasticity 

 exists, however, in very different degrees in the different clays. 



2. They concrete into a hard mass upon being dried, and assume, upon exposure to 

 the heat of ignition, a degree of hardness sometimes so great as to give sparks by col- 

 lision with hardened steel. In this state they are no longer plastic with water, even 

 when pulverised. Tolerably pure cbys, though infusible in the furnace, become 

 readily so by the admixture of lime, iron, manganese, &c. 



3. All clays, even when previously freed from moisture, shrink in the fire by virtue 

 of the reciprocal affinity of their particles ; they are very absorbent of water in their 

 dry state, and adhere strongly to the tongue. 



4. Ochrey, impure clays, emit a disagreeable earthy smell when breathed upon ; the 

 odour is indeed observable to a greater or less extent in all clays. 



Brongniart. distributes Clays into : 



(1.) Fire-clays (argiles apyres, Fr ; Feuerfeste, Ger.). 

 (2.) Fusible (schmelsbare, Ger.). 



(3.) Effervescing (brausende, Ger.), from the presence of chalk. 

 (4.) Ochrey (ocreuses, Fr. ; ochrige, Ger.). 



The following are the chief varieties .of clay usually recognized : 

 I. SLATK-CLAY. (Schiefer-tkon, Ger). Its colour is grey or greyish-yellow; 

 massive, dull, or glimmering from admixture of pirticles of mica. Fracture slaty, 

 appi-oaching sometimes to eartiy. Fragments tabular ; soft, sectilo, and easily 



