ARONIA. 



ARRAGONITE. 



310 



that at which it could be distilled, it has been imagined that some 

 principle of a more subtile nature exists in which the odour resides, 

 and that it is this which imparts smell to the oil. In fact, however, 

 the property of odour belongs to proximate vegetable principles of 

 different kinds, in which there is no reason to suppose the existence 

 of any common' principle ; essential oil is unquestionably the most 

 usual cause of its production, and it is capable of being volatilised in 

 small quantity at a low temperature, and thus diffused through the 

 atmosphere or communicated to water. 



ARONIA, the Limuean name for a species of plants of the genus 

 ifetpilux, the Mtipilm A melanch ier, or Jfespilus vulgar ii. [AMELAN- 

 CHIER ; MESPILCS.] 



ARQUERITO, a native amalgam, consisting of six parts of silver 

 and one of quicksilver. It has been regarded as native silver. It ia 

 malleable, and is worked with great success in the mines of Arqueros 

 in Chile. 



ARRACA'CHA, a genus of plants belonging to the natural order 

 L'mbelliferfe, which comprehends a species of as much importance in 

 the tropical parts of America as the parsnip and carrot are in Europe. 

 This plant, the A rraeacha esculenta of botanists, is cultivated in great 

 quantities in the neighbourhood of Santa 6 de Bogota, in the cooler 

 districts among the mountains, and in other parts of the state of 

 Colombia, where it is called Arracacha. It resembles the common 

 hemlock in appearance, but the leaves are much broader, the stems 

 are not spotted, and the flowers are of a dingy purple colour ; it is 

 also of smaller stature. 



The root is of the same nature as the tuber of a potato, only it is 

 forked, or divided into several lobes, each of which is about the size 

 of a large carrot These when fit for eating are boiled like the 

 potato, and become of a firm but tender consistence, not at all mealy, 

 and have a flavour intermediate between a chestnut and a parsnip. It 

 appears that an immense produce of Arracacha is obtained in the 

 South American provinces, where it has long been as much the staple 

 nutriment of the population as the potato or the yam ill other places ; 



The Arracacha (Arracacha etculentn' 

 1, A barren flower ; 2, a fertile flower ; 3, a stamen ; 4, a petal ; 

 5, a ripe fruit ; 6, the same cut across. 



and as it will only thrive in the colder districts, it was once expected 

 to form an important agricultural plant in Europe. It has however 

 been found upon trial unable to accommodate itself to our uncertain 

 climate, and to perish as soon as the cold nights and damp weather 

 of autumn approach, without having been able during the summer to 



perfect its tubers. It is therefore only cultivated now in botanical 

 collections. (Hooker, Botanical Magazine, tab. 3092.) 



ARRAGONITE, Prismatic Carbonate of Lime, called by Mohs the 

 Prismatic Lime-Haloide. It is a mineral substance consisting of 

 carbonic acid and lime, admitting of cleavage in planes parallel to the 

 faces of a right rhombic prism of 116 5' and 63 55', which may 

 therefore be considered as its fundamental form (fg. 1). The most 

 general modifications which occur consist either in the removal of the 

 four acute angles at A by planes a intersecting each other in the 

 short diagonal B B, and inclined to each other at an angle of 108 18', 

 by which the face P being entirely removed, the form of fg. 2 is pro- 

 duced ; or the change may be eifected by the truncation of the acute 

 lateral edges of the prism by planes parallel to the axis of the crystal, 

 and therefore inclined to the faces L, at 121 57', giving rise to the 

 form seen in fig. 3. These modified forms usually present themselves 

 in twin crystals, in which the short diagonals of the prism B B are 

 placed at right angles to one another, when only two crystals are 

 present, thus producing a very simple cross. It is usual however that 

 three of the crystals of fig. 3 cross each other, producing a crystal of 

 the appearance of fig. 4, which at first sight may be mistaken for an 

 hexagonal prism, but on a closer inspection it will be found that what 

 appeared to be a single face is really composed of two planes, making 

 a re-entrant angle. 



The intersections of the individual crystals with each other are 

 visible both in the lateral and terminal faces, and are indicated in 

 fig. 4 by the dotted lines. These crystals have been found abundantly 

 in a ferruginous clay in Aragon in Spain, where they occur accom- 

 panied by a sulphate of lime. From this circumstance the mineral 

 has derived its name. It has also been found very beautifully crystal- 

 lised in a vein of a massive variety of the same mineral traversing 

 basalt at Bilin in Bohemia. (Mohs.) Fine specimens have been found 

 at the following places in England : in the Dufton lead-mines ; in a 

 cavern of Grauwacke, near Merridge, Somersetshire ; and also in 

 several parts of Devonshire, &c. In an old coal-mine six miles south- 

 B B 



west of Cockfield, Durham, it is remarkable as occurring depending 

 from a roof of clay-slate, and accompanied by tubular calcareous 

 stalactites. (Phillips.) Varieties of this mineral are also common in 

 beds of iron-ore in the mines of Eisenerz in Styria, and in several 

 other iron-mines of Hungary, of Transylvania, &c., consisting of 

 numerous fibrous crystals, of a satin-like lustre, radiating from a 

 centre, and to these the name of Flos Ferri has been applied. 



In a chemical and crystallographical point of view Arragonite is 

 peculiarly interesting, as presenting to us carbonate of lime differing 

 in its system of crystallisation from that of the common Gale-Spar, 

 and thus affording us an instance of the influence of any difference in 

 the aggregation of matter in changing its physical properties, as will 

 be seen by comparing this substance with the rhombohedral Calc-Spar, 

 with which it agrees in chemical constitution. In the scale of Mohs 

 its hardness varies from 3'5 to 4, while that of Calc-Spar is 3. The 

 specific gravity of 



Arragonite is 2-931 



Calc-Spar . 2721 



They act also differently on light, the index of ordinary refraction of 



Arragonite being 1-693 



Calc-Spar .1-519 



Attempts have been made to account for these differences by con- 

 sidering them the effects of small quantities of carbonate of strontia, 

 which Professor Stromeyer first discovered to be contained in many 

 specimens of Arragonite ; but the conclusion is unfounded, as will be 

 seen by the results of two analyses given by Stromeyer : 



First. Second. 



Carbonate of Lime . . . 95'2965 . . 99-2922 

 Carbonate of Strontia . . 0-5090 . . 4-1043 

 Water 0'1544 . . 0'5992 



